Research activity information

• Discrepancies between feeding ecology and trophic position based on nitrogen isotopic composition in endosymbiont-bearing benthic foraminifers
  Ayumi Maeda; Yuichi I. Naito; Masashi Tsuchiya; Yoshito Chikaraishi; Kazuhiko Fujita; Naohiko Ohkouchi; Hodaka Kawahata
  Progress in Earth and Planetary Science, 13, 1, Springer Science and Business Media LLC, 11 Mar. 2026
  Scientific journal, Abstract
  
  Symbiotic relationships of microorganisms including eukaryotic algae and prokaryotes affect holobiont nitrogen metabolism and provide survival advantages in extreme environments; however, the influences of different symbionts on nitrogen metabolism in host organisms remain unclear. By tracing the nitrogen isotopic composition (δ ¹⁵ N) of amino acids (AAs), it is possible to constrain the biosynthetic sources and trophic interactions. We targeted reef-dwelling large benthic foraminifers hosting species-specific symbiotic algae to identify the trophic positions of multiple species with distinct feeding strategies. We measured δ ¹⁵ N in AAs of bulk organic matter and of foraminiferal shells and compared the feeding strategy of each species with its estimated trophic position (TP). Estimated TPs based on δ ¹⁵ N in AAs were inconsistent with respect to species-specific feeding strategies. In particular, Amphisorus kudakajimensis , which depends on heterotrophic feeding, showed light δ ¹⁵ N _Glu and δ ¹⁵ N _Phe and TP of ~ 1. A shared nutrient source for both host and symbionts and an interactive supply of trophic compounds may explain the low trophic position. The mixotrophic or heterotrophic TPs of Calcarinidae hosting endosymbiotic diatom with limited feeding (TP = 1.5–2.3) may be affected by bacterial heterotrophic processes. Differences in symbiotic algae (zooxanthellae and diatoms) may have influenced host’s nutritional strategies through functional variations in nitrogen metabolism. Large variations in δ ¹⁵ N _Glu and δ ¹⁵ N _Phe within single species suggested that large benthic foraminifers exploit multiple sources of nitrogen. Additional culture studies using different nitrogen sources could provide insights into detailed nitrogen metabolism of organisms with endosymbionts and role of associated organisms.
• Nitrogen and carbon flows in a microbial mat involving anaerobic oxidation of methane in northwestern Black Sea: perspectives from nitrogen and carbon isotopic composition of coenzyme F430 and its biosynthetic pathway
  Masanori Kaneko; Yoshinori Takano; Yuta Isaji; Nanako O. Ogawa; Yoshito Chikaraishi; Naoto F. Ishikawa; Hiroyuki Imachi; Yoshihiro Takaki; Miyuki Ogawara; Fumie Kabashima; Martin Krüger; Naohiko Ohkouchi
  Progress in Earth and Planetary Science, 12, 1, Springer Science and Business Media LLC, 06 Dec. 2025
  Scientific journal, Abstract
  
  Coenzyme F430, a nickel-containing tetrapyrrole, serves as a cofactor for methyl-coenzyme M reductase (MCR), which catalyzes both the final step of methanogenesis and the initial step of anaerobic oxidation of methane (AOM). Due to its central role in these metabolic processes, coenzyme F430 can be used as a biomarker to investigate the distribution and activity of methanogens and anaerobic methane-oxidizing archaea (ANMEs) in various environments. In the northwestern Black Sea, chimney-like microbial mats dominated by a subcluster ANME-1 in the internal pink mat and ANME-2 in the outer black mat provide a sufficient quantity of coenzyme F430 for both stable carbon and nitrogen isotope analyses. In this study, we report the stable carbon and nitrogen isotopic compositions of coenzyme F430 and its derivatives from ANME-1 and ANME-2, as well as those of cell components, including bulk mat, amino acids, and membrane lipids. The carbon isotopic compositions of coenzyme F430 exhibit significant ¹³ C-depletion, reflecting the incorporation of methane-derived carbon. In contrast, coenzyme F430 from ANME-1 is enriched in ¹³ C and depleted in ¹⁵ N compared to that from ANME-2. These isotopic differences between ANME-1 and ANME-2 cannot be explained solely by biosynthetic isotope effects and likely reflect sequential methane and ammonium consumption within the microbial mat, which is influenced by surrounding seawater with low sulfate concentrations.
• Purification of hydroxyproline for small-scale radiocarbon dating verified using archaeological bone collagen
  Yu Itahashi; Yoshinori Takano; Yoshito Chikaraishi; Nanako O. Ogawa; Naoto F. Ishikawa; Naohiko Ohkouchi; Masako Yamane; Yusuke Yokoyama; Minoru Yoneda
  Progress in Earth and Planetary Science, 12, 1, Springer Science and Business Media LLC, 01 Dec. 2025
  Scientific journal, Abstract
  
  We developed a novel technique for the accurate radiocarbon dating of single amino acids from archaeological human and animal remains. Despite the extensive use of bulk collagen for radiocarbon dating of archaeological bones, obtaining accurate dates can be difficult in some cases due to unremovable C contamination in collagen. To obtain a reliable, uncontaminated age, we developed a purification method for analysing hydroxyproline, a major amino acid in bone collagen. This method uses two purification processes: liquid–liquid extraction and recrystallization after high-performance liquid chromatography. This purification method substantially reduced the contamination by exogenous C in the isolated amino acids. The reliability of the method was demonstrated by radiocarbon dating an archaeological bone with a known date of death. This method enables compound-specific radiocarbon dating of amino acids with < 100 μg of C, reducing collagen and bone sample consumption relative to previous approaches. This method is expected to enable the extensive application of radiocarbon dating to degraded archaeological bones that were previously unusable. In addition, our technique of isolation and purification of amino acids is useful for the isolation of compounds for the radiocarbon analysis from diverse organic tissue beyond collagen and other organic molecules in marine sediments targeted by studies in the field of Earth and planetary science.
• Fatty acids as the main energy source in polyps of the jellyfish (Cnidaria: Aurelia aurita) for survival strategy under overpopulation: insights from compound-specific isotope analysis
  Nayeon Park; Hyuntae Choi; Yuko Takizawa; Yoshito Chikaraishi
  Progress in Earth and Planetary Science, 12, 1, Springer Science and Business Media LLC, 16 Oct. 2025
  Scientific journal, Abstract
  
  Jellyfish exhibit an extraordinary survival strategy in high-density populations that exceed the carrying capacity of ecosystems. It is particularly questionable how jellyfish can thrive in habitats where the concentration of toxic nitrogenous waste (i.e., NH₃) in the ambient water could be extremely high caused by high-density populations. However, physiological mechanisms of the survival strategy in jellyfish remain poorly understood, especially at the polyp stage, even though this stage is a key role in jellyfish population dynamics. In the present study, we investigated the trophic isotopic discrimination of amino acids and fatty acids in polyps of the jellyfish Aurelia aurita in controlled feeding experiments, to understand the metabolic flux of these organic substrates in the jellyfish physiology under high-density populations. Contrary to the general trophic isotopic discrimination observed in non-gelatinous organisms, the discrimination in the A. aurita polyps is close to zero for most amino acids (except for glycine and leucine), indicating a little activity of both biosynthesis and degradation of the amino acids. In contrast, the discrimination in the A. aurita polyps is considerably large for fatty acids (ranging from 18.4‰ (for C_18:0) to 50.5‰ (for C_18:2, n-6), indicating a large activity of degradation of fats (and its components, fatty acids). Based on these results, we conclude that A. aurita polyps prioritize the use of fatty acids compared to that of amino acids to produce life energy, for minimizing the production of nitrogenous waste derived from the amino acid degradation (about 0.0 mg/L for NH₃) and maintaining the quality of ambient water, and therefore for allowing them to survive in high-density populations. Moreover, these findings suggest the presence of metabolic plasticity among marine organisms. This plasticity may reflect flexible survival strategies supported by different metabolic pathways. Therefore, integrating the trophic isotopic discrimination of both amino acids and fatty acids can be useful for understanding these physiological mechanisms, as well as for accurately illustrating energy transfer along food chains in ecosystems.
  
  Graphical Abstract
• Nitrogen isotopic composition of amino acids reveals a variety of trophic ecology of organisms inhabiting chemosynthesis-based ecosystems
  Masashi Tsuchiya; Takao Yoshida; Yoshito Chikaraishi; Nanako O. Ogawa; Hidetaka Nomaki; Yoshihiro Fujiwara; Yasuhiko T. Yamaguchi; Yohei Tada; Robert G. Jenkins; Yoko Sasaki; Katsunori Fujikura; Naohiko Ohkouchi
  Progress in Earth and Planetary Science, 12, 1, Springer Science and Business Media LLC, 15 Oct. 2025
  Scientific journal, Abstract
  
  To understand the trophic interactions between various organisms in chemosynthesis-based ecosystems (CBEs) and the metabolic interaction between host animal and its symbiont, we estimated the trophic position (TP) using the stable nitrogen isotopic compositions of glutamic acid and phenylalanine. We demonstrated that estimating TP based on the isotopic composition of amino acids is a valuable tool for understanding photosynthetic prey-predator interactions among marine organisms, and it can also be applied to chemosynthesis-based food webs involving host-symbiont interactions. In CBEs, the nitrogen isotope ratio of phenylalanine ranged from − 15‰ to + 13‰, suggesting a wide variety of nutritional sources for organisms. Our results revealed that organisms in CBEs can be categorized into two main groups: those that depend on chemosynthetic organic matter and those that depend on photosynthetic organic matter from the ocean surface. Furthermore, although not clearly distinguishable, there was an intermediate group that depends on both, such as demersal fishes. CBE-endemic organisms, particularly bivalves, were notably depleted in ¹⁵N. Interestingly, two nutritional types of chemosymbiotic bivalves were identified: vesicomyid clams showed an increase in the nitrogen isotope ratio of glutamic acid and a higher TP relative to symbiotic bacteria, while Bathymodiolus and Gigantidas mussels exhibited no change in the nitrogen isotope ratio of glutamic acid and maintained a TP of ~ 1 across all tissues, including gill samples mainly composed of symbiotic bacteria. Different forms of trophic dependence on chemosynthetic bacteria were observed even among closely related bivalve species, regardless of whether the symbiotic relationship is ecto- or endo-symbiosis. Consequently, among species preying on chemosymbiotic bivalves, the TP may reach 3 or more when preying on vesicomyid clams but remains around 2 when preying on Bathymodiolus and Gigatidas mussels. The organisms inhabiting the CBE of Sagami Bay display diverse patterns of resource use.
• Fractionation of nitrogen isotopes in the enzymatic deamination of alanine: an insight into the quantitative evaluation of anaerobic metabolism in ecosystems
  Yuko Takizawa; Hyuntae Choi; Mio Shibuya; Nayeon Park; Prarthana S. Dharampal; Shawn A. Steffan; Yoshito Chikaraishi
  Progress in Earth and Planetary Science, 12, 1, Springer Science and Business Media LLC, 30 Sep. 2025
  Scientific journal, Abstract
  
  Nitrogen isotope ratios of amino acids have been employed as a tool for illustrating the resource utilization of organisms and the trophic transfer between organisms in food webs. This tool is proposed based on the empirical observation that a universal trophic enrichment in ¹⁵N is found in glutamic acid from diet to consumer species. Since glutamic acid is deaminated and incorporated into the tricarboxylic acid cycle (aerobic metabolism), the isotope ratios of glutamic acid have been used for evaluating life energy production through aerobic metabolism. However, little is known about the change in the isotope ratio associated with ‘anaerobic’ metabolism such as fermentation in organisms. Therefore, we determined the isotopic fractionation factor (α) for the deamination of alanine, a representative amino acid related to anaerobic metabolism, and conducted laboratory-cultured experiments to see the change in the nitrogen isotope ratio through anaerobic metabolism. Moreover, we compared the trophic enrichment in ¹⁵N between alanine and glutamic acid in natural samples to visualize the contribution of anaerobic metabolism in food webs. In the in vitro enzymatic deamination of alanine, the isotope ratios of alanine are gradually increased, with the α of 0.9923. In the culture of the eukaryote Saccharomyces cerevisiae and the bacterium Lactococcus lactis with organic substrates under hypoxic conditions, the enrichment in ¹⁵N is negligibly small for glutamic acid (by ~ 0‰), but considerably large for alanine (by ~ 5‰) in the culture. These results demonstrate that the activity of anaerobic metabolism is recorded in the isotope ratios of alanine but not glutamic acid in organisms. Moreover, we visualize the contribution of anaerobic metabolism in natural samples: (1) hypoxia within pollen provision for the diet of bee larvae induces a large enrichment in ¹⁵N of alanine; and (2) this ‘anaerobic’ enrichment in ¹⁵N can be identified in the cross-plot of the isotope ratios for alanine and glutamic acid in marine and terrestrial species, dissolved organic nitrogen, and the bees that potentially record of hypoxia within their diets. Thus, we suggest that the comparison of the isotope ratios between alanine and glutamic acid can be useful for evaluating the experience of hypoxia and the activity of anaerobic metabolism in biological and environmental samples.
• A compound-specific method for measuring the stable carbon isotopic composition of amino acids: elimination of the effect of isotopic fractionation during derivatization
  Yoshito Chikaraishi; Hyuntae Choi; Nayeon Park; Yuko Takizawa
  Progress in Earth and Planetary Science, 12, 1, Springer Science and Business Media LLC, 30 Sep. 2025
  Scientific journal, Abstract
  
  Compound-specific isotope analysis (CSIA) of carbon and nitrogen within amino acids by gas chromatography/isotope ratio mass spectrometry (GC/IRMS) has been employed as a powerful tool for estimating the trophic tendency and resource utilization of organisms in food webs, as well as for illustrating the metabolic fate of amino acids and associated energy flux in diverse levels from within a single organism to entire ecosystems. However, the polar functional groups (i.e., carboxyl, amino, and hydroxyl groups) of amino acids should be neutralized by derivatization (i.e., esterification followed by acylation) before injection into a GC/IRMS instrument, which has caused several serious issues. For instance, the toxicity of acylation reagents (e.g., pivaloyl chloride) and the fluorinated derivatives (e.g., derived from trifluoroacetic anhydride) have complicated the use of isotope ratio analysis of amino acids in our studies. Moreover, large isotopic fractionation in ¹³C/¹²C associated with the acylation has considerably reduced the accuracy of the analysis of carbon isotope ratios. In the present study, we therefore developed a new derivatization method to minimize these issues, which can reduce the isotopic fractionation in ¹³C/¹²C by following two sequential reactions for the acylation: the first is acylation, which introduces isotopic fractionation, and the second is replacement of the pivaloyl group with that of pivalic anhydride. Further, the contribution of the ¹³C/¹²C ratios of derivative groups (i.e., isopropyl and pivaloyl groups) can be completely removed by a simultaneous mass balance calculation. Also, the new method is relatively safe, without the use of toxic reagents and the production of fluorinated derivatives. Thus, this derivatization method can be useful for CSIA of amino acids in diverse studies, which promises to provide unprecedented accuracy in understanding the complex physiological, ecological, and geochemical dynamics across aquatic and terrestrial ecosystems.
• Impact of acetate on CO₂fixation pathways in thermophilic and hydrogenotrophic bacteria
  Yoko Chiba; Tomomi Sumida; Masafumi Kameya; Yuto Fukuyama; Tomoyuki Wakashima; Shigeru Shimamura; Ryoma Kamikawa; Yoshito Chikaraishi; Takuro Nunoura
  Cold Spring Harbor Laboratory, 01 Apr. 2025
  Abstract
  
  The Wood-Ljungdahl (WL) pathway and reductive tricarboxylic acid (rTCA) cycle are the dominant chemolithotrophic CO₂fixation pathways in bacteria inhabiting aphotic geothermal and deep-sea hydrothermal ecosystems. However, the activity of these bacterial metabolic systems in ecosystems with available organic carbons remains unclear. Here, we examined the impact of extracellular acetate on the CO₂-fixation pathways of three thermophilic hydrogen-oxidizing and non-acetogenic bacteria using¹³C tracer-based metabolomics. Under chemolithoautotrophic conditions,Thermodesulfatator indicusandHydrogenobacter thermophilusfixed CO₂through the WL pathway and rTCA cycle, respectively, whereasThermovibrio ammonificans, which has been suggested to operate both of these pathways, exhibited significant CO₂fixation through only the rTCA cycle. Under chemolithomixotrophic conditions with acetate,H. thermophilusandT. ammonificansassimilated both CO₂and acetate via the rTCA cycle. In contrast, acetate suppressed CO₂fixation through the WL pathway inT. indicusand was used as the primary carbon source under chemolithomixotrophic conditions. These results suggest that the contribution of the WL pathway for CO₂fixation might be overestimated in ecosystems where acetate is available. Moreover, the present findings indicate that simultaneous CO₂fixation through both the WL pathway and rTCA cycle in a cell, which has been proposed as a possible metabolic strategy for CO₂-fixation in ancestral life, is not advantageous in extant microorganisms.
• Magnesium isotopic variation in marine fish organs
  Toshihiro Yoshimura; Naoto F. Ishikawa; Nanako O. Ogawa; Soichiro Kusaka; Shigeyuki Wakaki; Tsuyoshi Ishikawa; Kazuya Nagaishi; Masanori Kaneko; Yuta Isaji; Yoshito Chikaraishi; Naohiko Ohkouchi
  Progress in Earth and Planetary Science, 12, 1, Springer Science and Business Media LLC, 06 Mar. 2025
  Scientific journal, Abstract
  
  Magnesium is a macro-nutrient for all living organisms, and its stable isotope ratios (δ²⁶Mg) can be used for analyzing feeding habits and the dynamics of elements within the body. However, it was still unclear what kind of conditions for feeding and the surrounding seawater affect the Mg isotope ratios of marine fish. In this study, we report on the Mg isotopic composition of different organs of three fish species, blue mackerel (Scomber australasicus), black rockfish (Sebastes schlegeli), and Pacific bluefin tuna (Thunnus orientalis), as well as the magnitude of isotopic fractionation associated with Mg uptake in one-year-old T. orientalis. By using a delipidation treatment before acid samples digestion, the δ²⁶Mg value of each organ was compared before and after removing the lipids and body fluids. In T. orientalis and S. schlegel, the δ²⁶Mg of muscle and most internal organs is similar, whereas gills, fins, and bones are often 0.5‰ lower than the internal organs. We examined the variation in δ²⁶Mg values for each organ using multiple T. orientalis individuals, and found that muscle tissue showed the least variable values among individuals. The δ²⁶Mg of blood of one-year-old T. orientalis was clearly lower than the seawater value, and the value was close to that of its feed. This is thought to be the results that Mg²⁺ in seawater and blood plasma are separated each other in order to regulate osmotic pressure, and the contribution of Mg derived from feed is high. Isotopic fractionation of -0.40‰ was observed between the muscle of one-year-old T. orientalis and formula feed, similar to a cellular isotope fractionation between methanogen Methanothermobacter marburgensis and incubation medium. This is thought to reflect the selectivity of Mg uptake into the cell via membrane proteins.
• Highly effective energy transfer in the autotroph-heterotroph symbiosis: insights from compound-specific isotope analysis of amino acids
  Jincen Li; Mio Shibuya; Yuko Takizawa; Yoshito Chikaraishi
  PROGRESS IN EARTH AND PLANETARY SCIENCE, 12, 1, 10 Feb. 2025
  English, Scientific journal
• A large elevation in ¹⁵N/¹⁴N of collagenous amino acids: an insight from starvation experiments of marine organisms
  Hyuntae Choi; Yuko Takizawa; Nayeon Park; Yoshito Chikaraishi
  PROGRESS IN EARTH AND PLANETARY SCIENCE, 12, 1, 05 Feb. 2025
  English, Scientific journal
• Differential use of multiple food sources at a bathyal benthic ecosystem in the central Sagami Bay revealed by amino acid nitrogen isotopic compositions
  Hidetaka Nomaki; Yoshito Chikaraishi; Nanako O. Ogawa; Koh Maki; Motohiro Shimanaga; Hisami Suga; Masashi Tsuchiya; Toshi Nagata; Naohiko Ohkouchi
  Progress in Earth and Planetary Science, 12, 1, Springer Science and Business Media LLC, 15 Jan. 2025
  Scientific journal, Abstract
  
  The nitrogen isotopic composition (δ ¹⁵N) of amino acids can be used to estimate the trophic position of organisms with high precision compared to bulk tissue analyses, and shed light on potential food sources and food webs. Sagami Bay, Japan, is located at the tectonic plate boundary and have complex bottom topography, making multiple sources of organic matter to bathyal deep-sea ecosystems. Here, we applied this method to benthic animals (meiofauna, macrofauna, and megafauna) living at 1430 m deep in the central Sagami Bay, Japan. The δ ¹⁵N value of phenylalanine (δ ¹⁵N_Phe) reflects the value of primary producers and was used to estimate the food sources of organisms, while the difference between δ ¹⁵N value of glutamic acid (δ ¹⁵N_Glu) and δ ¹⁵N_Phe shifts between food source and consumer and was thus used to estimate the trophic position (TP_Glu/Phe). The data obtained were interpreted together with previously reported values from benthic foraminifera of the same site for a holistic understanding of the food web. The trophic positions of organisms from the central Sagami Bay ranged mostly from 2.2 to 3.6, except hydrozoans (up to 4.3). Organisms with similar bulk tissue δ ¹⁵N values sometimes exhibited different TP_Glu/Phe values. The observed δ¹⁵N_Phe varied greatly among benthic organisms in the central Sagami Bay (− 8.3‰ to 21.1‰), suggesting a wide variety of food sources exhibiting different δ¹⁵N_Phe values. Given the location of the study site at the central part of the deep basin, various organic matter from terrestrial, planktic, coastal, upper bathyal, and perhaps chemosynthetic origins can be expected to accumulate and become available for bathyal benthic organisms. Furthermore, the cross-plot of δ¹⁵N_Phe values and bulk tissue δ ¹³C values, another indicator of food source, suggested that macro–megafauna examined rely on different organic matter than metazoan meiofauna and foraminifera, which rely on particulate organic matter and bulk sediments. Despite living in the same habitat, organisms of these two size classes may belong to independent food webs due to differences in feeding ecology.
• Primordial aqueous alteration recorded in water-soluble organic molecules from the carbonaceous asteroid (162173) Ryugu
  Yoshinori Takano; Hiroshi Naraoka; Jason P. Dworkin; Toshiki Koga; Kazunori Sasaki; Hajime Sato; Yasuhiro Oba; Nanako O. Ogawa; Toshihiro Yoshimura; Kenji Hamase; Naohiko Ohkouchi; Eric T. Parker; José C. Aponte; Daniel P. Glavin; Yoshihiro Furukawa; Junken Aoki; Kuniyuki Kano; Shin-ichiro M. Nomura; Francois-Regis Orthous-Daunay; Philippe Schmitt-Kopplin; Aogu Furusho; Minako Hashiguchi; Kazuhiko Fukushima; Dan Aoki; Hannah L. McLain; Jamie E. Elsila; Heather V. Graham; John M. Eiler; Norbert Hertkorn; Alexander Ruf; Cédric Wolters; Junko Isa; Véronique Vuitton; Roland Thissen; Saburo Sakai; Haruna Sugahara; Hajime Mita; Yoshito Chikaraishi; Takaaki Yoshikawa; Satoru Tanaka; Mayu Morita; Morihiko Onose; Daisuke Araoka; Fumie Kabashima; Kosuke Fujishima; Hajime Sato; Tomoya Yamazaki; Yuki Kimura; Hisayoshi Yurimoto; Tomoki Nakamura; Takaaki Noguchi; Ryuji Okazaki; Hikaru Yabuta; Kanako Sakamoto; Toru Yada; Masahiro Nishimura; Aiko Nakato; Akiko Miyazaki; Kasumi Yogata; Masanao Abe; Tatsuaki Okada; Tomohiro Usui; Makoto Yoshikawa; Takanao Saiki; Satoshi Tanaka; Fuyuto Terui; Satoru Nakazawa; Sei-ichiro Watanabe; Yuichi Tsuda; Shogo Tachibana
  Nature Communications, 15, 1, Springer Science and Business Media LLC, 10 Jul. 2024
  Scientific journal, Abstract
  
  We report primordial aqueous alteration signatures in water-soluble organic molecules from the carbonaceous asteroid (162173) Ryugu by the Hayabusa2 spacecraft of JAXA. Newly identified low-molecular-weight hydroxy acids (HO-R-COOH) and dicarboxylic acids (HOOC-R-COOH), such as glycolic acid, lactic acid, glyceric acid, oxalic acid, and succinic acid, are predominant in samples from the two touchdown locations at Ryugu. The quantitative and qualitative profiles for the hydrophilic molecules between the two sampling locations shows similar trends within the order of ppb (parts per billion) to ppm (parts per million). A wide variety of structural isomers, including α- and β-hydroxy acids, are observed among the hydrophilic molecules. We also identify pyruvic acid and dihydroxy and tricarboxylic acids, which are biochemically important intermediates relevant to molecular evolution, such as the primordial TCA (tricarboxylic acid) cycle. Here, we find evidence that the asteroid Ryugu samples underwent substantial aqueous alteration, as revealed by the presence of malonic acid during keto–enol tautomerism in the dicarboxylic acid profile. The comprehensive data suggest the presence of a series for water-soluble organic molecules in the regolith of Ryugu and evidence of signatures in coevolutionary aqueous alteration between water and organics in this carbonaceous asteroid.
• Enantioselective three-dimensional high-performance liquid chromatographic determination of amino acids in the Hayabusa2 returned samples from the asteroid Ryugu
  Aogu Furusho; Chiharu Ishii; Takeyuki Akita; Mai Oyaide; Masashi Mita; Hiroshi Naraoka; Yoshinori Takano; Jason P. Dworkin; Yasuhiro Oba; Toshiki Koga; Kazuhiko Fukushima; Dan Aoki; Minako Hashiguchi; Hajime Mita; Yoshito Chikaraishi; Naohiko Ohkouchi; Nanako O. Ogawa; Saburo Sakai; Daniel P. Glavin; Jamie E. Elsila; Eric T. Parker; José C. Aponte; Hannah L. McLain; Francois Regis Orthous-Daunay; Véronique Vuitton; Roland Thissen; Cédric Wolters; Philippe Schmitt-Kopplin; Alexander Ruf; Junko Isa; Norbert Hertkorn; John M. Eiler; Toshihiro Yoshimura; Haruna Sugahara; Heather V. Graham; Yoshihiro Furukawa; Daisuke Araoka; Satoru Tanaka; Takaaki Yoshikawa; Fumie Kabashima; Kazunori Sasaki; Hajime Sato; Tomoya Yamazaki; Morihiko Onose; Mayu Morita; Yuki Kimura; Kuniyuki Kano; Junken Aoki; Kosuke Fujishima; Shin ichiro Nomura; Shogo Tachibana; Tomoki Nakamura; Takaaki Noguchi; Ryuji Okazaki; Hikaru Yabuta; Hisayoshi Yurimoto; Kanako Sakamoto; Toru Yada; Masahiro Nishimura; Aiko Nakato; Akiko Miyazaki; Kasumi Yogata; Masanao Abe; Tomohiro Usui; Makoto Yoshikawa; Takanao Saiki; Satoshi Tanaka; Fuyuto Terui; Satoru Nakazawa; Tatsuaki Okada; Sei ichiro Watanabe; Yuichi Tsuda; Kenji Hamase
  Journal of Chromatography Open, 5, May 2024
  Scientific journal
• Nitrogen K-edge X-ray adsorption near-edge structure spectroscopy of chemically adsorbed ammonia gas on clay minerals and the 15N/14N-nitrogen isotopic fractionation.
  Haruna Sugahara; Toshihiro Yoshimura; Yusuke Tamenori; Yoshinori Takano; Nanako O Ogawa; Yoshito Chikaraishi; Naohiko Ohkouchi
  Analytical sciences : the international journal of the Japan Society for Analytical Chemistry, 05 Feb. 2024, [International Magazine]
  English, Scientific journal, Ammonia (NH3) is a simple and essential nitrogen carrier in the universe. Its adsorption on mineral surfaces is an important step in the synthesis of nitrogenous organic molecules in extraterrestrial environments. The nitrogen isotopic ratios provide a useful tool for understanding the formation processes of N-bearing molecules. In this study, adsorption experiments were conducted using gaseous NH3 and representative clay minerals. The strongly adsorbed NH3 was 15N-enriched in a state of chemical equilibrium between the adsorption and desorption on the siliceous host surface. The nitrogen K-edge X-ray adsorption near-edge structure spectroscopy study revealed that these initial ammonia gases were chemically adsorbed as ammonium ions (NH4+) on clay minerals.
• Development of a rapid and highly accurate method for 13C tracer-based metabolomics and its application on a hydrogenotrophic methanogen.
  Yuto Fukuyama; Shigeru Shimamura; Sanae Sakai; Yuta Michimori; Tomomi Sumida; Yoshito Chikaraishi; Haruyuki Atomi; Takuro Nunoura
  ISME communications, 4, 1, ycad006, Jan. 2024, [International Magazine]
  English, Scientific journal, Microfluidic capillary electrophoresis-mass spectrometry (CE-MS) is a rapid and highly accurate method to determine isotopomer patterns in isotopically labeled compounds. Here, we developed a novel method for tracer-based metabolomics using CE-MS for underivatized proteinogenic amino acids. The method consisting of a ZipChip CE system and a high-resolution Orbitrap Fusion Tribrid mass spectrometer allows us to obtain highly accurate data from 1 μl of 100 nmol/l amino acids comparable to a mere 1 [Formula: see text] 104-105 prokaryotic cells. To validate the capability of the CE-MS method, we analyzed 16 protein-derived amino acids from a methanogenic archaeon Methanothermobacter thermautotrophicus as a model organism, and the mass spectra showed sharp peaks with low mass errors and background noise. Tracer-based metabolome analysis was then performed to identify the central carbon metabolism in M. thermautotrophicus using 13C-labeled substrates. The mass isotopomer distributions of serine, aspartate, and glutamate revealed the occurrence of both the Wood-Ljungdahl pathway and an incomplete reductive tricarboxylic acid cycle for carbon fixation. In addition, biosynthesis pathways of 15 amino acids were constructed based on the mass isotopomer distributions of the detected protein-derived amino acids, genomic information, and public databases. Among them, the presence of alternative enzymes of alanine dehydrogenase, ornithine cyclodeaminase, and homoserine kinase was suggested in the biosynthesis pathways of alanine, proline, and threonine, respectively. To our knowledge, the novel 13C tracer-based metabolomics using CE-MS can be considered the most efficient method to identify central carbon metabolism and amino acid biosynthesis pathways and is applicable to any kind of isolated microbe.
• Chemical evolution of primordial salts and organic sulfur molecules in the asteroid 162173 Ryugu
  Toshihiro Yoshimura; Yoshinori Takano; Hiroshi Naraoka; Toshiki Koga; Daisuke Araoka; Nanako O. Ogawa; Philippe Schmitt-Kopplin; Norbert Hertkorn; Yasuhiro Oba; Jason P. Dworkin; Jose C. Aponte; Takaaki Yoshikawa; Satoru Tanaka; Naohiko Ohkouchi; Minako Hashiguchi; Hannah Mclain; Eric T. Parker; Saburo Sakai; Mihoko Yamaguchi; Takahiro Suzuki; Tetsuya Yokoyama; Hisayoshi Yurimoto; Tomoki Nakamura; Takaaki Noguchi; Ryuji Okazaki; Hikaru Yabuta; Kanako Sakamoto; Toru Yada; Masahiro Nishimura; Aiko Nakato; Akiko Miyazaki; Kasumi Yogata; Masanao Abe; Tatsuaki Okada; Tomohiro Usui; Makoto Yoshikawa; Takanao Saiki; Satoshi Tanaka; Fuyuto Terui; Satoru Nakazawa; Sei-ichiro Watanabe; Yuichi Tsuda; Shogo Tachibana; Kenji Hamase; Aogu Furusho; Kazuhiko Fukushima; Dan Aoki; Daniel P. Glavin; Hannah L. Mclain; Jamie E. Elsila; Heather V. Graham; John M. Eiler; Alexander Ruf; Francois-Regis Orthous-Daunay; Cedric Wolters; Junko Isa; Mayu Morita; Veronique Vuitton; Roland Thissen; Shin-ichiro M. Nomura; Haruna Sugahara; Hajime Mita; Yoshihiro Furukawa; Yoshito Chikaraishi; Morihiko Onose; Fumie Kabashima; Kosuke Fujishima; Hajime Sato; Kazunori Sasaki; Kuniyuki Kano; Junken Aoki; Tomoya Yamazaki; Yuki Kimura
  NATURE COMMUNICATIONS, 14, 1, 18 Sep. 2023
  English, Scientific journal
• Soluble organic molecules in samples of the carbonaceous asteroid (162173) Ryugu
  Hiroshi Naraoka; Yoshinori Takano; Jason P. Dworkin; Yasuhiro Oba; Kenji Hamase; Aogu Furusho; Nanako O. Ogawa; Minako Hashiguchi; Kazuhiko Fukushima; Dan Aoki; Philippe Schmitt-Kopplin; José C. Aponte; Eric T. Parker; Daniel P. Glavin; Hannah L. McLain; Jamie E. Elsila; Heather V. Graham; John M. Eiler; Francois-Regis Orthous-Daunay; Cédric Wolters; Junko Isa; Véronique Vuitton; Roland Thissen; Saburo Sakai; Toshihiro Yoshimura; Toshiki Koga; Naohiko Ohkouchi; Yoshito Chikaraishi; Haruna Sugahara; Hajime Mita; Yoshihiro Furukawa; Norbert Hertkorn; Alexander Ruf; Hisayoshi Yurimoto; Tomoki Nakamura; Takaaki Noguchi; Ryuji Okazaki; Hikaru Yabuta; Kanako Sakamoto; Shogo Tachibana; Harold C. Connolly; Dante S. Lauretta; Masanao Abe; Toru Yada; Masahiro Nishimura; Kasumi Yogata; Aiko Nakato; Miwa Yoshitake; Ayako Suzuki; Akiko Miyazaki; Shizuho Furuya; Kentaro Hatakeda; Hiromichi Soejima; Yuya Hitomi; Kazuya Kumagai; Tomohiro Usui; Tasuku Hayashi; Daiki Yamamoto; Ryota Fukai; Kohei Kitazato; Seiji Sugita; Noriyuki Namiki; Masahiko Arakawa; Hitoshi Ikeda; Masateru Ishiguro; Naru Hirata; Koji Wada; Yoshiaki Ishihara; Rina Noguchi; Tomokatsu Morota; Naoya Sakatani; Koji Matsumoto; Hiroki Senshu; Rie Honda; Eri Tatsumi; Yasuhiro Yokota; Chikatoshi Honda; Tatsuhiro Michikami; Moe Matsuoka; Akira Miura; Hirotomo Noda; Tetsuya Yamada; Keisuke Yoshihara; Kosuke Kawahara; Masanobu Ozaki; Yu-ichi Iijima; Hajime Yano; Masahiko Hayakawa; Takahiro Iwata; Ryudo Tsukizaki; Hirotaka Sawada; Satoshi Hosoda; Kazunori Ogawa; Chisato Okamoto; Naoyuki Hirata; Kei Shirai; Yuri Shimaki; Manabu Yamada; Tatsuaki Okada; Yukio Yamamoto; Hiroshi Takeuchi; Atsushi Fujii; Yuto Takei; Kento Yoshikawa; Yuya Mimasu; Go Ono; Naoko Ogawa; Shota Kikuchi; Satoru Nakazawa; Fuyuto Terui; Satoshi Tanaka; Takanao Saiki; Makoto Yoshikawa; Sei-ichiro Watanabe; Yuichi Tsuda
  Science, 379, 6634, American Association for the Advancement of Science (AAAS), 24 Feb. 2023
  Scientific journal, The Hayabusa2 spacecraft collected samples from the surface of the carbonaceous near-Earth asteroid (162173) Ryugu and brought them to Earth. The samples were expected to contain organic molecules, which record processes that occurred in the early Solar System. We analyzed organic molecules extracted from the Ryugu surface samples. We identified a variety of molecules containing the atoms CHNOS, formed by methylation, hydration, hydroxylation, and sulfurization reactions. Amino acids, aliphatic amines, carboxylic acids, polycyclic aromatic hydrocarbons, and nitrogen-heterocyclic compounds were detected, which had properties consistent with an abiotic origin. These compounds likely arose from an aqueous reaction on Ryugu’s parent body and are similar to the organics in Ivuna-type meteorites. These molecules can survive on the surfaces of asteroids and be transported throughout the Solar System.
• Trophic niche separation of two non-spinose planktonic foraminifers Neogloboquadrina dutertrei and Pulleniatina obliquiloculata
  Ryuji Toue; Kazuhiko Fujita; Masashi Tsuchiya; Yoshito Chikaraishi; Yoko Sasaki; Naohiko Ohkouchi
  Progress in Earth and Planetary Science, 9, 1, Springer Science and Business Media LLC, Dec. 2022
  Scientific journal, Abstract
  
  Based on laboratory observations, planktonic foraminifers are omnivorous, feeding zooplankton and phytoplankton. Spinose species tend toward greater dependence on zooplankton prey than on phytoplankton prey, while non-spinose species are more adapted to herbivorous diets. However, the trophic activity of planktonic foraminifers in the natural environment and their trophic positions in the marine food web have not yet been fully understood. The trophic position (TP) of two non-spinose species, Neogloboquadrina dutertrei and Pulleniatina obliquiloculata, was determined by differences in the nitrogen isotopic composition between two amino acids (glutamic acid and phenylalanine). Results show that TP values of N. dutertrei were ~ 2.4, indicating dependence on omnivorous (mixed herbivorous and carnivorous) diets, while those of P. obliquiloculata were ~ 2.1, indicating dependence on herbivorous diets. Together with previous laboratory observations, these TP values suggest that N. dutertrei is a detritivore or scavenger, while P. obliquiloculata is generally a herbivore. This trophic niche separation likely allows these two planktonic foraminiferal species to live within a similar depth zone in the open water column and provides a clue for understanding causes of spatial and temporal changes in their relative abundances in living and sediment assemblages.
• Using geostatistical analysis for simultaneous estimation of isoscapes and ontogenetic shifts in isotope ratios of highly migratory marine fish
  Jun Matsubayashi; Katsuya Kimura; Naohiko Ohkouchi; Nanako O. Ogawa; Naoto F. Ishikawa; Yoshito Chikaraishi; Yuichi Tsuda; Hiroshi Minami
  Frontiers in Marine Science, 9, Frontiers Media SA, 28 Nov. 2022
  Scientific journal, Tracking migration of highly migratory marine fish using isotope analysis (iso-logging) has become a promising tool in recent years. However, application of this method is often hampered by the lack of essential information such as spatial variations in isotope ratios across habitats (isoscapes) and ontogenetic shifts of isotope ratios of target animals. Here, we test the utility of geostatistical analysis to generate isoscapes of δ¹³C and δ¹⁵N in the western Pacific and estimate the ontogenetic shifts in δ¹³C and δ¹⁵N values of a target species. We first measured δ¹³C and δ¹⁵N in the white muscle of juvenile (n = 210) and adult (n = 884) skipjack tuna Katsuwonus pelamis sampled across the northwest Pacific. Next we fitted a geostatistical model to account for the observed spatial variations in δ¹³C and δ¹⁵N of skipjack by fork length and other environmental variables with spatial random effects. We then used the best-fit models to predict the isoscapes of δ¹³C and δ¹⁵N in 2021. Furthermore, we measured δ¹⁵N of amino acids (δ¹⁵N_AAs) of skipjack (n = 5) to determine whether the observed spatial variation of isotope ratios resulted from baseline shifts or differences in trophic position. The geostatistical model reasonably estimated both isoscapes and ontogenetic shifts from isotope ratios of skipjack, and the isoscapes showed that δ¹³C and δ¹⁵N can clearly distinguish the latitudinal migration of skipjack in the western Pacific. The δ¹⁵N_AAs supported the results of the geostatistical model, that is, observed variations in skipjack δ¹⁵N were largely derived from a baseline shift rather than regional differences in trophic position. Thus, we showed that geostatistical analysis can provide essential basic information required for iso-logging without compound-specific isotope analysis.
• Nitrogen Isotopes of Sinking Particles Reveal the Seasonal Transition of the Nitrogen Source for Phytoplankton
  Chisato Yoshikawa; Nanako O. Ogawa; Yoshito Chikaraishi; Akiko Makabe; Yohei Matsui; Yoshikazu Sasai; Masahide Wakita; Makio C. Honda; Yoshihisa Mino; Maki N. Aita; Tetsuichi Fujiki; Takuro Nunoura; Naomi Harada; Naohiko Ohkouchi
  Geophysical Research Letters, 49, 17, American Geophysical Union (AGU), 16 Sep. 2022
  Scientific journal
• Integrative assessment of amino acid nitrogen isotontegrative assessment of amino acid nitrogen isotopic composition in biological tissue samples determined by GC/C/IRMS, LC × EA/IRMS, and LC × GC/C/IRMS
  Naoto F. Ishikawa; Nanako O. Ogawa; Yuchen Sun; Yoshito Chikaraishi; Yoshinori Takano; Naohiko Ohkouchi
  Limnology and Oceanography: Methods, Wiley, 19 Jul. 2022, [Peer-reviewed]
  English, Scientific journal
• Discovery of a colossal slickhead (Alepocephaliformes: Alepocephalidae): an active-swimming top predator in the deep waters of Suruga Bay, Japan
  Yoshihiro Fujiwara; Masaru Kawato; Jan Yde Poulsen; Hitoshi Ida; Yoshito Chikaraishi; Naohiko Ohkouchi; Kazumasa Oguri; Shinpei Gotoh; Genki Ozawa; Sho Tanaka; Masaki Miya; Tetsuya Sado; Katsunori Kimoto; Takashi Toyofuku; Shinji Tsuchida
  Scientific Reports, 11, 1, Springer Science and Business Media LLC, Dec. 2021
  Scientific journal, A novel species of the family Alepocephalidae (slickheads), Narcetes shonanmaruae, is described based on four specimens collected at depths greater than 2171 m in Suruga Bay, Japan. Compared to other alepocephalids, this species is colossal (reaching ca. 140 cm in total length and 25 kg in body weight) and possesses a unique combination of morphological characters comprising anal fin entirely behind the dorsal fin, multiserial teeth on jaws, more scale rows than congeners, precaudal vertebrae less than 30, seven branchiostegal rays, two epurals, and head smaller than those of relatives. Mitogenomic analyses also support the novelty of this large deep-sea slickhead. Although most slickheads are benthopelagic or mesopelagic feeders of gelatinous zooplankton, behavioural observations and dietary analyses indicate that the new species is piscivorous. In addition, a stable nitrogen isotope analysis of specific amino acids showed that N. shonanmaruae occupies one of the highest trophic positions reported from marine environments to date. Video footage recorded using a baited camera deployed at a depth of 2572 m in Suruga Bay revealed the active swimming behaviour of this slickhead. The scavenging ability and broad gape of N. shonanmaruae might be correlated with its colossal body size and relatively high trophic position.
• Redox-Controlled Ammonium Storage and Overturn in Ediacaran Oceans
  Christian Hallmann; Emmanuelle Grosjean; Nathan D. Shapiro; Yuichiro Kashiyama; Yoshito Chikaraishi; David A. Fike; Naohiko Ohkouchi; Roger E. Summons
  Frontiers in Earth Science, 9, Frontiers Media S.A., 10 Sep. 2021
  English, Scientific journal
• Influences of Ocean Currents on the Diets of Demersal Fish Communities in the Western North Pacific Revealed by Their Muscle Carbon and Nitrogen Isotopic Compositions
  Naoto F. Ishikawa; Nanako O. Ogawa; Yoshito Chikaraishi; Moto-omi Yamaguchi; Katsunori Fujikura; Yosuke Miyairi; Yusuke Yokoyama; Toshi Nagata; Naohiko Ohkouchi
  Frontiers in Marine Science, 8, Frontiers Media SA, 05 May 2021
  Scientific journal, To study the influence of different ocean currents on the trophic spectra found in a sympatric fish community, we analyzed the radiocarbon contents (Δ¹⁴C) and stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopic compositions in their bulk muscle tissues and the δ¹⁵N of individual amino acids in 26 species of demersal fish collected from off Tohoku (Pacific coast), northeastern Japan. The Δ¹⁴C values of the fish varied from –42 to +41‰, consistent with the Δ¹⁴C of the dissolved inorganic carbon in the cold Oyashio Current (typically about –50‰) and the warm Kuroshio Current (typically about +50‰). The trophic positions (TPs) of the fish estimated from the δ¹⁵N values of amino acids increased from 3.1 to 4.5 with increasing snout length. A negative correlation was observed between Δ¹⁴C and TP in gadiform fish and flatfish, suggesting that the Oyashio Current delivers a high TP diet to these fish groups. These results suggest that the trophic ecology of marine fish in the coastal western North Pacific is primarily controlled by the two major surface water currents, but is also significantly influenced by a combination of species-specific feeding and migration strategies.
• Synthesis of 13C-enriched amino acids with 13C-depleted insoluble organic matter in a formose-type reaction in the early solar system
  Yoshihiro Furukawa; Yoshinari Iwasa; Yoshito Chikaraishi
  Science Advances, 7, eabd3575, Apr. 2021, [Peer-reviewed]
  Scientific journal
• A new insight into isotopic fractionation associated with decarboxylation in organisms: implications for amino acid isotope approaches in biogeoscience
  Yuko Takizawa; Yoshinori Takano; Bohyung Choi; Prarthana S. Dharampal; Shawn A. Steffan; Nanako O. Ogawa; Naohiko Ohkouchi; Yoshito Chikaraishi
  Progress in Earth and Planetary Science, 7, 1, Springer Science and Business Media LLC, Dec. 2020
  Scientific journal,
  Stable nitrogen (¹⁵N/¹⁴N) and carbon (¹³C/¹²C) isotopic compositions of amino acids in organisms have widely been employed as a powerful tool to evaluate resource utilization and trophic connection among organisms in diverse ecosystems. However, little is known about the physiological factors or mechanisms responsible for determining the isotopic discrimination (particularly for carbon) within amino acids of organisms. In the present study, we investigated the inter-trophic discrimination of nitrogen and carbon isotopes within amino acids (Δδ¹⁵N_AA and Δδ¹³C_AA, respectively) using four consumer–diet pairs. Each pairing illustrates a metabolic perspective of isotopic fractionation of amino acids. The Δδ¹⁵N_AA values in these combinations reveal a trend consistent with those observed in many other combinations in previous studies. This further validates a standard scenario: the deamination preferentially removes ¹⁴N amino group from diet-derived amino acids, leaving behind the ¹⁵N-enriched amino acids in consumer biomass. The Δδ¹⁵N_AA values thus mirror the activity of amino acid deamination in consumers. In contrast, the trends in the Δδ¹³C_AA value suggest a different metabolic fate for the amino acid carbon isotope. Based on our results, we predict the following scenario: decarboxylation preferentially removes ¹²C α-carbon (i.e., carbonyl-carbon) from pyruvic acid in glycolysis, and from α-ketoglutaric acid in the tricarboxylic acid cycle, leaving behind the ¹³C-enriched both pyruvic and α-ketoglutaric acids. The ¹³C is then transferred to amino acids that are synthesized from the ¹³C-enriched precursor molecules within consumers. The Δδ¹³C_AA values therefore mirror the pathways of de novo amino acid synthesis in consumers. The proposed link between nitrogen and carbon isotopes can refine our knowledge of the potential processes affecting the isotopic fractionation within diet and consumer compartments, as well as environmental samples.
  
  
  
  Graphical abstract
• Seasonality of decadal-scale trophic declines and nutrient regime shifts in the Laysan albatross and Newell's shearwater
  Kaycee E. Morra; Yoshito Chikaraishi; Helen F. James; Sam Rossman; Anne E. Wiley; Peggy H. Ostrom
  Marine Ecology Progress Series, 654, 163, 175, Inter-Research, 12 Nov. 2020
  English, Scientific journal
• Trophic response to ecological conditions of habitats: Evidence from trophic variability of freshwater fish
  Bohyung Choi; Changhwa Lee; Yuko Takizawa; Yoshito Chikaraishi; Hye-Ji Oh; Kwang-Hyeon Chang; Min-Ho Jang; Hyun-Woo Kim; Kyung-Lak Lee; Kyung-Hoon Shin
  Ecology and Evolution, 10, 14, 7250, 7260, John Wiley and Sons Ltd, 01 Jul. 2020
  English, Scientific journal
• Trophic hierarchy of coastal marine fish communities viewed via compound-specific isotopic analysis of amino acids
  D Xing; B Choi; Y Takizawa; R Fan; S Sugaya; M Tuchiya; N Ohkouchi; Y Chikaraishi
  Marine Ecology Progress Series, Inter-Research Science Center, 2020
  Scientific journal
• Quantifying niche partitioning and multichannel feeding among tree squirrels
  Jonathan N. Pauli; Philip J. Manlick; Prarthana S. Dharampal; Yuko Takizawa; Yoshito Chikaraishi; Laura J. Niccolai; Jennifer A. Grauer; Kristina L. Black; Mario Garces Restrepo; Paula L. Perrig; Evan C. Wilson; Marie E. Martin; Mauriel Rodriguez Curras; Tiffany A. Bougie; Kimberly L. Thompson; Matthew M. Smith; Shawn A. Steffan
  Food Webs, 21, Elsevier Inc., 01 Dec. 2019
  English, Scientific journal
• Extraterrestrial ribose and other sugars in primitive meteorites.
  Furukawa Y; Chikaraishi Y; Ohkouchi N; Ogawa N; Glavin D. P; Dworkin J. P; Abe C; Nakamura T
  PNAS, 116, 24440, 24445, Nov. 2019, [Peer-reviewed]
• Strong correspondence between nitrogen isotope composition of foliage and chlorin across a rainfall gradient: Implications for paleo-reconstruction of the nitrogen cycle
  Sara K.E. Goulden; Naohiko Ohkouchi; Katherine H. Freeman; Yoshito Chikaraishi; Nanako O. Ogawa; Hisami Suga; Oliver Chadwick; Benjamin Z. Houlton
  Biogeosciences, 16, 19, 3869, 3882, Copernicus GmbH, 08 Oct. 2019
  English, Scientific journal
• Development of a Purification Method for Compound Specific Carbon Isotope Analysis of Phytosterols and Long-chain n-fatty Acids in Higher Plants
  Takeuchi Riko; Chikaraishi Yoshito; Ogawa Nanako O; Furota Satoshi; Ohkouchi Naohiko; Aoki Motohide; Uchida Tatsuya; Umemura Tomonari; Kumata Hidetoshi
  BUNSEKI KAGAKU, 68, 5, 297, 306, May 2019, [Peer-reviewed]
  Japanese
• Amino acid ¹⁵ N analysis reveals change in the importance of freshwater resources between the hunter-gatherer and farmer in the Neolithic upper Tigris
  Yu Itahashi; Yilmaz Selim Erdal; Halil Tekin; Lubna Omar; Yutaka Miyake; Yoshito Chikaraishi; Naohiko Ohkouchi; Minoru Yoneda
  American Journal of Physical Anthropology, 168, 4, 676, 686, Apr. 2019, [Peer-reviewed]
  Scientific journal
• Trophic declines and decadal-scale foraging segregation in three pelagic seabirds
  Morra Kaycee E; Chikaraishi Yoshito; Gandhi Hasand; James Helen F; Rossman Sam; Wiley Anne E; Raine Andre F; Beck Jessie; Ostrom Peggy H
  OECOLOGIA, 189, 2, 395, 406, Feb. 2019, [Peer-reviewed]
• Enhancing insights into foraging specialization in the world's largest fish using a multi-tissue, multi-isotope approach
  Alex S. J. Wyatt; Rui Matsumoto; Yoshito Chikaraishi; Yosuke Miyairi; Yusuke Yokoyama; Keiichi Sato; Nao Ohkouchi; Toshi Nagata
  ECOLOGICAL MONOGRAPHS, 89, 1, Feb. 2019, [Peer-reviewed]
  English, Scientific journal
• Remarkable fractionation of nitrogen isotopes in anaerobic amino acid metabolisms
  Y. Takizawa; Y. Chikaraishi
  29th International Meeting on Organic Geochemistry, IMOG 2019, European Association of Geoscientists and Engineers, EAGE, 2019
  English, International conference proceedings
• Illustrating food web structure in a marine ecosystem via compound-specific isotope analysis of amino acids
  D. Xing; Y. Chikaraishi
  29th International Meeting on Organic Geochemistry, IMOG 2019, European Association of Geoscientists and Engineers, EAGE, 2019
  English, International conference proceedings
• Amino acid N analysis reveals change in the importance of freshwater resources between the hunter-gatherer and farmer in the Neolithic upper Tigris
  Itahashi, Yu; Erdal, Yilmaz Selim; Tekin, Halil; Omar, Lubna; Miyake, Yutaka; Chikaraishi, Yoshito; Ohkouchi, Naohiko; Yoneda, Minoru
  American journal of physical anthropology, 168, 4, 676, 686, WILEY, Jan. 2019, [Peer-reviewed]
  English, Scientific journal, [OBJECTIVE] The inhabitants of several sites in the Upper Tigris Valley, such as Hakemi Use, domesticated animals and cereals during the Pottery Neolithic period, while the inhabitants in this valley were hunter-gatherers in the Pre-Pottery Neolithic period, consuming freshwater and terrestrial food resources. However, there is considerable uncertainty surrounding whether or not changes in dietary food composition accompanied the shift in food production away from foraging. In order to reveal the impact of the development of agriculture on the human diet over the Pre-Pottery and Pottery Neolithic periods in this region, we analyzed the isotopic compositions of amino acids from the farmers at the Hakemi Use Pottery Neolithic site, and compared them with those from the Pre-Pottery hunter-gatherers in the close region.
  [MATERIALS AND METHODS] Herein, we report the nitrogen isotopic compositions of amino acids, as well as both carbon and nitrogen isotopic compositions of bulk collagen, from human and faunal remains collected from Hakemi Use.
  [RESULTS] Whereas freshwater resources were consumed by hunter-gatherers in this region during the Pre-Pottery period, the δ N values of glutamic
• Molecular and isotopic compositions of nitrogen-containing organic molecules formed during UV-irradiation of simulated interstellar ice
  Haruna Sugahara; Yoshinori Takano; Shogo Tachibana; Iyo Sugawara; Yoshito Chikaraishi; Nanako O. Ogawa; Naohiko Ohkouchi; Akira Kouchi; Hisayoshi Yurimoto
  Geochemical Journal, 53, 1, 5, 20, 2019, [Peer-reviewed]
  Scientific journal
• 好熱性水素酸化細菌における始原的で可逆的なTCA回路
  Takuro NUNOURA; Yoshito CHIKARAISHI; Haruyuki ATOMI
  KAGAKU TO SEIBUTSU, 57, 1, 7, 9, Japan Society for Bioscience, Biotechnology, and Agrochemistry, 20 Dec. 2018
  Scientific journal
• Trophic structure and energy flow in a shallow-water hydrothermal vent: Insights from a stable isotope approach
  Chang Ni-Na; Lin Li-Hung; Tu Tzu-Hsuan; Jeng Ming-Shiou; Chikaraishi Yoshito; Wang Pei-Ling
  PLOS ONE, 13, 10, 17 Oct. 2018, [Peer-reviewed]
• Insight into anaerobic methanotrophy from C-13/C-12- amino acids and C-14/C-12-ANME cells in seafloor microbial ecology
  Takano Yoshinori; Chikaraishi Yoshito; Imachi Hiroyuki; Miyairi Yosuke; Ogawa Nanako O; Kaneko Masanori; Yokoyama Yusuke; Krueger Martin; Ohkouchi Naohiko
  SCIENTIFIC REPORTS, 8, 24 Sep. 2018, [Peer-reviewed]
• A new analytical method for determination of the nitrogen isotopic composition of methionine: Its application to aquatic ecosystems with mixed resources
  Ishikawa Naoto F; Chikaraishi Yoshito; Takano Yoshinori; Sasaki Yoko; Takizawa Yuko; Tsuchiya Masashi; Tayasu Ichiro; Nagata Toshi; Ohkouchi Naohiko
  LIMNOLOGY AND OCEANOGRAPHY-METHODS, 16, 9, 607, 620, Sep. 2018, [Peer-reviewed]
  Scientific journal
• Compound-specific isotope analysis of benthic foraminifer amino acids suggests microhabitat variability in rocky-shore environments
  Tsuchiya Masashi; Chikaraishi Yoshito; Nomaki Hidetaka; Sasaki Yoko; Tame Akihiro; Uematsu Katsuyuki; Ohkouchi Naohiko
  ECOLOGY AND EVOLUTION, 8, 16, 8380, 8395, Aug. 2018, [Peer-reviewed]
• Compound-specific isotope analysis of benthic foraminifer amino acids suggests microhabitat variability in rocky-shore environments
  Tsuchiya M; Chikaraishi Y; Nomaki H; Sasaki Y; Tame A; Uematsu K; Ohkouchi N
  Ecology and Evolution, 00, 1, 16, Jul. 2018, [Peer-reviewed]
  English, Scientific journal
• Reply to “Comment on “Ecological niche of Neanderthals from Spy Cave revealed by nitrogen isotopes of individual amino acids in collagen.” [J. Hum. Evol. 93 (2016) 82–90]” [J. Hum. Evol. 117 (2018) 53–55]
  Yuichi I. Naito; Yoshito Chikaraishi; Dorothée G. Drucker; Naohiko Ohkouchi; Patrick Semal; Christoph Wißing; Hervé Bocherens
  Journal of Human Evolution, 117, 56, 60, 01 Apr. 2018, [Peer-reviewed]
  English
• A primordial and reversible TCA cycle in a facultatively chemolithoautotrophic thermophile.
  Takuro Nunoura; Yoshito Chikaraishi; Rikihisa Izaki; Takashi Suwa; Takaaki Sato; Takeshi Harada; Koji Mori; Yumiko Kato; Masayuki Miyazaki; Shigeru Shimamura; Katsunori Yanagawa; Aya Shuto; Naohiko Ohkouchi; Nobuyuki Fujita; Yoshihiro Takaki; Haruyuki Atomi; Ken Takai
  Science (New York, N.Y.), 359, 6375, 559, 563, 02 Feb. 2018, [Peer-reviewed], [International Magazine]
  English
• Dining together: Reconstruction of Neolithic food consumption based on the δ¹⁵N values for individual amino acids at Tell el-Kerkh, northern Levant
  Yu Itahashi; Akira Tsuneki; Sean P. Dougherty; Yoshito Chikaraishi; Naohiko Ohkouchi; Minoru Yoneda
  Journal of Archaeological Science: Reports, 17, 775, 784, Feb. 2018, [Peer-reviewed]
  Scientific journal
• Spatiotemporal changes in sunken debris off Miyagi after the 2011 off the Pacific coast of Tohoku Earthquake using information on debris collected by bottom trawls
  Yoshihiro Fujiwara; Yoshimi Takahashi; Natsumi Kasai; Takafumi Kasaya; Takehisa Yamakita; Shinji Tsuchida; Masaru Kawato; Hiroshi Kitazato; Katsunori Fujikura
  NIPPON SUISAN GAKKAISHI, 84, 5, 885, 888, 2018, [Peer-reviewed]
  Japanese, Scientific journal
• Historical niche partitioning and long-term trophic shifts in Laurentian Great Lakes deepwater coregonines
  Chelsey Blanke; Yoshito Chikaraishi; M. Jake Vander Zanden
  Ecosphere, 9, 1, 01 Jan. 2018, [Peer-reviewed]
  English, Scientific journal
• Fractionation of stable nitrogen isotopes (15N/14N) during enzymatic deamination of glutamic acid: Implications for mass and energy transfers in the biosphere
  Akiko S. Goto; Kasumi Miura; Takashi Korenaga; Takashi Hasegawa; Naohiko Ohkouchi; Yoshito Chikaraishi
  Geochemical Journal, 52, 3, 273, 280, 2018, [Peer-reviewed]
  English, Scientific journal
• Polychlorinated biphenyls (PCBs) in deep-sea organisms and sediments off Tohoku after the Great East Japan Earthquake in 2011
  Ogawa Nanako O; Ohkouchi Naohiko; Nomaki Hidetaka; Chikaraishi Yoshito; Fujikura Katsunori; Kitazato Hiroshi
  NIPPON SUISAN GAKKAISHI, 84, 5, 897, 900, 2018, [Peer-reviewed]
• Algal-derived 24-ethylcholesta-5,22-dien-3 beta-ol (stigmasterol) is frequently found in high-molecular-weight dissolved organic matter (HMW-DOM) during summer in freshwater and brackish lakes
  Urai Atsushi; Takahashi Koji; Chikaraishi Yoshito; Fukushima Kazuo
  GEOCHEMICAL JOURNAL, 52, 6, E15, E20, 2018, [Peer-reviewed]
• Algal-derived 24-ethylcholesta-5,22-dien-3 beta-ol (stigmasterol) is frequently found in high-molecular-weight dissolved organic matter (HMW-DOM) during summer in freshwater and brackish lakes
  Urai Atsushi; Takahashi Koji; Chikaraishi Yoshito; Fukushima Kazuo
  GEOCHEMICAL JOURNAL, 52, 4, E15, E20, 2018, [Peer-reviewed]
• Change in the δ15N value of plant amino acids on the phenology of leaf flush and senescence
  Takizawa Yuko; Chikaraishi Yoshito
  Researches in Organic Geochemistry, 33, 1, 1, 6, Dec. 2017, [Peer-reviewed]
  English, Scientific journal
• Microbial Eukaryotes that Lack Sterols
  Kiyotaka Takishita; Yoshito Chikaraishi; Goro Tanifuji; Naohiko Ohkouchi; Tetsuo Hashimoto; Katsunori Fujikura; Andrew J. Roger
  JOURNAL OF EUKARYOTIC MICROBIOLOGY, 64, 6, 897, 900, Nov. 2017, [Peer-reviewed]
  English, Scientific journal
• Advances in the application of amino acid nitrogen isotopic analysis in ecological and biogeochemical studies
  Naohiko Ohkouchi; Yoshito Chikaraishi; Hilary G. Close; Brian Fry; Thomas Larsen; Daniel J. Madigan; Matthew D. McCarthy; Kelton W. McMahon; Toshi Nagata; Yuichi I. Naito; Nanako O. Ogawa; Brian N. Popp; Shawn Steffan; Yoshinori Takano; Ichiro Tayasu; Alex S. J. Wyatt; Yasuhiko T. Yamaguchi; Yusuke Yokoyama
  ORGANIC GEOCHEMISTRY, 113, 150, 174, Nov. 2017, [Peer-reviewed]
  English
• Trophic position and dietary breadth of bats revealed by nitrogen isotopic composition of amino acids
  Caitlin J. Campbell; David M. Nelson; Nanako O. Ogawa; Yoshito Chikaraishi; Naohiko Ohkouchi
  SCIENTIFIC REPORTS, 7, Nov. 2017, [Peer-reviewed]
  English, Scientific journal
• Fractionation of nitrogen isotopes during amino acid metabolism in heterotrophic and chemolithoautotrophic microbes across Eukarya, Bacteria, and Archaea: Effects of nitrogen sources and metabolic pathways
  Yasuhiko T. Yamaguchi; Yoshito Chikaraishi; Yoshinori Takano; Nanako O. Ogawa; Hiroyuki Imachi; Yusuke Yokoyama; Naohiko Ohkouchi
  ORGANIC GEOCHEMISTRY, 111, 101, 112, Sep. 2017, [Peer-reviewed]
  English, Scientific journal
• Comparing compound-specific and bulk stable nitrogen isotope trophic discrimination factors across multiple freshwater fish species and diets
  Chelsey M. Blanke; Yoshito Chikaraishi; Yuko Takizawa; Shawn A. Steffan; Prarthana S. Dharampal; M. Jake Vander Zanden
  CANADIAN JOURNAL OF FISHERIES AND AQUATIC SCIENCES, 74, 8, 1291, 1297, Aug. 2017, [Peer-reviewed]
  English, Scientific journal
• Trophic interaction among organisms in a seagrass meadow ecosystem as revealed by bulk δ13C and amino acid δ15N analyses
  Bohyung Choi; Sun-Yong Ha; Jae Seong Lee; Yoshito Chikaraishi; Naohiko Ohkouchi; Kyung-Hoon Shin
  Limnology and Oceanography, 62, 4, 1426, 1435, Wiley Blackwell, 01 Jul. 2017, [Peer-reviewed]
  English, Scientific journal
• Trophic interaction among organisms in a seagrass meadow ecosystem as revealed by bulk delta C-13 and amino acid delta N-15 analyses
  Bohyung Choi; Sun-Yong Ha; Jae Seong Lee; Yoshito Chikaraishi; Naohiko Ohkouchi; Kyung-Hoon Shin
  LIMNOLOGY AND OCEANOGRAPHY, 62, 4, 1426, 1435, Jul. 2017, [Peer-reviewed]
  English, Scientific journal
• Isotopic analyses suggest mammoth and plant in the diet of the oldest anatomically modern humans from far southeast Europe
  Dorothee G. Drucker; Yuichi I. Naito; Stephane Pean; Sandrine Prat; Laurent Crepin; Yoshito Chikaraishi; Naohiko Ohkouchi; Simon Puaud; Martina Laznickova-Galetova; Marylene Patou-Mathis; Aleksandr Yanevich; Herve Bocherens
  SCIENTIFIC REPORTS, 7, Jul. 2017, [Peer-reviewed]
  English, Scientific journal
• Preference for fish in a Neolithic hunter-gatherer community of the upper Tigris, elucidated by amino acid delta N-15 analysis
  Yu Itahashi; Yutaka Miyake; Osamu Maeda; Osamu Rondo; Hitomi Hongo; Wim Van Neer; Yoshito Chikaraishi; Naohiko Ohkouchi; Minoru Yoneda
  JOURNAL OF ARCHAEOLOGICAL SCIENCE, 82, 40, 49, Jun. 2017, [Peer-reviewed]
  English, Scientific journal
• Microbial Eukaryotes that Lack Sterols
  Takishita, Kiyotaka; Chikaraishi, Yoshito; Tanifuji, Goro; Ohkouchi, Naohiko; Hashimoto, Tetsuo; Fujikura, Katsunori; Roger, Andrew J
  The Journal of eukaryotic microbiology, 64, 6, 897, 900, WILEY, May 2017, [Peer-reviewed]
  English, Scientific journal, It is widely held that sterols are key cyclic triterpenoid lipids in eukaryotic cell membranes and are synthesized through oxygen-dependent multi-enzyme pathways. However, there are known exceptions-ciliated protozoans, such as Tetrahymena, along with diverse low-oxygen adapted eukaryotes produce, instead of sterols, the cyclic triterpenoid lipid tetrahymanol that does not require molecular oxygen for its biosynthesis. Here, we report that a number of anaerobic microbial eukaryotes (protists) utilize neither sterols nor tetrahymanol in their membranes. The lack of detectable sterol-like compounds in their membranes may provide an opportunity to reconsider the physiological function of sterols and sterol-like lipids in eukaryotes. This article is protected by copyright. All rights reserved.
• Intra-trophic isotopic discrimination of N-15/N-14 for amino acids in autotrophs: Implications for nitrogen dynamics in ecological studies
  Yuko Takizawa; Prarthana S. Dharampal; Shawn A. Steffan; Yoshinori Takano; Naohiko Ohkouchi; Yoshito Chikaraishi
  ECOLOGY AND EVOLUTION, 7, 9, 2916, 2924, May 2017, [Peer-reviewed]
  English, Scientific journal
• Genomic Evidence that Methanotrophic Endosymbionts Likely Provide Deep-Sea Bathymodiolus Mussels with a Sterol Intermediate in Cholesterol Biosynthesis
  Kiyotaka Takishita; Yoshihiro Takaki; Yoshito Chikaraishi; Tetsuro Ikuta; Genki Ozawa; Takao Yoshida; Naohiko Ohkouchi; Katsunori Fujikura
  GENOME BIOLOGY AND EVOLUTION, 9, 5, 1148, 1160, May 2017, [Peer-reviewed]
  English, Scientific journal
• Unpacking brown food-webs: Animal trophic identity reflects rampant microbivory
  Shawn A. Steffan; Yoshito Chikaraishi; Prarthana S. Dharampal; Jonathan N. Pauli; Christelle Guedot; Naohiko Ohkouchi
  ECOLOGY AND EVOLUTION, 7, 10, 3532, 3541, May 2017, [Peer-reviewed]
  English, Scientific journal
• Integrated trophic position decreases in more diverse communities of stream food webs
  Naoto F. Ishikawa; Yoshito Chikaraishi; Naohiko Ohkouchi; Aya R. Murakami; Ichiro Tayasu; Hiroyuki Togashi; Jun-ichi Okano; Yoichiro Sakai; Tomoya Iwata; Michio Kondoh; Noboru Okuda
  SCIENTIFIC REPORTS, 7, May 2017, [Peer-reviewed]
  English, Scientific journal
• Consistency in coral skeletal amino acid composition offshore of Palau in the western Pacific warm pool indicates no impact of decadal variability in nitricline depth on primary productivity
  Branwen Williams; Benoit Thibodeau; Yoshito Chikaraishi; Naohiko Ohkouchi; Andrew Walnum; Andréa G. Grottoli; Patrick L. Colin
  Limnology and Oceanography, 62, 2, 399, 407, Wiley Blackwell, 01 Mar. 2017, [Peer-reviewed]
  English, Scientific journal
• Trophic discrimination factor of nitrogen isotopes within amino acids in the dobsonfly Protohermes grandis (Megaloptera: Corydalidae) larvae in a controlled feeding experiment
  Naoto F. Ishikawa; Fumio Hayashi; Yoko Sasaki; Yoshito Chikaraishi; Naohiko Ohkouchi
  ECOLOGY AND EVOLUTION, 7, 6, 1674, 1679, Mar. 2017, [Peer-reviewed]
  English, Scientific journal
• Consistency in coral skeletal amino acid composition offshore of Palau in the western Pacific warm pool indicates no impact of decadal variability in nitricline depth on primary productivity
  Branwen Williams; Benoit Thibodeau; Yoshito Chikaraishi; Naohiko Ohkouchi; Andrew Walnum; Andrea G. Grottoli; Patrick L. Colin
  LIMNOLOGY AND OCEANOGRAPHY, 62, 2, 399, 407, Mar. 2017, [Peer-reviewed]
  English, Scientific journal
• Broad-scale trophic shift in the pelagic North Pacific revealed by an oceanic seabird
  Peggy H. Ostrom; Anne E. Wiley; Helen F. James; Sam Rossman; William A. Walker; Elise F. Zipkin; Yoshito Chikaraishi
  PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, 284, 1851, Mar. 2017, [Peer-reviewed]
  English, Scientific journal
• Nitrogen Isotopic Fractionation in Ammonia during Adsorption on Silicate Surfaces
  Haruna Sugahara; Yoshinori Takano; Nanako O. Ogawa; Yoshito Chikaraishi; Naohiko Ohkouchi
  ACS EARTH AND SPACE CHEMISTRY, 1, 1, 24, 29, Mar. 2017, [Peer-reviewed]
  English, Scientific journal
• A monitoring result of polychlorinated biphenyls (PCBs) in deep-sea organisms and sediments off Tohoku during 2012-2014: temporal variation and the relationship with the trophic position
  Ohkouchi Naohiko; Shibata H; Chikaraishi Y; Nomaki H; Ogawa N. O; Nagata T; Goto T; Fujikura K; Kitazato H
  JOURNAL OF OCEANOGRAPHY, 72, 4, 629, 639, Aug. 2016, [Peer-reviewed]
  English
• Evidence for herbivorous cave bears (Ursus spelaeus) in Goyet Cave, Belgium: implications for palaeodietary reconstruction of fossil bears using amino acid N-15 approaches
  Yuichi I. Naito; Mietje Germonpre; Yoshito Chikaraishi; Naohiko Ohkouchi; Dorothee G. Drucker; Keith A. Hobson; Mark A. Edwards; Christoph Wissing; Herve Bocherens
  JOURNAL OF QUATERNARY SCIENCE, 31, 6, 598, 606, Aug. 2016, [Peer-reviewed]
  English, Scientific journal
• Ecological niche of Neanderthals from Spy Cave revealed by nitrogen isotopes of individual amino acids in collagen
  Yuichi I. Naito; Yoshito Chikaraishi; Dorothee G. Drucker; Naohiko Ohkouchi; Patrick Semal; Christoph Wissing; Herve Bocherens
  JOURNAL OF HUMAN EVOLUTION, 93, 82, 90, Apr. 2016, [Peer-reviewed]
  English, Scientific journal
• Organic Reference Materials for Hydrogen, Carbon, and Nitrogen Stable Isotope-Ratio Measurements: Caffeines, n-Alkanes, Fatty Acid Methyl Esters, Glycines, L-Valines, Polyethylenes, and Oils
  Arndt Schimmelrnann; Haiping Qi; Tyler B. Coplen; Willi A. Brand; Jon Fong; Wolfram Meier-Augenstein; Helen F. Kemp; Blaza Toman; Annika Ackermann; Sergey Assonov; Anita T. Aerts-Bijma; Ramona Brejcha; Yoshito Chikaraishi; Tamim Darwish; Martin Elsner; Matthias Gehre; Heike Geilmann; Manfred Groeing; Jean-Francois Helie; Sara Herrero-Martin; Harro A. J. Meijer; Peter E. Sauer; Alex L. Sessions; Roland A. Werner
  ANALYTICAL CHEMISTRY, 88, 8, 4294, 4302, Apr. 2016, [Peer-reviewed]
  English, Scientific journal
• An overview of methods used for the detection of aquatic resource consumption by humans: Compound-specific delta N-15 analysis of amino acids in archaeological materials
  Yuichi I. Naito; Hervé Bocherens; Yoshito Chikaraishi; Dorothée G. Drucker; Christoph Wißing; Minoru Yoneda; Naohiko Ohkouchi
  Journal of Archaeological Science: Reports, 6, 720, 732, Apr. 2016, [Peer-reviewed]
  Scientific journal
• Debris by the huge Tsunami triggered by the Great East Japan Earthquake, Impact on the marine ecosystem
  Katsunori Fujikura; Yoshihiro Fujiwara; Yoshimi Takahashi; Naohiko Ohkouchi; Hiroshi Kitazato
  Nippon Suisan Gakkaishi (Japanese Edition), 82, 2, 136, Nihon Suisan Gakkai, 2016, [Peer-reviewed]
  Japanese, International conference proceedings
• アミノ酸（ピバロイル/ イソブチルエステル誘導体）のGC/MS による解析
  高野 淑識; 力石 嘉人; 大河内 直彦
  Researches in Organic Geochemistry, 32, 1, 1, 18, The Japanese Association of Organic Geochemists, 2016, [Peer-reviewed]
  Japanese,

  We report an analytical procedure of gas chromatography / mass spectrometry (GC / MS) focusing on chromatographic enantiomer separations and the corresponding mass spectra. We used N-pivaloyl isobutyl esters of amino acids to show the summary of retention time and those of mass fragmentation patters. To avoid matrix effect from biogeochemical samples, we optimized the entire experimental flow showing an optional wet chemical treatment for the purification of amino acids. We separated both of protein and non-protein type amino acids derived from the samples, including prokaryotic soft-tissues, freshwater / marine biological hard-tissues, and a deep-sea serpentine sample. Present derivatization procedures of amino acids as pivaloyl / isobutyl esters can be switchable on the diastereomers with the use of S-(+)-2-butyl esters or R-(-)-2-butyl esters. The present method will be applied into a further description of enantiomer-specific isotopic composition of individual amino acid.

• Organic matter transfer in Lake Superior's food web: Insights from bulk and molecular stable isotope and radiocarbon analyses.
  Kruger, B.R; Werne, J.P; Branstrator, D.K; Hrabik, T.R; Chikaraishi, Y; Ohkouchi, N; Minor, E.C
  Limnology and Oceanography, 61, 1, 149, 164, 2016, [Peer-reviewed]
• Amino acid compositions in heated carbonaceous chondrites and their compound-specific nitrogen isotopic ratios
  Queenie Hoi Shan Chan; Yoshito Chikaraishi; Yoshinori Takano; Nanako O. Ogawa; Naohiko Ohkouchi
  EARTH PLANETS AND SPACE, 68, Jan. 2016, [Peer-reviewed]
  English, Scientific journal
• Beneficial or not? Decoding carnivore roles in plant protection
  Shawn A. Steffan; Yoshito Chikaraishi; David R. Horton; Eugene Miliczky; Juan E. Zalapa; Vincent P. Jones; Naohiko Ohkouchi
  BIOLOGICAL CONTROL, 91, 34, 41, Dec. 2015, [Peer-reviewed]
  English, Scientific journal
• Microbes are trophic analogs of animals
  Shawn A. Steffan; Yoshito Chikaraishi; Cameron R. Currie; Heidi Horn; Hannah R. Gaines-Day; Jonathan N. Pauli; Juan E. Zalapa; Naohiko Ohkouchi
  PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 112, 49, 15119, 15124, Dec. 2015, [Peer-reviewed]
  English, Scientific journal
• Variation in the nitrogen isotopic composition of amino acids in benthic foraminifera: Implications for their adaptation to oxygen-depleted environments
  Hidetaka Nomaki; Yoshito Chikaraishi; Masashi Tsuchiya; Takashi Toyofuku; Hisami Suga; Yoko Sasaki; Katsuyuki Uematsu; Akihiro Tame; Naohiko Ohkouchi
  LIMNOLOGY AND OCEANOGRAPHY, 60, 6, 1906, 1916, Nov. 2015, [Peer-reviewed]
  English, Scientific journal
• Approach to determine individual trophic level and the difference in food sources of Japanese anchovy Engraulis japonicus in Sagami Bay, based on compound-specific nitrogen stable isotope analysis of amino acids
  Shunsaku Miyachi; Takeyuki Mayahara; Kouji Tsushima; Katsuhiro Sasada; Eiichi Kohno; Nanako O. Ogawa; Yoshito Chikaraishi; Naohiko Ohkouchi
  FISHERIES SCIENCE, 81, 6, 1053, 1062, Nov. 2015, [Peer-reviewed]
  English, Scientific journal
• Re-evaluation of nutrient sources for deep-sea wood-boring bivalves using the isotopic composition of bulk C, N, S, and amino acid nitrogen
  Toshiro Yamanaka; Sho Shimamura; Yoshito Chikaraishi; Takuma Haga; Yoshihiro Fujiwara
  MARINE ECOLOGY PROGRESS SERIES, 540, 157, 165, Nov. 2015, [Peer-reviewed]
  English, Scientific journal
• Uncovering the trophic relationship between Themisto gaudichaudii and Salpa thompsoni in the Antarctic Polar Frontal Zone
  Svenja Kruse; Evgeny A. Pakhomov; Brian P. V. Hunt; Yoshito Chikaraishi; Nanako O. Ogawa; Ulrich Bathmann
  MARINE ECOLOGY PROGRESS SERIES, 529, 63, 74, Jun. 2015, [Peer-reviewed]
  English, Scientific journal
• Diet quality influences isotopic discrimination among amino acids in an aquatic vertebrate
  Yoshito Chikaraishi; Shawn A. Steffan; Yoshinori Takano; Naohiko Ohkouchi
  ECOLOGY AND EVOLUTION, 5, 10, 2048, 2059, May 2015, [Peer-reviewed]
  English, Scientific journal
• Isolation of underivatized amino acids by ion-pair high performance liquid chromatography for precise measurement of nitrogen isotopic composition of amino acids: Development of comprehensive LC x GC/C/IRMS method
  Yoshinori Takano; Yoshito Chikaraishi; Naohiko Ohkouchi
  INTERNATIONAL JOURNAL OF MASS SPECTROMETRY, 379, 16, 25, Mar. 2015, [Peer-reviewed]
  English, Scientific journal
• Biochemical and physiological bases for the use of carbon and nitrogen isotopes in environmental and ecological studies
  Naohiko Ohkouchi; Nanako O. Ogawa; Yoshito Chikaraishi; Hiroyuki Tanaka; Eitaro Wada
  PROGRESS IN EARTH AND PLANETARY SCIENCE, 2, Feb. 2015, [Peer-reviewed]
  English
• Variation in the nitrogen isotopic composition of amino acids in benthic foraminifera: Implications for their adaptation to oxygen-depleted environments
  Hidetaka Nomaki; Yoshito Chikaraishi; Masashi Tsuchiya; Takashi Toyofuku; Hisami Suga; Yoko Sasaki; Katsuyuki Uematsu; Akihiro Tame; Naohiko Ohkouchi
  Limnology and Oceanography, 60, 6, 1906, 1916, Wiley Blackwell, 2015, [Peer-reviewed]
  English, Scientific journal
• 安定同位体分析による北西太平洋におけるカタクチイワシとマイワシの栄養段階と食源の推定.
  宮地 俊作; 馬谷原 武之; 對馬 孝治; 笹田 勝寛; 河野 英一; 川端 淳; 力石 嘉人; 小川 奈々子; 大河内 直彦
  日本生物地理学会会報, 70, 33, 41, 2015, [Peer-reviewed]
• イオンペアクロマトグラフィー／電子スプレーイオン化質量分析法 (LC/ESI-MS)によるアミノ酸のマススペクトル解析
  高野 淑識; 力石 嘉人; 大河内 直彦
  Researches in Organic Geochemistry, 31, 1, 33, 49, 2015, [Peer-reviewed]
• Are baby sprouts eating the proteins in the mother sweet potato?
  Takizawa Yuko; Chikaraishi Yoshito
  Researches in organic geochemistry, 30, 1, 29, 32, The Japanese Association of Organic Geochemists, Dec. 2014, [Peer-reviewed]
  English, Scientific journal, Sweet potatoes sometimes sprout the purple color of stems with several small leaves in the house pantry. In the present study, we investigated the trophic hierarchy between a mother sweet potato and its baby sprouts grown without any light in a dark house pantry, based on stable nitrogen isotopic composition (δ^<15>N,‰ vs. AIR) of glutamic acid and phenylalanine. The isotope data reveal that glutamic acid has a significant ^<15>N-enrichment (by 6.9‰) from the mother sweet potato to its baby sprout while phenylalanine has a little ^<15>5N-enrichment (by 0.6‰) between them. Interestingly, the isotopic heterogeneity found within the sweet potato is very similar to the isotopic discrimination generally found in the combination between plants and herbivores during grazing food webs (ca. 8.0‰ for glutamic acid and ca. 0.4‰ for phenylalanine). These results suggest that the proteins in the mother sweet potatoes are major resources for not only proteins in their baby sprouts but also growth energy in the sprouting, when they are grown heterotrophically without any light.
• Nitrate uptake by foraminifera and use in conjunction with endobionts under anoxic conditions
  Hidetaka Nomaki; Yoshito Chikaraishi; Masashi Tsuchiya; Takashi Toyofuku; Naohiko Ohkouchi; Katsuyuki Uematsu; Akihiro Tame; Hiroshi Kitazato
  LIMNOLOGY AND OCEANOGRAPHY, 59, 6, 1879, 1888, Nov. 2014, [Peer-reviewed]
  English, Scientific journal
• Influence of nitrogen substrates and substrate C:N ratios on the nitrogen isotopic composition of amino acids from the marine bacterium Vibrio harveyi
  K. Maki; N. Ohkouchi; Y. Chikaraishi; H. Fukuda; T. Miyajima; T. Nagata
  GEOCHIMICA ET COSMOCHIMICA ACTA, 140, 521, 530, Sep. 2014, [Peer-reviewed]
  English, Scientific journal
• High-resolution food webs based on nitrogen isotopic composition of amino acids
  Yoshito Chikaraishi; Shawn A. Steffan; Nanako O. Ogawa; Naoto F. Ishikawa; Yoko Sasaki; Masashi Tsuchiya; Naohiko Ohkouchi
  ECOLOGY AND EVOLUTION, 4, 12, 2423, 2449, Jun. 2014, [Peer-reviewed]
  English, Scientific journal
• New Amino Acid Reference Materials for Stable Nitrogen Isotope Analysis
  Rie Sato; Hidehiko Kawanishi; Arnd Schimmelmann; Yaeko Suzuki; Yoshito Chikaraishi
  BUNSEKI KAGAKU, 63, 5, 399, 403, May 2014, [Peer-reviewed]
  Japanese, Scientific journal
• Quantitative Analysis of Coenzyme F430 in Environmental Samples: A New Diagnostic Tool for Methanogenesis and Anaerobic Methane Oxidation
  Masanori Kaneko; Yoshinori Takano; Yoshito Chikaraishi; Nanako O. Ogawa; Susumu Asakawa; Takeshi Watanabe; Seigo Shima; Martin Krueger; Makoto Matsushita; Hiroyuki Kimura; Naohiko Ohkouchi
  ANALYTICAL CHEMISTRY, 86, 7, 3633, 3638, Apr. 2014, [Peer-reviewed]
  English, Scientific journal
• Stable Nitrogen Isotope Analysis of Amino Acids by Using Gas Chromatography/Isotope Ratio Mass Spectrometry (GC/IRMS) System with High-temperature Combustion Interface
  Kyoko Kamata; Yoshito Chikaraishi
  BUNSEKI KAGAKU, 63, 3, 279, 282, Mar. 2014, [Peer-reviewed]
  Japanese, Scientific journal
• Direct uptake of organic nitrogen by C4 plants: evidence from stable isotope analysis of amino acids
  Chikaraishi Yoshito; Takano Yoshinori; Ohkouchi Naohiko
  Abstracts of Annual Meeting of the Geochemical Society of Japan, 61, 23, 23, GEOCHEMICAL SOCIETY OF JAPAN, 2014
  Japanese, 本研究では，インゲン（C3植物）とトウモロコシ（C4植物）の苗の土壌に0.1mMの13C-15Nロイシン水溶液100mLを与え，苗葉中のアミノ酸の13C，15N濃度の変化を調べた。その結果，(1) C3植物では土壌アミノ酸の直接的な摂取が行われていないことを確認し，また一方で，(2) C4植物はC3植物とは異なり，土壌中のアミノ酸を直接取り込み，それを利用する能力があることがわかった。
• What modern people eat? Nitrogen isotopic composition of amino acids from nail
  Ohkouchi Naohiko; Chikaraishi Yoshito
  Abstracts of Annual Meeting of the Geochemical Society of Japan, 61, 24, 24, GEOCHEMICAL SOCIETY OF JAPAN, 2014
  Japanese, タンパク質を構成しているアミノ酸の窒素安定同位体比は，栄養段階の指標として用いることができる。現在，海棲生物，陸上C3植物系，陸上C4植物系の３種類の式が知られており，いずれの応用例もこれまでの生態学で得られた知見と非常によく一致する。本講演では，この方法論を現代人の爪に応用し，現代人の食性解析を行った結果を報告する。測定対象となったのは，日本人だけでなく欧州や南北アメリカ大陸の人々から採取さいた試料である。さらに日本人については，マーケットで売られている肉，野菜，魚などの多数の食品についても分析し，それらとの関係について考察する。
• Refinement of reconstructed ancient food webs based on the nitrogen isotopic compositions of amino acids from bone collagen: A case study of archaeological herbivores from Tell Ain el-Kerkh, Syria
  Yu Itahashi; Yoshito Chikaraishi; Naohiko Ohkouchi; Minoru Yoneda
  GEOCHEMICAL JOURNAL, 48, 6, E15, E19, 2014, [Peer-reviewed]
  English, Scientific journal
• 13C/12C Signatures in Plants and Algae
  Y. Chikaraishi
  Treatise on Geochemistry: Second Edition, 12, 95, 123, Elsevier Inc., Nov. 2013, [Peer-reviewed]
  English, In book
• Trophic position estimates of formalin-fixed samples with nitrogen isotopic compositions of amino acids: an application to gobiid fish (Isaza) in Lake Biwa, Japan
  Ogawa Nanako O; Chikaraishi Y; Ohkouchi N
  ECOLOGICAL RESEARCH, 28, 5, 697, 702, Sep. 2013, [Peer-reviewed]
  English
• Trophic Hierarchies Illuminated via Amino Acid Isotopic Analysis
  Shawn A. Steffan; Yoshito Chikaraishi; David R. Horton; Naohiko Ohkouchi; Merritt E. Singleton; Eugene Miliczky; David B. Hogg; Vincent P. Jones
  PLOS ONE, 8, 9, Sep. 2013, [Peer-reviewed]
  English, Scientific journal
• Nitrogen isotopic composition of collagen amino acids as an indicator of aquatic resource consumption: insights from Mesolithic and Epipalaeolithic archaeological sites in France
  Yuichi I. Naito; Yoshito Chikaraishi; Naohiko Ohkouchi; Dorothee G. Drucker; Herve Bocherens
  WORLD ARCHAEOLOGY, 45, 3, 338, 359, Aug. 2013, [Peer-reviewed]
  English, Scientific journal
• Evaluation of carnivory in inland Jomon hunter-gatherers based on nitrogen isotopic compositions of individual amino acids in bone collagen
  Yuichi I. Naito; Yoshito Chikaraishi; Naohiko Ohkouchi; Minoru Yoneda
  JOURNAL OF ARCHAEOLOGICAL SCIENCE, 40, 7, 2913, 2923, Jul. 2013, [Peer-reviewed]
  English, Scientific journal
• A preliminary estimate of the trophic position of the deep-water ram's horn squid Spirula spirula based on the nitrogen isotopic composition of amino acids
  Naohiko Ohkouchi; Ryuichi Tsuda; Yoshito Chikaraishi; Kazushige Tanabe
  MARINE BIOLOGY, 160, 4, 773, 779, Apr. 2013, [Peer-reviewed]
  English, Scientific journal
• Spatial distribution of sister species of vesicomyid bivalves Calyptogena okutanii and Calyptogena soyoae along an environmental gradient in chemosynthetic biological communities in Japan
  Hiromi Watanabe; Eriko Seo; Yoshimi Takahashi; Takao Yoshida; Shigeaki Kojima; Katsunori Fujikura; Hiroshi Miyake
  JOURNAL OF OCEANOGRAPHY, 69, 1, 129, 134, Feb. 2013, [Peer-reviewed]
  English, Scientific journal
• A low trophic position of Japanese eel larvae indicates feeding on marine snow
  Michael J. Miller; Yoshito Chikaraishi; Nanako O. Ogawa; Yoshiaki Yamada; Katsumi Tsukamoto; Naohiko Ohkouchi
  BIOLOGY LETTERS, 9, 1, Feb. 2013, [Peer-reviewed]
  English, Scientific journal
• Deuterium depletion in the fatty acids from beef
  Kanji Aoyagi; Akiko S. Goto; Tatsuya Fujino; Takashi Korenaga; Yoshito Chikaraishi
  Researches in Organic Geochemistry, 29, 65, 69, The Japanese Association of Organic Geochemists, 2013, [Peer-reviewed]
  English, We examined stable hydrogen (δD, ‰ relative to V-SMOW) and carbon isotopic compositions (δ^<13>C, ‰ relative to V-PDB) of fatty acids extracted from beef, and compared them with those from feeds (mixtures of plant materials) for the cattle. The δD value of stearic acid in beef is similar to that in the feeds, whereas the palmitic and oleic acids in beef are both significantly depleted in D (by ca. 60‰) as compared with the corresponding acids in the feeds. On the other hand, these fatty acids in beef are enriched in ^<13>C (by up to 5.7‰) relative to the corresponding acids in the feeds. Thus, the isotopic compositions of fatty acids in beef are not identical to those in the feeds. These results suggest that fatty acids in beef are an admixture of fatty acids derived from de novo biosynthesis in the cattle and from the feeds, and may imply that a considerable D-depletion process (e.g., hydrogenation of feed-derived fatty acids and/or dehydrogenation-hydrogenation cycling) occur in the fatty acids of the cattle.
• Reprint of "Stable hydrogen and carbon isotopic compositions of long-chain (C-21-C-33) n-alkanes and n-alkenes in insects"
  Yoshito Chikaraishi; Masanori Kaneko; Naohiko Ohkouchi
  GEOCHIMICA ET COSMOCHIMICA ACTA, 111, 78, 87, Jan. 2013, [Peer-reviewed]
  English, Scientific journal
• Stable hydrogen and carbon isotopic compositions of long-chain (C-21-C-33) n-alkanes and n-alkenes in insects
  Yoshito Chikaraishi; Masanori Kaneko; Naohiko Ohkouchi
  GEOCHIMICA ET COSMOCHIMICA ACTA, 95, 53, 62, Oct. 2012, [Peer-reviewed]
  English, Scientific journal
• Interlaboratory Comparison of Carbon, Nitrogen, and Oxygen Isotope Ratios in Organic Chemicals Using Elemental Analyzer-Isotope Ratio Mass Spectrometer
  Yaeko Suzuki; Yoshito Chikaraishi; Keita Yamada; Naohiro Yoshida
  BUNSEKI KAGAKU, 61, 9, 805, 810, Sep. 2012, [Peer-reviewed]
  Japanese, Scientific journal
• Algivore or Phototroph? Plakobranchus ocellatus (Gastropoda) Continuously Acquires Kleptoplasts and Nutrition from Multiple Algal Species in Nature
  Taro Maeda; Euichi Hirose; Yoshito Chikaraishi; Masaru Kawato; Kiyotaka Takishita; Takao Yoshida; Heroen Verbruggen; Jiro Tanaka; Shigeru Shimamura; Yoshihiro Takaki; Masashi Tsuchiya; Kenji Iwai; Tadashi Maruyama
  PLOS ONE, 7, 7, Jul. 2012, [Peer-reviewed]
  English, Scientific journal
• Diet Analysis Based on Nitrogen Isotopic Composition of Amino Acids
  OHKOUCHI Naohiko; CHIKARAISHI Yoshito; OGAWA Nanako O
  KAGAKU TO SEIBUTSU, 50, 6, 430, 434, Japan Society for Bioscience, Biotechnology, and Agrochemistry, 01 Jun. 2012
  Japanese, 生体中に含まれるアミノ酸の窒素安定同位体比を精密に測定することによって，自然界に暮らす生き物の栄養段階を推定する方法が開発された．この手法を用いれば，各種生態系の解析に役立つだけでなく，環境変化が生物の食性に及ぼしてきた影響や，過去の人類の食性など，さまざまな応用研究が可能になる．
• Lateral transfer of tetrahymanol-synthesizing genes has allowed multiple diverse eukaryote lineages to independently adapt to environments without oxygen
  Kiyotaka Takishita; Yoshito Chikaraishi; Michelle M. Leger; Eunsoo Kim; Akinori Yabuki; Naohiko Ohkouchi; Andrew J. Roger
  BIOLOGY DIRECT, 7, Feb. 2012, [Peer-reviewed]
  English, Scientific journal
• Methyl and ethyl chloroformate derivatizations for compound-specific stable isotope analysis of fatty acids-II
  Aoyagi Kanji; Yamanaka Atsuko; Goto Akiko S.; Fujino Tatsuya; Korenaga Takashi; Chikaraishi Yoshito
  Researches in Organic Geochemistry, 28, 27, 30, The Japanese Association of Organic Geochemists, 2012, [Peer-reviewed]
  English, Methyl (MCF) and ethyl chloroformate (ECF) derivatizations are potentially useful for rapid and simple esterification (i.e., at room temperature for 5 min) prior to compound-specific stable isotope analysis (CSIA) of fatty acids. In this study, we have used acetonitrile as an organic solvent in the esterification process to improve the yields of derivatives, and we evaluated whether the improved esterification is suitable for carbon and hydrogen CSIA. Six saturated (14:0, 16:0, 18:0, 20:0, 22:0, and 24:0) and three unsaturated (18:1 n-9, 18:2 n-6, and 18:3 n-3) fatty acids were used in this study. The yields of derivatives are 67-107% for MCF and 84-89% for ECF derivatizations, which are approximately twice the yields obtained in MCF and ECF derivatizations that did not use acetonitrile. The accuracy of the CSIA is <±0.4‰ (1σ) for carbon and <± 11‰ (1σ) for hydrogen, with no significant differences in these uncertainties observed for saturated and unsaturated fatty acids. Thus, MCF and ECF derivatizations using acetonitrile are suitable for the CSIA of fatty acids.
• Ecosystem study of Lake Baikal from nitrogen isotopic analysis of amino acids
  Ogawa Nanako; Chikaraishi Yoshito; Wada Eitaro; Ohkouchi Naohiko
  Abstracts of Annual Meeting of the Geochemical Society of Japan, 59, 186, GEOCHEMICAL SOCIETY OF JAPAN, 2012
  Japanese, アミノ酸窒素同位体比による生態系解析手法では、生物による窒素代謝におけるフェニルアラニンとグルタミン酸の窒素安定同位体比の挙動の差から各生物の栄養段階を推定する。本研究ではシベリアに位置する巨大な古代湖であり、数多くの固有種が存在するバイカル湖沖帯生態系生物について、アミノ酸窒素安定同位体比による食物網解析手法を応用し、アミノ酸窒素安定同位体比分布と生態系構造についての解析した。各沖帯生物の栄養段階は、一次生産者の珪藻が1.0、動物プランクトンのコペポーダが2.0、端脚類が2.2を示し、これらを捕食するコレゴヌス科の魚は3.3~3.8を示した。魚食魚の浮遊性カジカ類は4.2～4.4であった。バイカルアザラシは5.0となり最高次の捕食者であることが示された。個々のアミノ酸窒素安定同位体比分布からは、湖内の環境変動が大きいことも推察され、本手法の環境動態変動に対する解析ツールとしての有用性が示唆された。
• Ecology of deep-sea benthic archaea: insight from intra-molecular isotope signatures for salvage and de novo pathway
  TAKANO Yoshinori; CHIKARAISHI Yoshito; OHKOUCHI Naohiko
  Chikyukagaku, 46, 2, 113, 128, The Geochemical Society of Japan, 2012
  Japanese, Since the first classification by Woese and Fox (1977), Archaea, one of three domains of life, had been originally believed to exist in extreme environments including high temperature, high salinity, low oxygen concentration. However, recent advances in molecular and phylogenic approaches revealed their widespread distribution in marine and terrestrial environment including deep subsurface biosphere. The planktonic and benthic archaeal assemblages include two major phyla Euryarchaeota and Crenarchaeota. The novel phylum have been also proposed recently as Thaumarchaota, Korarchaota, and Nanoarchaeota. To elucidate unknown archaeal ecology, we evaluated intra-molecular isotopic composition to focus into archaeal membrane lipid biosynthesis using ¹³C-tracing techniques. The novel molecular diagnosis showed heterogenous ¹³C-incorporation driven by salvage (recycling) and de novo pathways in energy-limited environment such as deep-sea environments. Here, we reviewed the recent knowledge of prokaryotic ecology and biogeochemistry from intra-molecular isotopic signatures.
• Does the symbiotic scale-worm feed on the host mussel in deep-sea vent fields? Researches in Organic Geochemistry
  Takahashi, Y; Y. Sasaki; Y. Chikaraishi; M. Tsuchiya; H. Watanabe; T. Asahida; T. Maruyama; K. Fujikura
  Researches in Organic Geochemistry, 28, 23, 26, The Japanese Association of Organic Geochemists, 2012, [Peer-reviewed]
  English, Scientific journal, The scale-worm Branchipolynoe pettiboneae is frequently found in the mantle cavity of Bathymodiolus mussels living in hydrothermal vents and seeps around Japan. To investigate its feeding habits and symbiotic relationship with the host mussels, we determined the stable nitrogen isotopic composition of glutamic acid and phenylalanine for representative scale-worms including a symbiotic juvenile and a symbiotic adult, both with their host mussels, and a free-living adult, collected from hydrothermal vents of the Hatoma Knoll (〜1532 m in depth) in the Okinawa Trough, Japan. The isotopic data suggested the feeding habits that Bathymodiolus platifrons is a major source of amino acids for symbiotic adult scale-worm but not for free-living adult and symbiotic juvenile scale-worms.
• Molecular Paleohydrology: Interpreting the Hydrogen- Isotopic Composition of Lipid Biomarkers from Photosynthesizing Organisms
  Dirk Sachse; Isabelle Billault; Gabriel J. Bowen; Yoshito Chikaraishi; Todd E. Dawson; Sarah J. Feakins; Katherine H. Freeman; Clayton R. Magill; Francesca A. McInerney; Marcel T. J. van der Meer; Pratigya Polissar; Richard J. Robins; Julian P. Sachs; Hanns-Ludwig Schmidt; Alex L. Sessions; James W. C. White; Jason B. West; Ansgar Kahmen
  ANNUAL REVIEW OF EARTH AND PLANETARY SCIENCES, VOL 40, 40, 221, 249, 2012, [Peer-reviewed]
  English, In book
• Mammalian DNA delta N-15 exhibits 40 parts per thousand intramolecular variation and is unresponsive to dietary protein level
  Maggie S. Strable; Carolyn L. Tschanz; Behzad Varamini; Yoshito Chikaraishi; Naohiko Ohkouchi; J. Thomas Brenna
  RAPID COMMUNICATIONS IN MASS SPECTROMETRY, 25, 23, 3555, 3562, Dec. 2011, [Peer-reviewed]
  English, Scientific journal
• Food chain analysis by nitrogen isotopic composition of amino acids : Application to terrestrial environments(Advances in molecular and stable isotope studies among the organic geochemical and related communities (Part II))
  Chikaraishi Yoshito; Takano Yoshinori; Ogawa Nanako O; Sasaki Yoko; Tsuchiya Masashi; Ohkouchi Naohiko
  Researches in organic geochemistry, 27, 3, 11, The Japanese Association of Organic Geochemists, 30 Sep. 2011
  Japanese, Recent evidences have suggested that compound-specific stable isotope analysis (CSIA) of amino acids has been employed as a new powerful method with that enables the estimation of trophic level of organisms in not only aquatic but also terrestrial food webs. This CSIA approach is based on contrasting the ^<15>N-enrichment with each trophic level between two common amino acids: glutamic acid shows significant enrichment of +8.0‰ with each trophic level, whereas phenylalanine shows little enrichment of +0.4‰. These ^<15>N-enrichments are well consistent in both aquatic and terrestrial organis...
• N-15/N-14 ratios of amino acids as a tool for studying terrestrial food webs: a case study of terrestrial insects (bees, wasps, and hornets)
  Yoshito Chikaraishi; Nanako O. Ogawa; Hideyuki Doi; Naohiko Ohkouchi
  ECOLOGICAL RESEARCH, 26, 4, 835, 844, Jul. 2011, [Peer-reviewed]
  English, Scientific journal
• マイワシとカタクチイワシの栄養段階と食源:全窒素・炭素及びアミノ酸窒素の安定同位体比を用いた食性解析
  宮地俊作; 馬谷原武之; 對馬孝治; 笹田勝寛; 河野英一; 伊藤絹子; 川端淳; 力石嘉人; 小川奈々子; 大河内直彦
  日本水産学会大会講演要旨集, 2011, 77, 27 Mar. 2011
  Japanese
• Temperature effect on leaf water deuterium enrichment and isotopic fractionation during leaf lipid biosynthesis: Results from controlled growth of C-3 and C-4 land plants
  Youping Zhou; Kliti Grice; Yoshito Chikaraishi; Hilary Stuart-Williams; Graham D. Farquhar; Naohiko Ohkouchi
  PHYTOCHEMISTRY, 72, 2-3, 207, 213, Feb. 2011, [Peer-reviewed]
  English, Scientific journal
• Compound-specific nitrogen isotope compositions of amino acid as a tool for food-web analysis
  Ogawa Nanako O.; Chikaraishi Yoshito; Wada Eitaro; Ohkouchi Naohiko
  Abstracts of Annual Meeting of the Geochemical Society of Japan, 58, 91, 91, GEOCHEMICAL SOCIETY OF JAPAN, 2011
  生物を構成する有機物の安定同位体比は、生態系における一次生産者の光合成メカニズムや基質、食物連鎖の構造や変化などを解析する上で、優れた指標である。生物を構成するアミノ酸では、捕食による窒素代謝の過程で、アミノ酸の種類により15N濃縮の大きさに差が生じることが明らかとなってきた。この結果はほとんどの水界生態系・陸上生態系生物に共通しており、こうしたアミノ酸窒素安定同位体比の比較から、生態系生物の栄養段階の算出も可能となる。本講演ではバイカル湖での結果を中心に、私たちの研究グループにおけるアミノ酸の分子レベル窒素安定同位体比を用いた生態系生物に関する研究について紹介する。
• Dietary reconstruction of prehistoric human populations in Japan using nitrogen isotopic analysis of individual amino acids in bone
  Naito Yuichi; Honch Noah; Chikaraishi Yoshito; Ohkouchi Naohiko; Yoneda Minoru
  Abstracts of Annual Meeting of the Geochemical Society of Japan, 58, 0, 151, 151, GEOCHEMICAL SOCIETY OF JAPAN, 2011, [Peer-reviewed]
  We investigated the stable nitrogen isotopic compositions of individual amino acids from human and faunal remains from a variety of archaeological sites in Japan in order to reconstruct the prehistoric human diets. In this study characteristic isotopic compositions were observed among the human populations in different regions and different periods, which were most clearly reflected in the nitrogen isotopic values of glutamic acid (+23 to +32⁰/₀₀ for the coastal regions and +10 to +12⁰/₀₀ for the inland regions) and phenylalanine (0 to +7⁰/₀₀ for the coastal regions and +6 to +7⁰/₀₀ for the inland regions) in bones. It should be noted that the nitrogen isotopic composition of these amino acids could be useful to quantitatively evaluate dietary contribution to the human diets from marine, freshwater and terrestrial ecosystems. For example, by applying the new method to above samples, we estimated that the coastal Jomon populations would obtain >70% of their dietary protein from marine resources. In contrast, it seems that inland Jomon and the Paleolithic populations exploited little protein from marine and freshwater resources.
• Methyl and ethyl chloroformate derivatizations for compound-specific stable isotope analysis (CSIA) of fatty acids
  Akiko S. Goto; Takashi Korenaga; Yoshito Chikaraishi
  Researches in Organic Geochemistry, 27, 91, 95, 2011, [Peer-reviewed]
• Dietary adaptations of prehistoric Japanese in light of nitrogen isotopic compositions of bone collagen amino acids: with special focus on aquatic resources
  Yuichi I. Naito; Noah V. Honch; Yoshito Chikaraishi; Naohiko Ohkouchi; Minoru Yoneda
  AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, 144, 223, 223, 2011, [Peer-reviewed]
  English
• Evaluation of algal contribution to aquatic insects based on ¹³C/¹²C and C/N ratios
  Fumikazu Akamatsu; Masamichi Yamamoto; Yoshito Chikaraishi; Hideshige Toda
  Researches in Organic Geochemistry, 26, 107, 114, 日本有機地球化学会, Dec. 2010, [Peer-reviewed]
• Sedimentary membrane lipids recycled by deep-sea benthic archaea
  Yoshinori Takano; Yoshito Chikaraishi; Nanako O. Ogawa; Hidetaka Nomaki; Yuki Morono; Fumio Inagaki; Hiroshi Kitazato; Kai-Uwe Hinrichs; Naohiko Ohkouchi
  NATURE GEOSCIENCE, 3, 12, 858, 861, Dec. 2010, [Peer-reviewed]
  English, Scientific journal
• Quantitative Evaluation of Marine Protein Contribution in Ancient Diets Based on Nitrogen Isotope Ratios of Individual Amino Acids in Bone Collagen: An Investigation at the Kitakogane Jomon Site
  Yuichi I. Naito; Noah V. Honch; Yoshito Chikaraishi; Naohiko Ohkouchi; Minoru Yoneda
  AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, 143, 1, 31, 40, Sep. 2010, [Peer-reviewed]
  English, Scientific journal
• Isolation and desalting with cation-exchange chromatography for compound-specific nitrogen isotope analysis of amino acids: application to biogeochemical samples
  Yoshinori Takano; Yuichiro Kashiyama; Nanako O. Ogawa; Yoshito Chikaraishi; Naohiko Ohkouchi
  RAPID COMMUNICATIONS IN MASS SPECTROMETRY, 24, 16, 2317, 2323, Aug. 2010, [Peer-reviewed]
  English, Scientific journal
• GC/MS analysis of polyunsaturated fatty acids: Rapid separation and structural assignment with polar GC column
  Naito, Y. I; Yamaguchi Y. T; Chikaraishi Y; Ohkouchi N
  Researches in Organic Geochemistry, 26, 139, 145, The Japanese Association of Organic Geochemists, 2010, [Peer-reviewed]
  Japanese, Scientific journal
• DIETARY RECONSTRUCTION OF THE OKHOTSK CULTURE OF HOKKAIDO, JAPAN, BASED ON NITROGEN COMPOSITION OF AMINO ACIDS: IMPLICATIONS FOR CORRECTION OF C-14 MARINE RESERVOIR EFFECTS ON HUMAN BONES
  Yuichi I. Naito; Yoshito Chikaraishi; Naohiko Ohkouchi; Hitoshi Mukai; Yasuyuki Shibata; Noah V. Honch; Yukio Dodo; Hajime Ishida; Tetsuya Amano; Hiroko Ono; Minoru Yoneda
  RADIOCARBON, 52, 2, 671, 681, 2010, [Peer-reviewed]
  English, Scientific journal
• Determination of aquatic food-web structure based on compound-specific nitrogen isotopic composition of amino acids
  Yoshito Chikaraishi; Nanako O. Ogawa; Yuichiro Kashiyama; Yoshinori Takano; Hisami Suga; Akiko Tomitani; Hideaki Miyashita; Hiroshi Kitazato; Naohiko Ohkouchi
  LIMNOLOGY AND OCEANOGRAPHY-METHODS, 7, 740, 750, Nov. 2009, [Peer-reviewed]
  English, Scientific journal
• Degradation of algal lipids by deep-sea benthic foraminifera: An in situ tracer experiment
  Hidetaka Nomaki; Naohiko Ohkouchi; Petra Heinz; Hisami Suga; Yoshito Chikaraishi; Nanako O. Ogawa; Kouhei Matsumoto; Hiroshi Kitazato
  DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS, 56, 9, 1488, 1503, Sep. 2009, [Peer-reviewed]
  English, Scientific journal
• Fractionation of hydrogen isotopes during phytol biosynthesis
  Yoshito Chikaraishi; Ryouichi Tanaka; Ayumi Tanaka; Naohiko Ohkouchi
  ORGANIC GEOCHEMISTRY, 40, 5, 569, 573, May 2009, [Peer-reviewed]
  English, Scientific journal
• Development of biogeochemical proxies based on physiological knowledge
  Chikaraishi Yoshito
  Abstracts of Annual Meeting of the Geochemical Society of Japan, 56, 155, 155, GEOCHEMICAL SOCIETY OF JAPAN, 2009
  これまで，有機化合物やその安定同位体比を用いた様々な指標が提案され，地球化学の様々な課題に対して多くの知見を提供している。近年，生理学的な基本原理をよく理解して，そのしくみを利用した新規指標の開発（または，従来の指標の大幅な改善）が行われるようになりつつある。生物は，体内の生理活性を非常に上手くコントロールし，その調整には様々な特性の有機化合物が密接に関係している。また生物による有機化合物の生合成・代謝は，ほとんどの場合，安定同位体組成の変化を伴い，その大きさは反応の進み具合と密接な関係を持つ。すなわち，我々が知りたい生物地球化学的情報にダイレクトに関わる生理活性を見出し，それに関係する有機化合物，または安定同位体比の変化を環境試料から明確にとらえることができれば，それが優れた指標となる可能性が高い。発表では、生理学的な知見を利用する新指標のアイデア・基本原理とその実例を紹介する。
• テトラピロール化合物の炭素アイソトポマーと基礎生産者の炭酸同化プロセス
  柏山 祐一郎; 力石 嘉人; 小川 奈々子; 大河内 直彦
  日本地球化学会年会要旨集, 56, 152, 152, 日本地球化学会, 2009
  Japanese, クロロフィルのテトラピロール骨格のメチン架橋位の炭素同位体組成を，分子全体と酸化分解により得られるマレイミド類の炭素同位体組成を比較することで求められる．本講演では，高等植物とシアノバクテリアから得られたクロロフィルａの値をもとに，後者のチン架橋位の炭素同位体組成がβカルボキシレーションによる重炭酸の同化を反映して，実際に大きな値をとるかどうかを検証する．また，東北日本の中新統女川層から得られた化石ポルフィリン（のメチン架橋位の炭素同位体組成を求め，当時の基礎生産におけるシアノバクテリアの寄与について議論する．
• GC/MS analysis of amino acids as ethoxycarbonyl ethyl ester
  Yamaguchi, Y. T; Chikaraishi Y; Yokoyama Y; Ohkouchi N
  Researches in Organic Geochemistry, 25, 71, 83, 2009, [Peer-reviewed]
  Japanese, Scientific journal
• Compound-Specific Nitrogen Isotope Analysis of D-Alanine, L-Alanine, and Valine: Application of Diastereomer Separation to delta N-15 and Microbial Peptidoglycan Studies
  Yoshinori Takano; Yoshito Chikaraishi; Nanako O. Ogawa; Hiroshi Kitazato; Naohiko Ohkouchi
  ANALYTICAL CHEMISTRY, 81, 1, 394, 399, Jan. 2009, [Peer-reviewed]
  English, Scientific journal
• Evidence of global chlorophyll d
  Y. Kashiyama; H. Miyashita; S. Ohkubo; N.O. Ogawa; Y. Chikaraishi; Y. Takano; H. Suga; T. Toyofuku; H. Nomaki; H. Kitazato; T. Nagata; N. Ohkouchi
  Science, 321, 5889, 658, 658, 01 Aug. 2008, [Peer-reviewed]
  English
• Geographical origin of polished rice based on multiple element and stable isotope analyses
  Yaeko Suzuki; Yoshito Chikaraishi; Nanako O. Ogawa; Naohiko Ohkouchi; Takashi Korenaga
  FOOD CHEMISTRY, 109, 2, 470, 475, Jul. 2008, [Peer-reviewed]
  English, Scientific journal
• Stable carbon, nitrogen, and oxygen isotope analysis as a potential tool for verifying geographical origin of beef
  Rumiko Nakashita; Yaeko Suzuki; Fumikazu Akamatsu; Yoshiko Iizumi; Takashi Korenaga; Yoshito Chikaraishi
  ANALYTICA CHIMICA ACTA, 617, 1-2, 148, 152, Jun. 2008, [Peer-reviewed]
  English, Scientific journal
• Microbially induced formation of ooid-like coated grains in the Late Cretaceous methane-seep deposits of the Nakagawa area, Hokkaido, northern Japan
  Robert Gwyn Jenkins; Yoshinori Hikida; Yoshito Chikaraishi; Naohiko Ohkouchi; Kazushige Tanabe
  ISLAND ARC, 17, 2, 261, 269, Jun. 2008, [Peer-reviewed]
  English, Scientific journal
• In-situ tracer experiments for benthic Archaea: carbon isotopic evidence of metabolic activity from archaeal membrane lipids
  Takano Yoshinori; Nomaki Hidetaka; Ogawa Nanako; Chikaraishi Yoshito; Inagaki Fumio; Kitazato Hiroshi; Ohkouchi Naohiko
  Abstracts of Annual Meeting of the Geochemical Society of Japan, 55, 154, 154, GEOCHEMICAL SOCIETY OF JAPAN, 2008
  原核生物の古細菌や真正細菌には、特有のバイオマーカーが存在する。例えば古細菌は、カルドアーキオール(Caldarchaeol)やクレンアーキオール(Crenarchaeol)に代表される極性脂質化合物を保有する。それらの分子は、微生物の成育・増殖とともに新たに産生されるため、同位体トレーサー基質を取り込んだ場合、その代謝のシグナルは、微生物細胞やそれを構成するバイオマーカー分子に反映される。堆積物から古細菌の細胞のみを単離するのは困難なため、古細菌を構成するバイオマーカー分子を分離・解析することで炭素源の取込みや代謝の活性を評価できる(eg. Pearson et al., 2001)。まず、海底堆積物中での微生物活性を測る目的で、古細菌に由来するバイオマーカーを単離・精製し、分子レベル安定炭素同位体比を評価する分析ラインを確立した。次に、海底表層と堆積物浅層で同位体ラベルを使ったトレーサー実験試料を用いて、海底堆積物に棲む古細菌の代謝活性の有無を調べた。海底堆積物浅層に棲息する古細菌は、1) 埋没後も脂質の生合成が行われ代謝活性があること、2)迫{9日間という時間スケールであっても代謝活性のシグナルが観測されることを示した。
• Stable isotope abundances in cyanobacterial phycobiliproteins
  Ogawa Nanako O.; Chikaraishi Yoshito; Kashiyama Yuichiro; Tomitani Akiko; Kitazato Hiroshi; Ohkouchi Naohiko
  Abstracts of Annual Meeting of the Geochemical Society of Japan, 55, 184, 184, GEOCHEMICAL SOCIETY OF JAPAN, 2008
  光合成生物は、光(エネルギー)の吸収(捕集)のために、光合成色素とよばれる有色の化合物を用いている。それらは大きくクロロフィル、カロテノイド、フィコビリンの三つに分類される。このうちクロロフィルとカロチノイドは高等植物や多くの藻類に存在するが、フィコビリンはシアノバクテリアや、紅藻などの藻類の一部がもつ色素である。シアノバクテリアは、これまでのクロロフィル系の色素化合物とその関連有機化合物の安定同位体比研究から、先カンブリア代や海洋無酸素事変時の地球環境の変動に大きく関与していることが示唆されてきた。一方、フィコビリンはシアノバクテリアがもつ光合成色素であり、シアノバクテリアのバイオマーカーとして各種情報を保持している可能性が推察されるものの、蛋白質と結合しているため従来の実験手法では分離測定が困難であった。したがって、これまで地球化学的な知見をあまり多く得ることができていない。本研究では、１）フィコビリンの分析法の確立と、２）それが記録する地球生物学的な情報を知るために、迫{シアノバクテリア試料中に含まれる「フィコビリン蛋白質（phycobiliproteins, PBP）」を分離し、その安定同位体比を測定した。実験には室温で迫{された各種のシアノバクテリアを用いた。リン酸バッファーを用いて抽出したPBPは、逆相HPLCにより分離した(図１)。各PBPはピーク毎にフラクションコレクターによって捕集し、安定同位体比等の分析を行った。本講演では、その結果について報告する。
• Compound-specific nitrogen isotope composition for stereoisomers: D- and L-alanine in peptidoglycan from prokaryote
  Takano Yoshinori; Chikaraishi Yoshito; Ogawa Nanako; Kitazato Hiroshi; Ohkouchi Naohiko
  Abstracts of Annual Meeting of the Geochemical Society of Japan, 55, 189, 189, GEOCHEMICAL SOCIETY OF JAPAN, 2008
  原核生物のうち真正細菌の細胞壁には、主としてその強度と形態を支えるために堅い層が存在する。特にグラム陽性の細胞壁は、その約90%がペプチドグリカン（数層～約25層）から構成され、凖難分解性の性質を持つ。細胞内のタンパク質を構成するアミノ酸は、基本的にL-体であるが、細胞壁のペプチドグリカンには、２つの糖誘導体であるN-アセチルグルコサミンとN-アセチルムラミン酸にD-アラニンやD-グルタミン酸などのD-アミノ酸を含むペプチドが架橋している。ペプチドグリカン由来のD-アラニンは、真正細菌のバイオマーカーの一つと考えられている。ここでは、まず様々な地球化学試料に含まれる立体異性体分子レベル窒素同位体比を得るための分析法を確立した。次に、応用の一つとして原核生物の細胞組織であるペプチドグリカン、シュードペプチドグリカン由来のD-, L-アラニンについて評価し、立体異性体分子レベルで特徴的な同位体比の分配が見られたので報告する。
• Nitrogen isotope analysis of amino acids as a tool for elucidating food web
  Chikaraishi Yoshito
  Abstracts of Annual Meeting of the Geochemical Society of Japan, 55, 187, 187, GEOCHEMICAL SOCIETY OF JAPAN, 2008
  生体試料のバルクの窒素安定同位体比は、食物連鎖網の解析や栄養段階の推定などの生態学研究において、ほとんど必須のツールとして広く用いられている。しかし、食物連鎖に伴う窒素同位体比の上昇が生物ごとに大きく変動することや、一次生産者の妥当な同位体比を得ることが難しいことから、見積もられる栄養段階の誤差が常に議論の対象になってきた。ところが近年、生物に含まれるアミノ酸には、食物連鎖に伴い15Nが濃縮するものと、食物連鎖の影響を受けずに同位体比が変化しないものが存在し、両者の同位体比を比較することで、その生物の栄養段階や、食物連鎖網のベースにある生物の同位体比を精度良く見積もることができることがわかってきた。発表では、アミノ酸の窒素同位体比分析法の概要と、これまでに我々の研究室で得られた結果を紹介する。
• Dietary reconstruction of Jomon human remains in Hokkaido utilizing nitrogen isotopic analysis of amino acids
  Naito Yuichi
  Abstracts of Annual Meeting of the Geochemical Society of Japan, 55, 0, 188, 188, GEOCHEMICAL SOCIETY OF JAPAN, 2008, [Peer-reviewed]
  It has been shown that the compound-specific amino acid analysis of nitrogen isotopic values in biological samples is quite useful for reconstructing food-web structures in aquatic ecosystems. However, very little research has been applied to archaeological and terrestrial ecosystems because there is not yet enough knowledge regarding terrestrial ecological settings. On the other hand, the biological proteins in excavated bones are generally stable over long periods with respect to their chemical structure so that application to paleoecosystems using amino acid analysis may be possible. In this study, we apply this method to human and animal remains of deer, fur seal and oyster in order to evaluate the validity of the method. We sampled human bone recovered from the Kitakogane site from the late Jomon period (ca. 5200-5700 BP) in Hokkaido Japan who relied on terrestrial and marine mammals for their subsistence. Moreover, we evaluated the dietary habits of humans quantitatively by measuring the nitrogen isotopic values of specific amino acids.
• Compound-specific isotope analysis (CSIA) by gas chromatography/isotope ratio mass spectrometer (GC/IRMS)
  CHIKARAISHI Yoshito; OBA Yasuhiro
  Researches in organic geochemistry, 23/24, 99, 122, The Japanese Association of Organic Geochemists, 2008, [Peer-reviewed]
  Japanese, Scientific journal, One of the most powerful techniques in the molecular isotope studies is compound-specific isotope analysis (CSIA) by gas chromatograph/isotope ratio mass spectrometer (GC/IRMS), which allows a rapid and precise determination of stable carbon, nitrogen, and hydrogen (and oxygen) isotopic compositions of individual compounds even in complex mixture of components. After commercial production of GC/IRMS in the 1990s, CSIA has explosively been used for many fields of studies, particularly among the organic geochemical community as a powerful tool for tracing sources and delivery of organic compounds in geological and geographical samples and for reconstructing paleoenvironments. However, it is also true that fundamental analytical parameters of GC/IRMS has not been known extensively, which often leads to unreliable determination of the isotopic compositions. Unfortunately, based on such unreliable determination, several studies have unconsciously reported essentially inaccurate data and associated discussion. Therefore, in this paper, we review a brief outline of GC/IRMS and associated methodologies, and summarize the instrumental factors influencing accuracy and precision of the isotope measurements. We hope that this paper is useful for applying CSIA to future studies.
• A compound-specific isotope method for measuring the stable nitrogen isotopic composition of tetrapyrroles
  Yoshito Chikaraishi; Yuichiro Kashiyama; Nanako O. Ogawa; Hiroshi Kitazato; Mitsuru Satoh; Shinya Nomoto; Naohiko Ohkouchi
  ORGANIC GEOCHEMISTRY, 39, 5, 510, 520, 2008, [Peer-reviewed]
  English, Scientific journal
• Carbon isotopic composition of the tetrapyrrole nucleus in chloropigments from a saline meromictic lake: A mechanistic view for interpreting the isotopic signature of alkyl porphyrins in geological samples
  Naohiko Ohkouchi; Yoji Nakajima; Nanako O. Ogawa; Yoshito Chikaraishi; Hisami Suga; Saburo Sakai; Hiroshi Kitazato
  ORGANIC GEOCHEMISTRY, 39, 5, 521, 531, 2008, [Peer-reviewed]
  English, Scientific journal
• Application of compound-specific radiocarbon dating for studying west antarctic ice sheet during the late quaternary
  N. Ohkouhi; T. I. Eglinton; M. Toyoda; Y. Chikaraishi; H. Tokuyama; H. Miura; Y. Yokoyama
  GEOCHIMICA ET COSMOCHIMICA ACTA, 71, 15, A732, A732, Aug. 2007, [Peer-reviewed]
  English
• delta C-13 and delta D relationships among three n-alkyl compound classes (n-alkanoic acid, n-alkane and n-alkanol) of terrestrial higher plants
  Yoshito Chikaraishi; Hiroshi Naraoka
  ORGANIC GEOCHEMISTRY, 38, 2, 198, 215, 2007, [Peer-reviewed]
  English, Scientific journal
• Sources and transformation processes of pheopigments: Stable carbon and hydrogen isotopic evidence from Lake Haruna, Japan
  Yoshito Chikaraishi; Kohei Matsumoto; Hiroshi Kitazato; Naohiko Ohkouchi
  ORGANIC GEOCHEMISTRY, 38, 6, 985, 1001, 2007, [Peer-reviewed]
  English, Scientific journal
• Metabolic control of nitrogen isotope composition of amino acids in macroalgae and gastropods: implications for aquatic food web studies
  Yoshito Chikaraishi; Yuichiro Kashiyamal; Nanako O. Ogawa; Hiroshi Kitazato; Naohiko Ohkouchi
  MARINE ECOLOGY PROGRESS SERIES, 342, 85, 90, 2007, [Peer-reviewed]
  English, Scientific journal
• Massive melting of West Antarctic Ice Sheet during the latest pleistocene and holocene: Hydrogen isotopic records of sedimentary biomarkers in Ross Sea
  N. Ohkouchi; M. Toyoda; Y. Yokoyama; H. Miura; Y. Chikaraishi; H. Tokuyama; H. Kitazato
  GEOCHIMICA ET COSMOCHIMICA ACTA, 70, 18, A453, A453, Aug. 2006, [Peer-reviewed]
  English
• Carbon and hydrogen isotope variation of plant biomarkers in a plant-soil system
  Yoshito Chikaraishi; Hiroshi Naraoka
  CHEMICAL GEOLOGY, 231, 3, 190, 202, Jul. 2006, [Peer-reviewed]
  English, Scientific journal
• A novel method to identify illegal diesel fuel, II: the use of [1-D] n-alkane with stable hydrogen isotope analysis
  Yaeko Suzuki; Takashi Korenaga; Yoshito Chikaraishi
  CHEMISTRY LETTERS, 35, 5, 532, 533, May 2006, [Peer-reviewed]
  English, Scientific journal
• Compound-specific nitrogen isotopic composition of amino acids from Omul fish in Lake Baikal: A new approach for studying biological nitrogen cycle in the lake
  Ogawa Nanako, O.; Chikaraishi Yoshito; Wada Eitaro; Kitazato Hiroshi; Ohkouchi Naohiko
  Abstracts of Annual Meeting of the Geochemical Society of Japan, 53, 232, 232, GEOCHEMICAL SOCIETY OF JAPAN, 2006
  We have determined nitrogen isotopic composition of amino acids in Omul fish scales collected from Lake Baikal during 1945-1995 to study the food web structure in the surface water of the lake.
• Novel method to identify illegal diesel fuel, I: use of adamantane or [1, 2-D2] n-tetradecane as chemical marker.
  Yaeko Suzuki; Shintaro Ishioka; Takashi Korenaga; Yoshito Chikaraishi
  Environmental sciences : an international journal of environmental physiology and toxicology, 13, 4, 207, 12, 2006, [Domestic magazines]
  English, Scientific journal, In this study, we demonstrated a new identification method of illegal diesel fuel using adamantane (tricyclo[3,3,1,1,(3,7)]decane) or [1, 2-D(2)] n-tetradecane as a potential chemical marker instead of coumarin. In a mixing system of diesel fuel with marker-labeled kerosene, the concentration of kerosene in the mixed oil is quantitatively determined using specific ion fragments of the markers using GC/MS analysis, in which the detection limit is 12.5 ng/microl for adamantane or 7.1 ng/microl for [1, 2-D(2)] n-tetradecane. Coumarin, the currently used chemical marker, can be easily removed by sulfuric acid treatment, which is a primal cause of environmental pollution due to the illicit disposal of the strong acidic by-product. However, adamantane and [1, 2-D(2)] n-tetradecane cannot be removed by sulfuric acid treatment. Thus, although the detection limit of adamantane and [1, 2-D(2)] n-tetradecane is higher by approximately one or two orders of magnitude than that of coumarin, they cannot be removed by sulfuric acid treatment. Therefore, adamantane and [1, 2-D(2)] n-tetradecane are strong candidates as potential markers instead of coumarin, leading to the prevention of the production of illegal diesel fuel and a reduction in environmental pollution.
• Carbon and hydrogen isotopic composition of sterols in natural marine brown and red macroalgae and associated shellfish
  Y Chikaraishi
  ORGANIC GEOCHEMISTRY, 37, 4, 428, 436, 2006, [Peer-reviewed]
  English, Scientific journal
• Chemotaxonomic significance of distribution and stable carbon isotopic composition of long-chain alkanes and alkan-1-ols in C-4 grass waxes
  Florian Rommerskirchen; Anna Plader; Geoffrey Eglinton; Yoshito Chikaraishi; Juergen Rullkoetter
  ORGANIC GEOCHEMISTRY, 37, 10, 1303, 1332, 2006, [Peer-reviewed]
  English, Scientific journal
• Carbon and hydrogen isotopic compositions of sterols from riverine and marine sediments
  Y Chikaraishi; Y Yamada; H Naraoka
  LIMNOLOGY AND OCEANOGRAPHY, 50, 6, 1763, 1770, Nov. 2005, [Peer-reviewed]
  English, Scientific journal
• delta C-13 and delta D identification of sources of lipid biomarkers in sediments of Lake Haruna (Japan)
  Y Chikaraishi; H Naraoka
  GEOCHIMICA ET COSMOCHIMICA ACTA, 69, 13, 3285, 3297, Jul. 2005, [Peer-reviewed]
  English, Scientific journal
• Hydrogen, carbon and nitrogen isotopic fractionations during chlorophyll biosynthesis in C3 higher plants.
  Chikaraishi Y; Matsumoto K; Ogawa NO; Suga H; Kitazato H; Ohkouchi N
  Phytochemistry, 66, 8, 911, 920, 8, Apr. 2005, [Peer-reviewed]
• Hydrogen isotopic fractionations during desaturation and elongation associated with polyunsaturated fatty acid biosynthesis in marine macroalgae
  Y Chikaraishi; Y Suzuki; H Naraoka
  PHYTOCHEMISTRY, 65, 15, 2293, 2300, Aug. 2004, [Peer-reviewed]
  English, Scientific journal
• Hydrogen and carbon isotopic fractionations of lipid biosynthesis among terrestrial (C3, C4 and CAM) and aquatic plants
  Y Chikaraishi; H Naraoka; Poulson, SR
  PHYTOCHEMISTRY, 65, 10, 1369, 1381, May 2004, [Peer-reviewed]
  English, Scientific journal
• Carbon and hydrogen isotopic fractionation during lipid biosynthesis in a higher plant (Cryptomeria japonica)
  Y Chikaraishi; H Naraoka; Poulson, SR
  PHYTOCHEMISTRY, 65, 3, 323, 330, Feb. 2004, [Peer-reviewed]
  English, Scientific journal
• Compound-specific delta D-delta C-13 analyses of n-alkanes extracted from terrestrial and aquatic plants
  Y Chikaraishi; H Naraoka
  PHYTOCHEMISTRY, 63, 3, 361, 371, Jun. 2003, [Peer-reviewed]
  English, Scientific journal
• Organic hydrogen-carbon isotope signatures of terrestrial higher plants during biosynthesis for distinctive photosynthetic pathways
  Y Chikaraishi; H Naraoka
  GEOCHEMICAL JOURNAL, 35, 6, 451, 458, 2001, [Peer-reviewed]
  English, Scientific journal

• Stable isotope analysis-1: MassWorks on conventional gas chromatograph-mass spectrometer
  力石嘉人; 滝沢侑子; 布浦拓郎, 低温科学, 79, 2021
• Stable isotope analysis-1: gas chromatograph-isotope ratio mass spectrometer
  滝沢侑子; 力石嘉人, 低温科学, 79, 2021
• Identification of CO₂ fixation pathway of a thermophilic bacterium using a position-specific stable isotope probing
  千葉洋子; 千葉洋子; 澄田智美; 力石嘉人; 布浦拓郎, 日本農芸化学会大会講演要旨集(Web), 2020, 2020
• Omnivory in bees: Elevated trophic positions among all major bee families
  Shawn A. Steffan; Prarthana S. Dharampal; Bryan N. Danforth; Hannah R. Gaines-Day; Yuko Takizawa; Yoshito Chikaraishi, American Naturalist, 194, 3, 414, 421, 01 Sep. 2019
  University of Chicago Press, English, Report scientific journal
• What is the parasitic nematode Anisakis doing in host fish?
  菅谷智司; 菅谷智司; 滝沢侑子; 力石嘉人; 力石嘉人, Researches in Organic Geochemistry, 35, 1/2, 2019
• 好熱性水素酸化細菌の代謝から 生命の起源に迫る
  布浦 拓郎; 力石 嘉人; 跡見 晴幸, 現代化学 = Chemistry today, 569, 57, 61, Aug. 2018
  東京化学同人, Japanese
• 駿河湾深海域より発見した巨大セキトリイワシの1種
  河戸勝; POULSEN Jan Yde; 土田真二; 井田齊; 力石嘉人; 力石嘉人; 大河内直彦; 小栗一将; 後藤慎平; 小澤元希; 小澤元希; 田中彰; 宮正樹; 佐土哲也; 藤倉克則; 藤原義弘, ブルーアースサイエンス・テク要旨集, 2018, 2018
• 軟体動物殻体化石におけるアミノ酸の保存性:地質時代の海洋生態系の復元に向けた基礎研究
  兀橋大二郎; JENKINS Robert G.; 後藤(桜井)晶子; 力石嘉人; 長谷川卓, 日本古生物学会例会講演予稿集, 167th, 2018
• 深海生態系におけるトップ・プレデターの機能に関する研究
  藤原義弘; 土田真二; 河戸勝; 笠井彩香; 高橋幸愛; 屋良由美子; 福場辰洋; 渡邊佳孝; 吉田弘; 力石嘉人; 大河内直彦; 加藤千明; 藤倉克則; 増田殊大; 巻俊宏; 後藤慎平; 後藤慎平; 山中寿朗; 大西雄二; 田中彰, ブルーアース要旨集, 2016, 2016
• 個別アミノ酸窒素同位体比を用いた栄養段階推定法は化石に応用できるのか?~初期続成が及ぼす殻体内アミノ酸の変質に着目して~
  兀橋大二郎; JENKINS Robert; 後藤(桜井)晶子; 力石嘉人; 長谷川卓, 日本地球惑星科学連合大会予稿集(Web), 2016, 2016
• 底生有孔虫Planoglabratella opercularisにみられる盗葉緑体の獲得機構と殻形成に与える影響
  土屋正史; 宮脇省次; 力石嘉人; 小栗一将; 豊福高志; 多米晃裕; 植松勝之; 竹田晃治; 坂井宥哉; 三宅裕志; 大河内直彦; 丸山正, 日本古生物学会年会講演予稿集, 2015, 19, 26 Jun. 2015
  Japanese
• 深海域におけるトップ・プレデターに関する研究
  藤原義弘; 土田真二; 河戸勝; 福場辰洋; 渡邊佳孝; 吉田弘; 笠井彩香; 高橋幸愛; 後藤慎平; 力石嘉人; 大河内直彦; 加藤千明; 藤倉克則; 増田殊大; 巻俊宏; 田中彰, ブルーアース要旨集, 2015, 2015
• 液体クロマトグラフィを用いた遺跡出土骨試料の単離アミノ酸の放射性炭素年代測定
  板橋悠; 高野淑識; 力石嘉人; 小川奈々子; 大河内直彦; 山根雅子; 横山祐典; 米田穣, 日本文化財科学会大会研究発表要旨集, 32nd, 2015
• シチヨウシンカイヒバリガイ共生系は実験室でも化学合成できた!
  長井裕季子; 豊福高志; 野牧秀隆; 力石嘉人; 和辻智郎; 生田哲郎; 高木善弘; 吉田尊雄; 滋野修一; 井上広滋; 小西正朗, 日本地球惑星科学連合大会予稿集(Web), 2015, ROMBUNNO.BPT24‐06 (WEB ONLY), 2015
  Japanese
• Illustration of food web structure based on stable isotopic composition of amino acids
  力石 嘉人, バイオサイエンスとインダストリー, 72, 5, 390, 394, 2014
  バイオインダストリー協会, Japanese
• O12-12 嫌気性水素酸化好熱細菌Thermosulfidibacterの可逆的TCA回路(口頭発表)
  布浦 拓郎; 高木 善弘; 力石 嘉人; 森 浩二; 佐藤 喬章; 原田 健史; 柳川 勝紀; 首藤 彩; 大河内 直彦; 跡見 晴幸; 藤田 信之; 高井 研, 日本微生物生態学会講演要旨集, 2014, 88, 88, 2014
  日本微生物生態学会, Japanese
• 嫌気環境下における底生有孔虫細胞内での脱窒と微生物の関与
  野牧秀隆; 力石嘉人; 土屋正史; 豊福高志; 大河内直彦; 植松勝之; 多米晃裕; 北里洋, 日本古生物学会年会講演予稿集, 2013, 24, 28 Jun. 2013
  Japanese
• アミノ酸窒素同位体比を用いた、陸域分解系における土壌動物の資源利用解析
  陀安一郎; 長谷川尚志; 由水千景; 力石嘉人; 小川奈々子; 大河内直彦, 日本生態学会第60回大会, 2013
  Japanese
• 日本周辺の深海化学合成生態系に生息するシンカイヒバリガイ属とエラウロコムシ亜科の共生について
  高橋幸愛; 三宅裕志; 力石嘉人; 土屋正史; 渡部裕美; 丸山正; 藤倉克則, ブルーアース要旨集, 2013, 72, 2013
  Japanese
• 元素分析計‐同位体比質量分析計による有機物標準試料の炭素・窒素・酸素安定同位体比分析の試験所間比較
  鈴木彌生子; 力石嘉人; 山田桂大; 吉田尚弘, 日本分析化学会年会講演要旨集, 61st, 87, 05 Sep. 2012
  Japanese
• The diet and subsistence of Jomon hunter-gatherers in light of isotope ecology.
  Yoneda Minoru; Gakuhari Takashi; Naito Yuichi I; Chikaraishi Yoshito; Ohkouch Naohiko, Abstracts of Annual Meeting of the Geochemical Society of Japan, 59, 0, 2012
  遺跡から出土する古人骨や動物骨には、生前の生活に関する様々な痕跡が残されている。これらの情報は、物質文化を中心に研究がすすめられてきた考古学では得られない様々な人間活動の直接的な証拠として、近年注目を集めている。本報告では、縄文時代の古人骨、動物骨における地球化学的な分析から、現在どのような議論が行われているかを紹介し、新たな分析手法の応用の可能性について議論したい。縄文時代は、温暖化した完新世の環境のなかで農耕や牧畜といった食料生産を主要な生業にすることなく適応することができた定住的な社会として注目されている。１万年以上にわたる期間、亜寒帯から温帯、亜熱帯にまで拡散した縄文文化をもった人類集団の生業活動について、その多様性や地域性を同位体生態学的な視点から検討する。また、アミノ酸レベルでの同位体分析から見えてきた新しい生活様式についても紹介する。, GEOCHEMICAL SOCIETY OF JAPAN, Japanese
• 古人骨および動物遺存体のアミノ酸窒素同位体比分析について
  内藤裕一; 力石嘉人; 大河内直彦; 米田 穣, 佐久考古通信, 111, 17, 18, 2012
  Japanese
• Nitrogen isotopic composition and D/L ratio of amino acids in deep-subsurface marine sediments
  Yamaguchi Yasuhiko; Takano Yoshinori; Chikaraishi Yoshito; Suga Hisami; Ogawa Nanako; Yokoyama Yusuke; Ohkouchi Naohiko, Abstracts of Annual Meeting of the Geochemical Society of Japan, 59, 0, 2012
  本研究では、2009年の地球深部探査船「ちきゅう」の訓練期間中に房総半島沖で掘削された海洋堆積物コア試料（掘削深度230mbsf）について、全加水分解性アミノ酸および間隙水中溶存態アミノ酸に分け、D/L比と化合物レベル窒素同位体組成の深度分布を報告する。全加水分解性アミノ酸と比較して、間隙水中溶存態アミノ酸D/L比はアラニンでは一貫して高く、グルタミン酸では近い値を示した。アミノ酸窒素同位体組成に関しても、アラニンでは間隙水中溶存態アミノ酸が一貫して高い値を示し、グルタミン酸では全加水分解性と間隙水中溶存態のアミノ酸が近い値を示した。これらの結果を、他の化学成分（アンモニア、硫酸、メタンなど）の濃度分布や、アミノ酸窒素同位体組成に関する微生物培養実験の結果と合わせ、海洋堆積物深部におけるアミノ酸および有機物の動態に関して議論する。, GEOCHEMICAL SOCIETY OF JAPAN, Japanese
• アミノ酸窒素同位体比による陸域腐食食物網解析の試み
  長谷川尚志; 力石嘉人; 小川奈々子; 大河内直彦; 陀安一郎, 2012
  Japanese
• Symbiosis of Bathymodiolus mussels with scale-worm Branchipolynoe pettibone from hydrothermal vents and seeps in Japanese coast waters.
  Yoshimi Takahashi, Abstracts of Annual Meeting of the Geochemical Society of Japan, 59, 0, 187, 187, 2012
  深海化学合成生態系に固有なシンカイヒバリガイ属Bathymodiolus二枚貝は外套腔にエラウロコムシ亜科Branchipolynoe の多毛類を共生させている．本研究ではエラウロコムシ類のサイズ，性比，食性からエラウロコムシ類の生活史や宿主との相互作用の解明を目的とした．相模湾初島沖，沖縄トラフの試料を使用，共生率を推定し，グルタミン酸，フェニルアラニンのアミノ酸窒素同位体比から栄養段階を推定，両種の被食－捕食関係を推定した.エラウロコムシ類の栄養段階は，共生する9 mm以下の個体は約2.6，共生する9 mm以上の個体は約2.2， 宿主は約1.1であったことからネッスイエラウロコムシは体長9 ~10 mmを境に宿主への長期的な共生を開始し，宿主を摂食し始めると推測された．, GEOCHEMICAL SOCIETY OF JAPAN, Japanese
• 科学通信 分子で地球を読む(No.2)琵琶湖の富栄養化と生態系の変化
  大河内 直彦; 小川 奈々子; 力石 嘉人, 科学, 81, 7, 621, 623, Jul. 2011
  岩波書店, Japanese
• 縄文人の食性：新しい方法論からの視点
  大河内直彦; 内藤裕一; 力石嘉人; 米田 穣, 科学, 81, 11, 1116, 1117, 2011
  Japanese
• Nitrogen isotopic signatures of amino acids in microbes: culture experiments and applications to marine sediments
  Yamaguchi Yasuhiko; Takano Yoshinori; Chikaraishi Yoshito; Ogawa Nanako; Imachi Hiroyuki; Suga Hisami; Yokoyama Yusuke; Ohkouchi Naohiko, Abstracts of Annual Meeting of the Geochemical Society of Japan, 58, 0, 92, 92, 2011
  アミノ酸窒素同位体組成を環境中微生物代謝の指標として確立すべく、3ドメインを含む5種類の微生物を、特定の窒素源のもとで培養し、そのアミノ酸窒素同位体組成を調べた。すると、微生物がアミノ酸を新規合成する条件では、藻類等と似たアミノ酸窒素同位体組成相対パターンを示し、微生物がアミノ酸を培地から取り込む条件では、動物と近い15N濃縮係数を示した。温度、pH、塩分など生育環境の影響は見られなかった。つまりアミノ酸窒素同位体組成 のパターン・変動ルールが、三つのドメインにまたがる様々な生物間で共通である可能性が示唆された。また、日本近海（秋田沖、房総半島沖など）で海底堆積物を採取し、様々な画分（全加水分解成分、遊離成分など）のアミノ酸の量・組成・窒素同位体組成を分析した。それらの結果を、上記培養実験の結果をもとに解釈し、海底堆積物中の微生物代謝を推察した。, GEOCHEMICAL SOCIETY OF JAPAN
• 陸域腐食食物網へのアミノ酸窒素同位体比の適用
  長谷川尚志; 力石嘉人; 小川奈々子; 大河内直彦; 陀安一郎, 日本生態学会第58回大会, 2011
  Japanese
• Food chain analysis by nitrogen isotopic composition of amino acids(Geochemistry of organic matter, microbes, and ecosystem)
  CHIKARAISHI Yoshito; OGAWA Nanako O; TAKANO Yoshinori; TSUCHIYA Masashi; OHKOUCHI Naohiko, Chikyukagaku, 44, 4, 233, 241, 25 Dec. 2010
  Nitrogen isotopic composition (δ^<15>N) of individual amino acids has recently been employed as a potential powerful method for estimating the trophic level of organisms in food webs. In metabolic processes, one group of amino acids has little change in their nitrogen isotopic composition (e.g., 0.4‰ for phenylalanine), although another group has a large isotopic fractionation (e.g., 8.0‰ for glutamic acid). This fractionation could be associated with the cleavage of carbon-nitrogen bond in the metabolic processes (e.g., transamination) of amino acids. Therefore, a comparison between δ^<15>..., The Geochemical Society of Japan, Japanese
• Compound-specific stable carbon isotope analysis of lignin phenols by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS)
  SONODA Kazuhiko; TAKAHASHI Masashiro; CHIKARAISHI Yoshito; YAMAMOTO Shuichi, Researches in organic geochemistry, 26, 115, 122, 24 Dec. 2010
  This study demonstrates the stable carbon isotope analysis of individual lignin phenols based on off-line degradation and derivatization by tetramethylammonium hydroxide (TMAH) thermochemolysis, semi-purification by high-performance liquid chromatography (HPLC), compound-specific isotope analysis (CSIA) by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS), and isotope effect correction by isotope mass balance calculation. In GC/C/IRMS, we obtained the following optimal conditions to accurately and precisely determine the isotopic composition: combustion temperature of 1000℃, He carrier flow rate of 1.6mL min^<-1>, and injection amount of lignin phenols of 30-140ng. HPLC semi-purification using a normal-phase silica column with a column oven (at 30℃) can achieve baseline-separation of individual lignin phenols on the GC chromatogram without isotopic fractionation. Isotopic fractionation during TMAH derivatization can be corrected by the logarithmic correlation between the isotopic composition of the incorporated carbon during TMAH derivatization and the ratio of relative abundance between lignin phenols and TMAH reagents. By using this method, the carbon isotopic composition of individual lignin phenols can be determined within a standard deviation (1σ) of 0.2‰-0.9‰, making this method suitable for molecular isotope studies in the field of organic geochemistry., The Japanese Association of Organic Geochemists, English
• Preface to "Advances in molecular and stable isotope studies among the organic geochemical and related communities"(Advances in molecular and stable isotope studies among the organic geochemical and related communities (Part I))
  Chikaraishi Yoshito; Oba Yasuhiro, Researches in organic geochemistry, 26, 1, 1, 24 Dec. 2010
  The Japanese Association of Organic Geochemists, Japanese
• Quality control by wet chemical pre-treatment for precise compound-specific isotope analysis
  TAKANO Yoshinori; CHIKARAISHI Yoshito; OHKOUCHI Naohiko, Researches in organic geochemistry, 26, 81, 93, 24 Dec. 2010
  Recent advances in the application of molecular approaches have emphasized our potentially underestimate of microbial diversity in natural environments and have revealed comprehensive biogeochemical processes. One of the biggest challenges for organic geochemists and/or microbial ecologists is to identify which organisms are carrying out a specific set of metabolic processes. To answer this fundamental question, stable isotope probing (SIP) together with compound-specific isotope analysis (CSIA) is a useful technique to understand the microbial ecology and its biogeochemical cycles. The method relies on the incorporation of a substrate that is highly enriched in a stable isotope such as ^<13>C and ^<15>N, and the identification of specific molecular targets through active microorganisms in any environment. However, we have to pay attention about highly SI-enriched contamination problems and co-elution problems during pretreatment of chemical analysis and also in chromatographic procedures, which potentially prevent us from performing precise CSIA. Here, we point out quality control by wet chemical pre-treatment for precise compound-specific isotope analysis by isotope-ratio mass spectrometry coupled to gas chromatography and liquid chromatography. Not only in biogeochemical background but also from a scope of common welfare, CSIA technique is also widely useful tools for validation approaches in food material, anti-doping test, and environmental assessment. For further precise CSIA, we also discuss representative optimized analytical conditions of some model compounds including intact polar lipids (IPLs) with its derivatives, n-alkane, and amino acids., The Japanese Association of Organic Geochemists, Japanese
• Tracking aquatic change using chlorin-specific carbon and nitrogen isotopes: The last glacial-interglacial transition at Lake Suigetsu Japan
  J. Tyler; Y. Kashiyama; N. Ohkouchi; N. Ogawa; Y. Yokoyama; Y. Chikaraishi; R.A. Staff; M. Ikehara; C. Bronk Ramsey; C. Bryant; F. Brock; K. Gotanda; T. Haraguchi; H. Yonenobu; T. Nakagawa; Suige; Project Members, Geochemistry Geophysics Geosystems, 11, Q09010, Sep. 2010
• Isotopomers of chlorophyll nuclei: Theory and application
  N. Ohkouchi; Y. Chikaraishi; Y. Kashiyama; N.O. Ogawa, In: N.Ohkouchi I. Tayasu K. Koba (eds.) Earth Life and Isotopes Kyoto University Press Kyoto, 271, 290, Aug. 2010
• Reconstructing the life history of modern and fossil nautiloids based on the nitrogen isotopic composition of shell organic matter and amino acids
  Y. Kashiyama; N.O. Ogawa; Y. Chikaraishi; N. Kashiyama; S. Sakai; K. Tanabe; N. Ohkouc, In: K. Tanabe Y. Shigeta T. Sasaki H. Hirano (eds.) Cephalopod-Present and Past, 67, 75, May 2010
• Further evaluation of the trophic level estimation based on nitrogen isotopic composition of amino acids
  CHIKARAISHI Y, Earth, life, and isotopes, 37, 51, 2010
  Kyoto University Press
• Reconstruction of ancient cold-seep activities based on biomarkers : A case study of Lower Pleistocene Ofuna and Koshiba Formation, central Japan
  Tsuboi Misato; Sato Yoko; Hamana Noriaki; Nakamura Eiko; Majima Ryuichi; Kitazato Hiroshi; Suga Hisami; Chikaraishi Yoshito; Kato Kazuhiro; Wada Hideki; Ohkouchi Naohiko, Fossils, 87, 0, 5, 21, 2010
  We analyzed lipid biomarkers related to AOM (anaerobic oxidation of methane) that happened in the early Pleistocene (1.7-1.4Ma) cold-seep site, northern part of Miura Peninsula, Pacific side of central Japan. Nineteen samples are obtained from a bedding-normal, 107m-long core consisting of the Koshiba (sandy mudstone and muddy sandstone, above 23m in core depth) and the Ofuna (mudstone, below 23m) Formations. In this core, both the chemoautotrophic bivalves (Lucinoma, Conchocele, Archarax) and ^<13>C-depleted authigenic carbonates (aragonite, MG-calcite, dolomite) occur abundantly. Four important results of this study are summarized as follows. 1) Both archaeal and sulfate reducing bacterial (SRB) biomarkers are recovered in all samples and their ether linkages are well preserved even in 1.7-1.4Ma sediments. 2) High activities of AOM are inferred in 7.1-7.6m and 14.6m in core depths where both archaeal and SRB-biomarkers are distinctly concentrated and greatly depleted in ^<13>C (δ^<13>C less than-100‰ vs. PDB). Those activities happened probably when marine bottoms were in 6.5-7m and 13-13.5m, respectively, where chemoautotrophic bivalves occur abundantly. 3) Two samples obtained from the same horizon 14.6m show an apparent difference in biomarker compositions. This difference may be attributed to a different micro habitats for microbes. 4) The occurrences of biomarkers derived from planktonic archaea are inferred from their δ^<13>C values and relative abundance of 4 kinds of biphytanes. Planktonic archaeal biomarkers are probably recovered from all samples and their concentration rates may be useful as an index of sedimentation rate., Palaeontological Society of Japan, Japanese
• Nitrogen isotopic signature of amino acids in microbes: a novel tool in biogeochemistry
  Yamaguchi Yasuhiko; Takano Yoshinori; Chikaraishi Yoshito; Ogawa Nanako; Imachi Hiroyuki; Suga Hisami; Yokoyama Yusuke; Ohkouchi Naohiko, Abstracts of Annual Meeting of the Geochemical Society of Japan, 57, 0, 115, 115, 2010
  本研究では、三つのドメイン（真核生物・バクテリア・アーキア）を含む5種類の微生物を、特定の窒素源のもとで培養し、そのアミノ酸窒素同位体組成を調べた。その結果、アミノ酸窒素同位体組成のパターン・変動ルールが、三つのドメインを含む様々な生物間で共通であることが示唆された。つまりアミノ酸窒素同位体組成は、微生物の現場における代謝（アミノ酸の合成もしくは分解）および生物地球化学的役割（特に窒素循環・有機物変質）を調べための、強力な手法になりうるだろう。, GEOCHEMICAL SOCIETY OF JAPAN
• Food web analyses of the marine ecosystems based on nitrogen isotope of amino acids
  Tsuchiya Masashi; Fujiwara Yoshihiro; Nomaki Hidetaka; Toyofuku Takashi; Yamamoto Hiroyuki; Maruyama Tadashi; Wada Eitaro; Chikaraishi Yoshito; Ohkouchi Naohiko; Takano Yoshinori; Ogawa Nanako; Fujikura Katsunori; Yoshida Takao; Kitamura Minoru; Lindsay Dhugal, Abstracts of Annual Meeting of the Geochemical Society of Japan, 57, 0, 41, 41, 2010
  海洋生態系は，様々な生物群集からなる構成されており，複雑な被食―捕食の生物間相互作用の上に成立しているため，その構造を明らかにすることは難しい。現在の海洋生態系は，様々な環境変遷を経てきた生物群集から構成されており，このような生物間の相互作用や進化を通して，現在の海洋生態系が形成されている。海洋生態系の構造を明らかにすることは，環境変化に対する生物の応答様式や温暖化に伴う海洋生態系の構造の変化の追跡，あるいは多様性の維持機構を明らかにする上でも非常に重要である。<br> アミノ酸の窒素同位体比に基づく栄養段階の推定法は，複雑な生態系の栄養段階を明瞭に示すことができる重要なツールである。この手法は，海洋研究開発機構で開発された新たなツールであり，栄養段階に伴い食物連鎖の上位の生物ほど15Nの濃縮が見られるアミノ酸（グルタミン酸など）と，栄養段階によらずほぼ一定の窒素同位体比を持つアミノ酸（フェニルアラニンなど）を用いることで，生物の栄養段階を正確に求めることを基盤技術としている。アミノ酸の窒素同位体比の変化は，生物個体内の代謝による同位体分別の影響により，栄養段階の上昇が生じるという生物の生理学的特性に起因しているため，同位体分別の背景を理解した上で栄養段階を推定できることに大きな利点がある。<br> われわれは，アミノ酸の窒素同位体比分析技術を用いて，海洋生態系のダイナミクスと生態系を構成する海洋生物の進化や共生現象を介した環境への適応様式を理解し，資源などのエネルギーが表層から底層への梯子を段階的に連鎖する「梯子モデル」が，どのように成立しているのかを検証する。具体的には，１）海洋生態系の構造を明らかにすること，２）海洋生物の共生系の仕組みを明らかにすることであり，前者では，被食―捕食の関係から食物網構造を明らかにするとともに，生態・生化学・進化生態学的な解析をあわせることで，海洋生態系の構造と役割，進化を明らかにする。後者では，遺伝子からその代謝機能を推定するとともに，共生系内での物質の流れを安定同位体から明らかにし，宿主あるいは共生生物の依存度を明らかにし，共生を介した生態や進化を理解することを目指している。 これまでに，海洋の化学合成生態系や光合成生態系などを構成する真核生物の栄養段階を推定するとともに，共生細菌などの共生生物と宿主との関係を窒素同位体比と遺伝子から得られた代謝機能との関係を推測した。相模湾の底層生態系では，甲殻類などが光合成生態系由来の生物に依存する生物を捕食するとともに，化学合成生態系に依存する生物を捕食する。このように底層生物は複数の生態系に依存した栄養摂取形態を持つと考えられ，各アミノ酸の窒素同位体比は，利用する資源の由来を推測できる可能性がある。また，冷湧水系の化学合成生態系では，海底下からの湧水に依存するため軽い窒素同位体比を持つのに対して，光合成生態系では重い値を示す。アミノ酸窒素同位体比は，各生態系における栄養段階を理解するだけではなく，光合成生物の化学合成系依存の割合を理解することもできる。発表では，相模湾を中心とする海洋生物のアミノ酸窒素同位体の結果とそれを基にした栄養段階について紹介する。, GEOCHEMICAL SOCIETY OF JAPAN
• 食性指標としてのアミノ酸窒素安定同位体比の利用：土壌食物網研究への適用にむけて
  長谷川尚志; 力石嘉人; 小川奈々子; 大河内直彦; 陀安一郎, 日本生態学会第57回大会, 2010
  Japanese
• Compound-specific stable hydrogen isotope analysis of small amount of organic compounds
  CHIKARAISHI Yoshito, Researches in organic geochemistry, 25, 29, 38, 30 Nov. 2009
  After the development of compound-specific isotope analysis (CSIA) by gas chromatograph/pyrolysis/isotope ratio mass spectrometer (GC/pyrolysis/IRMS) in the end of the 1990s, stable hydrogen isotopic composition of organic compounds has been employed for many fields of studies, particularly among the organic geochemical community as a powerful tool for tracing sources and delivery of organic compounds in geological and geographical samples and as a potential proxy for reconstructing paleoclimatic, paleohydrological, and paleosalinity changes. However, sample amount required for accurate and precise determination of the isotopic composition is generally 10-50nmol H for each compound, which is much larger than that of stable carbon (0.1-5nmol C) and nitrogen (1-10nmol N) on the isotope analysis by gas chromatograph/combustion/isotope ratio mass spectrometer (GC/combustion/IRMS). Here, I demonstrate the performance of GC/pyrolysis/IRMS on the small amount of samples, and suggest a mathematical correction for preventing systematic errors in the measured isotopic composition due to different sample amounts. By using this correction, the hydrogen isotopic composition of organic compounds can be determined with a standard deviation (1σ) of better than 7‰ on the sample amount of 4nmol H and even 13‰ on the sample amount of 2nmol H. This correction thus allows us easy access to the hydrogen isotopic composition of organic compounds containing with small concentration in samples., The Japanese Association of Organic Geochemists, Japanese
• GC/MS analysis of amino acids as pivaloyl/isopropylesters
  CHIKARAISHI Yoshito; TAKANO Yoshinori; OHKOUCHI Naohiko, Researches in organic geochemistry, 25, 61, 70, 30 Nov. 2009
  The Japanese Association of Organic Geochemists, Japanese
• Diet analysis based on the nitrogen isotopic composition of amino acids
  O OGAWA Nanako; CHIKARAISHI Yoshito; OHKOUCHI Naohiko, 臨床化学, 38, 3, 266, 271, 31 Jul. 2009
  Japanese
• Compound-specific nitrogen isotope analysis of amino acids: Implications of aquatic food web studies
  Y. Chikaraishi; N. O. Ogaw; N. Ohkouchi, GEOCHIMICA ET COSMOCHIMICA ACTA, 73, 13, A219, A219, Jun. 2009
  English, Summary international conference
• Dietary reconstruction of Jomon hunter-gatherers based on nitrogen isotopic composition of amino acid
  Naito Y; Chikaraishi Y; Ohkouchi N; Yoneda M, The 4th International Symposium on Isotopomers (ISI 2008) Proceedings, 4, 265, 267, 2008, [Peer-reviewed]
  English
• クロロフィルのアイソトポマー：理論と実践
  大河内 直彦; 力石 嘉人; 小川 奈々子; 柏山 祐一郎; 菅 寿美; 北里 洋, 日本地球化学会年会要旨集, 55, 0, 185, 185, 2008
  クロロフィルは光合成独立栄養生物によって合成され，生体内では光合成色素として機能している。このクロロフィルは，光合成細菌が合成するバクテリオクロロフィルまで含めると，大きく10種類に分類することができ，各クロロフィルは特定の起源光合成生物によってのみ合成されることが知られている。このクロロフィルの中心核のテトラピロール構造は，堆積物中で化学的にも微生物学的にも非常に安定したャ泣tィリンと呼ばれる化合物群として長期間保存されている。そのため，堆積岩から抽出されるャ泣tィリンの炭素および窒素安定同位体比は，クロロフィルの同位体組成，ひいては一次生産者の同位体組成を強く反映している。それらの情報は，潜在的に過去の光合成生物の栄養塩の起源，取り込み様式，代謝プロセスといった海洋学的，生物学的な情報を，ほぼ純粋な形で保存していると考えられる。本講演では，主にクロロフィルの分子内同位体組成（アイソトャ}ー）を決定する要因について，生合成の観点から考察し，それからどのような環境情報が引き出せるのかについて論じるとともに，実際の測定結果との整合性についても論じる。クロロフィルのテトラピロール構造は，葉緑体内でグルタミン酸８分子が縮合して生成されるため，その炭素同位体比はグルタミン酸のそれを強く反映したものである。ただし，縮合の過程でグルタミン酸のC5炭素が６つ脱離するため，正確に一致することはない(Ohkouchi et al., 2008)。テトラピロール構造の分子内炭素同位体組成のうち，各ピロール環を架橋している炭素については，クロロフィルを各ピロール環に分解（マレイミド化）することにより，マスバランスによって同位体組成を求めることができる。またクロロフィルの窒素同位体比は，グルタミン酸がアミノレブリン酸になるときに導入されるアンモニアの窒素同位体比を反映している。したがって，グルタミン酸の窒素同位体比とは一致しないはずであり，実際にそのことが実験から確認された。各ピロール環に含まれる窒素は，マレイミド化した後に測定したところ，理論どおりほぼ同じ同位体組成を持つことが明らかになった。, 一般社団法人日本地球化学会, Japanese
• Stable hydrogen isotopic composition of lipids and pigments
  CHIKARAISHI Yoshito, Researches in organic geochemistry, 22, 1, 18, 28 Dec. 2007
  Gas chromatograph/pyrolysis/isotope ratio mass spectrometer (GC/pyrolysis/IRMS) and pyrolysis elemental analyzer/isotope ratio mass spectrometer (pyrolysis-EA/IRMS) are relatively new instruments for on-line determination of stable hydrogen isotopic composition (D/H) of organic compounds, which allow easy and rapid access to their isotopic composition in various biological and geological samples. The hydrogen isotopic composition is a potential tool for the reconstruction of hydrological cycle in paleoenvironment. Combined with carbon isotopic composition (^<13>C/^<12>C), it has also been used for the evaluation of sources and delivery of organic compounds in geological as well as geographical samples. This paper reviews recent studies on the compound-specific hydrogen isotope analysis of lipids and pigments, which consists of brief summaries of (1) biological controls on the isotopic composition, (2) isotopic modification associated with biodegradation and diagenesis, and (3) its application in organic geochemistry., The Japanese Association of Organic Geochemists, Japanese
• 藻類・植物・堆積物に含まれるクロロ色素・フェオ色素のHPLC/MSによる解析
  Y. Chikaraishi; Y. Kashiyama; N. Ohkouchi, Researches in Organic Geochemistry, 22, 43, 55, Dec. 2007
• Stable Isotopes as Ecological Proxies : Compound-Specific Nitrogen Isotope Analysis of Amino Acids
  CHIKARAISHI Yoshito; KASHIYAMA Yuichiro; OGAWA Nanako O; OHKOUCHI Naohiko, Radioisotopes, 56, 8, 463, 477, 15 Aug. 2007
  日本アイソトープ協会, Japanese
• Stable nitrogen isotopic composition of amino acids: Implications for aquatic food web studies
  Y. Chikaraishi; Y. Kashiyama; N. O. Ogawa; H. Kitazato; N. Ohkouchi, GEOCHIMICA ET COSMOCHIMICA ACTA, 71, 15, A170, A170, Aug. 2007
  English, Summary international conference
• Reconstruction of the past biogeochemical cycles based on compound-specific N and C isotopic analyses of sedimentary porphyrins
  Y. Kashiyama; N. O. Ogawa; Y. Chikaraishi; S. Nomoto; R. Tada; H. Kitazato; N. Ohkouchi, GEOCHIMICA ET COSMOCHIMICA ACTA, 71, 15, A466, A466, Aug. 2007
  English, Summary international conference
• 有機化合物の分子レベル安定窒素同位体比分析による地球環境解析―2:アミノ酸
  力石嘉人; 柏山祐一郎; 小川奈々子; 高野淑識; 菅寿美; 豊福高志; 富谷朗子; 北里洋; 大河内直彦, 日本地球化学会年会講演要旨集, 54th, 158, 2007
  Japanese
• O-10 Reconstruction of surface ocean environment during the formation of black shales in the mid-Cretaceous based on sedimentary chlorophyll derivatives
  Ohkouchi N; Kashiyama Y; Chikaraishi Y; Ogawa N. O; Kuroda J; Kitazato H, Annual Meeting of the Geological Society of Japan, 113, 48, 48, 08 Sep. 2006
  The Geological Society of Japan, Japanese
• Nitrogen isotopic composition of chlorophylls and porphyrins in geological samples as tools for reconstructing paleoenvironment
  N. Ohkouchi; Y. Kahiyama; Y. Chikaraishi; N. O. Ogawa; R. Tada; H. Kitazato, GEOCHIMICA ET COSMOCHIMICA ACTA, 70, 18, A452, A452, Aug. 2006
  English, Summary international conference
• Nitrogen and carbon isotopic analyses on sedimentary porphyrins of organic-rich shales from Miocene and mid-Cretaceous
  Y. Kashiyama; N. O. Ogawa; Y. Chikaraishi; H. Suga; R. Tada; H. Kitazato; N. Ohkouchi, GEOCHIMICA ET COSMOCHIMICA ACTA, 70, 18, A306, A306, Aug. 2006
  English, Summary international conference
• Stable nitrogen isotope analysis of chlorophylls by gas chromatography-isotope ratio mass spectrometry
  Y. Chikaraishi; Y. Kashiyama; N. O. Ogawa; H. Kitazato; S. Nomoto; N. Ohkouchi, GEOCHIMICA ET COSMOCHIMICA ACTA, 70, 18, A100, A100, Aug. 2006
  English, Summary international conference
• 国産コシヒカリの多元素安定同位体比分析と産地特定の可能性
  鈴木彌生子; 力石嘉人; 小川奈々子; 大河内直彦; 伊永隆史, 分析化学討論会講演要旨集, 67th, 45, 29 Apr. 2006
  Japanese
• Stable carbon and nitrogen compositions of photosynthetic pigments as tracers for elemental cycle in the modern- and paleo-environments
  N. Ohkouchi; Y. Nakajima; N.O. Ogawa; H. Suga; Y. Kashiyama; K. Matsumoto; Y. Chikaraishi; K. Oguri; H. Kitazato, Frontier Research on Earth Evolution, 2, 1, 4, 2006
• Nitrogen and carbon isotopic analyses on sedimentary porphyrins as a proxy for the paleo-photoautotrophs
  Kashiyama Yuichiro; Ogawa Nanako O; Chikaraishi Yoshito; Suga Hisami; Nomoto Shinya; Tada Ryuji; Kitazato Hiroshi; Ohkouchi Naohiko, Abstracts of Annual Meeting of the Geochemical Society of Japan, 53, 0, 20, 20, 2006
  堆積物中から抽出されるポルフィリン化合物（化石ポルフィリン）は、光合成生物が普遍的に合成するクロロフィルやバクテリオクロロフィルを起源とする。よってその安定同位体組成は、過去の環境中の物質循環や、光合成生物の代謝活動を直接的に記録したものであり、過去の海洋表層の物質循環を理解する上で有力な指標となりうる。本研究では、化石ポルフィリンを高速液体クロマトグラフィーを用いて単離・精製し、分析感度を向上させた元素分析計／同位体質量分析計を用いて測定する手法を確立した。また、単離した化石ポルフィリンを酸化分解してマレイミド化を行い、ガスクロマトグラフ／燃焼／同位体質量分析計を用いて、極微量のポルフィリンについても窒素同位体組成を測定することに成功した。また、中部中新統女川層（12～10Ma）及びイタリアの白亜系黒色頁岩（海洋部酸素事変；OAE-2）の分析結果に基づき、堆積当時の海洋環境について論じる。, GEOCHEMICAL SOCIETY OF JAPAN
• Compound-specific stable nitrogen isotope analysis of amino aicds by GC/C/IRMS: elucidation for biological isotopic fractionation of amino acid nitrogen and its application for ecological studies
  Chikaraishi Yoshito; Kashiyama Yuichiro; Tada Yohei; Toyohuku Takashi; Ogawa Nanako; Kitazato Hiroshi; Ohkouchi Naohiko, Abstracts of Annual Meeting of the Geochemical Society of Japan, 53, 0, 231, 231, 2006
  生体試料の全窒素同位体比（SUP15/SUPN/SUP14/SUPN）は、食物連鎖における栄養段階の上昇に伴い約3パーミルずつ高くなることが経験的に知られており、この知見は生態系の食物連鎖網や窒素サイクルの解析に広く用いられてきた。しかし、この窒素同位体比変動（SUP15N/SUP濃縮）の詳細なメカニズムはほとんどわかっていない。BRそこで本研究では、藻類と捕食動物に含まれる12種類のアミノ酸の窒素同位体比を調査した結果から、生体アミノ酸の窒素同位体比変動を明らかにし、食物連鎖における窒素同位体比変動メカニズムを考察した。発表ではさらに、この結果を応用した生態学研究をいくつか紹介し解説する。, GEOCHEMICAL SOCIETY OF JAPAN
• Compound-Specific Hydrogen and Carbon Isotope Analysis and its Application to Natural Samples
  CHIKARAISHI Yoshito; NARAOKA Hiroshi, ぶんせき, 356, 456, 462, 05 Aug. 2004
  日本分析化学会, Japanese
• Carbon and hydrogen isotopic compositions of sterols in riverine-marine sediments
  Y Chikaraishi; H Naraoka, GEOCHIMICA ET COSMOCHIMICA ACTA, 68, 11, A338, A338, Jun. 2004
  English, Summary international conference
• Carbon and hydrogen isotopic fractionations during lipid biosyntheses in higher plants
  Y Chikaraishi, GEOCHIMICA ET COSMOCHIMICA ACTA, 67, 18, A64, A64, Sep. 2003
  English, Summary international conference
• Carbon isotope fractionation of monoaromatic hydrocarbons and chlorinated ethylenes during oxidation by Fenton's reagent
  Poulson, SR; Y Chikaraishi; H Naraoka, GEOCHIMICA ET COSMOCHIMICA ACTA, 67, 18, A382, A382, Sep. 2003
  English, Summary international conference
• Stable Hydrogen Isotope Analysis of Individual Biomolecules and Its Application to Geochemistry and Environmental Science
  NAKAMURA Hiroshi; CHIKARAISHI Yoshito, Radioisotopes, 51, 6, 249, 250, 15 Jun. 2002
  Japanese

• 古気候変動学特論, 2024年, 修士課程, 環境科学
• 大学院共通授業科目（一般科目）：自然科学・応用科学, 2024年, 修士課程, 大学院共通科目
• 環境分析化学特論, 2024年, 修士課程, 環境科学
• 生態系物質循環学特論, 2024年, 修士課程, 環境科学院
• 生物地球科学特論, 2024年, 修士課程, 環境科学
• 生態系環境科学特論, 2024年, 修士課程, 環境科学院
• 環境と人間, 2024年, 学士課程, 全学教育
• 一般教育演習(ﾌﾚｯｼｭﾏﾝｾﾐﾅｰ), 2024年, 学士課程, 全学教育

• 隕石によって供給される生命材料分子とその起源
  科学研究費助成事業
  01 Apr. 2026 - 31 Mar. 2030
  古川 善博; 古賀 俊貴; 力石 嘉人
  日本学術振興会, 基盤研究(A), 東北大学, 26H02079
• Isotope analysis of organic compounds: development of a method for solving isotopic alteration associated with derivatization
  Grants-in-Aid for Scientific Research
  30 Jun. 2023 - 31 Mar. 2026
  力石 嘉人
  有機化合物の安定同位体比の解析は，地球生命科学分野の様々な研究で広く用いられ，これまでに膨大な研究成果をもたらしてきた。しかしながら，本解析法は，測定法が開発されてから約30年が経った現在においても，適応できる有機化合物の種類が極めて少ないという欠点を持つ。それは，アミノ酸，糖，核酸塩基などの多くの主要な有機化合物で「同位体比の測定を行うために必要な誘導体化に伴い，同位体比の人為的改変が起きてしまう」という課題が未だに解決できていないためである。そこで本研究では，「誘導体基の交換反応」という新しいアイデアを導入し，この長年の課題を抜本的に解決する革新的技術の開発にチャレンジする。
  研究の初年度（令和5年度）は，アミノ酸の安定炭素同位体比の分析を対象に「少量の誘導体化剤」＋「十分量のエステル系溶媒を用いた交換反応」を組み合わせ，「誘導体化に伴う同位体比の人為的改変の解決法」を開発に挑戦した。
  誘導体化剤や交換に用いるエステル系溶媒，交換反応の時間等を変えた様々な条件での交換反応を実施した結果，アシル-イソプロピル誘導体化に対して酢酸イソプロピルを用いて交換反応を行った場合，交換反応を行わない場合の測定精度がプラスマイナス8パーミルであったのに対し，交換反応を4時間行うと，測定精度がプラスマイナス2パーミル程度に減少することが証明された。この結果をもとに，現在さらなる条件検討を実施している。
  Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Research (Pioneering), Hokkaido University, 23K17312
• Elucidation of the mechanism of high fish growth rate brought by artificial breeding water
  Grants-in-Aid for Scientific Research
  01 Apr. 2023 - 31 Mar. 2026
  小濱 剛; 力石 嘉人
  本研究の達成目標は，天然の飼育水（淡水あるいは海水）と好適環境水で様々な魚類を飼育し，アミノ酸の安定同位体比（15N/14N）を異なる飼育水の間で比較することにより，飼育個体の「エネルギー消費量」を定量的に評価することである。
  2023年度は，浸透圧調節機能が異なる３タイプ（トラフグなどの狭塩性の海水魚，コイなどの狭塩性の淡水魚，ウナギなどの広塩性の通し回遊魚）から，狭塩性の淡水魚代表種を選定した。また，選定した魚種について塩分の異なる好適環境水（0・4・8‰）での比較飼育試験を行い，体重・体長の時系列変化に加え，飼育水質のモニタリングを継続して実施している。飼育60日目時点における結果から，体重・体長共に0‰（体重2.25±0.85g,体長53.81±7.83mm）と8‰（体重1.36±0.43g,体長44.99±5.42mm），4‰(体重2.70±0.75g,体長56.03±6.94mm)と8‰に統計的優位差が確認された。この結果から，狭塩性の淡水魚代表種については，塩分4‰以下の好適環境水であれば、長期飼育が可能であると示唆された。
  今後は，飼育試験を継続するとともに，飼育試験中の個体を適宜抜粋し，アミノ酸の安定同位体比（15N/14N）の測定を行うことで，飼育個体の「エネルギー消費量」を定量的に評価し、成長差との整合性を確認する予定である。
  なお、比較飼育試験における途中結果については，研究分担者と適宜情報共有を行っており，好適環境水を用いることによる科学的効果の解明についても，両者で議論を重ねている。
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Chiba Institute of Science, 23K11525
• Elucidation of variation in marine primary production and biogeochemical linkages between land and ocean in North Pacific Ocean during the Neogene
  Grants-in-Aid for Scientific Research
  01 Apr. 2022 - 31 Mar. 2026
  沢田 健; 桑田 晃; 力石 嘉人; 入野 智久; 加藤 悠爾
  本研究では、深海掘削および陸上調査によって得られた新第三紀堆積物から、藻類および陸上植物の分子化石（バイオマーカー）、藻類微化石、生物源シリカを分析し、新生代の北太平洋におけるグローバルな海洋ー陸域間の生物地球化学的循環と生態系の連鎖（リンケージ）、環境気候システムとの関連性を解明する。海洋・陸域生態系が駆動する長時間スケールの物質循環システムの解明という観点から、海洋基礎生産と陸源有機物の海洋への輸送量の変動の体系的で定量性の高い復元を目指す。さらに、新しい古環境復元法を確立するため、新規の藻類バイオマーカーの探索とその解析法、陸上植物バイオマーカーの分子内同位体比解析法を開発する。2022年度における主な研究成果は次のとおりである。
  1. 北部北太平洋アラスカ湾掘削コア（U1417）のバイオマーカー分析を行い、珪藻、ハプト藻、渦鞭毛藻、真正眼点藻などに由来するバイオマーカーを検出し、低分解能で大まかではあるが過去1000万年間の海洋基礎生産変動を復元した。また、ハプト藻由来の長鎖アルケノンおよび真正眼点藻由来の長鎖アルキルジオールを用いた古水温計によって海洋表層水温の変動を復元した。これらの水温の変動パターンは概ねよく一致し、全体的には中新世以降の全球的な寒冷化傾向を示すことがわかった。
  2. 北海道中南部の日高町などに分布する中新統荷菜層における泥質堆積岩から、陸上セクションからは極稀な長鎖アルケノンが検出されることを発見した。そのアルケノン古水温計を用いて中期～後期中新世における体系的な海洋表層水温と海洋基礎生産の変動を復元した。
  3. 陸源有機物において陸上植物だけでなく菌類のような生物のバイオマーカーにも着目し、特に地衣類の生体試料を用いて、新規のバイオマーカーを検討した。その結果、ファルネンなどのテルペノイドがそのバイオマーカーになり得ることを明らかにした。
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 23K22610
• Elucidation of the variation in marine primary production and the land-ocean biogeochemical linkage in North Pacific Ocean
  Grants-in-Aid for Scientific Research
  01 Apr. 2022 - 31 Mar. 2026
  沢田 健; 桑田 晃; 力石 嘉人; 入野 智久; 加藤 悠爾
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 22H01339
• Development of GC-GC-IRMS
  Grants-in-Aid for Scientific Research
  01 Apr. 2020 - 31 Mar. 2024
  力石 嘉人; 古川 善博; 滝沢 侑子
  本研究では，2次元ガスクロマトグラフ-安定同位体比質量分析計（GC-GC-IRMS）を開発する。その目的は，従来の1次元GC-IRMSを用いた測定において，長年の課題であった「GCでの厳格なピーク分離の要求」を抜本的に解決すること，そして，従来法では測定不可能であった多々の試料に関して，有機化合物の安定同位体比測定を可能にすることである。その達成は，生物から環境試料まで，試料中の全ての有機化合物について5W2H（Who, What, When, Where, Why, How, How many）に関する定性・定量的情報を獲得し，地球惑星科学の多様な研究，とくに (i) 生物の生合成・代謝系の機能の研究，(ii) 地球生物圏における有機物・エネルギー循環の研究，(iii) 宇宙空間や初期地球における有機物生成や生命の起源の研究などで，ブレイクスルーをもたらすと期待できる。
  本年度（繰り越し期間を含む）は，購入したGC-GCモジュール」部を，研究代表者の研究室が現有している「GC-IRMS」と接続し，「GC-GC-IRMS」を組み立てた。また，有機化合物の安定同位体比の測定に向けて，(1) 接続部，ガスライン，キャピラリーラインの再設計や再配置，(2) 様々な条件（導入部の圧力・温度等のプログラム，GC部の温度プログラム，キャリアーガスの流速，溶媒の除去とIRMSへの接続のタイミングなど）に関して，様々な検証・最適化を実施した。これらの大部分は，当初，初年度に行う予定であったが，新型コロナウィルスの感染拡大防止措置のため実施が困難であっため，研究費の繰り越しを申請し，期間を延長して行った。
  検証・最適化を行うなかで，「GC-GCモジュールと燃焼炉の間の温度制御の不安定性」が重要な課題であることがわかり，これを翌年の課題とした。
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), Hokkaido University, 20H00185
• Large scale mapping of marine pollution risk using seabirds as a standardized sampling device
  Grants-in-Aid for Scientific Research
  01 Apr. 2019 - 31 Mar. 2024
  綿貫 豊; 依田 憲; 石塚 真由美; 力石 嘉人; 高田 秀重
  本研究は、バイオロギング（ジオロケーター）で海鳥多数個体を通年追跡し，集中利用場所（生物学的ホットスポット）を求め、各個体の集中利用場所に栄養段階で標準化した体組織の汚染物質濃度とストレスマーカー濃度をひも付けてハザード・リスクマップを作るものである。本年度は、新潟県粟島で、昨年度取りこぼした12個体と昨年度装着の100個体のうち、77個体を再捕獲し、ロガーを回収し体組織サンプリングし、再度ジオロケータを装着した。その結果、多くのサンプルにより、尾羽の水銀濃度は南シナ海越冬個体で高く、2006年から2010年より、オスの水銀濃度値は低いことがはっきりした。尾羽の窒素安定同位体比が高い個体は水銀濃度も高い傾向が見られ、生物増幅があることがわかったが、海域の海水中の窒素安定同位体比を反映するフェニルアラニンの窒素安定同位体比から、海域間でオオミズナギドリの栄養段階には差がないことが予想され、南シナ海越冬個体の水銀濃度が高いのは生物増幅のせいではなく、環境中の水銀濃度が高いためであると考えられた。尾羽のコルチコステロン濃度には海域間で差がなく、また水銀濃度とも関係がなく、尾羽の水銀濃度と繁殖成績との関係はあまり明瞭ではなかった。繁殖期には採食努力量の高い個体でストレス指標が高い傾向が一部見られた。さらに、尾脂腺ワックスのフッ素系界面活性剤（PFAS）分析法を開発し、その手法で調べたところ、南シナ海越冬個体でPFCAs濃度が高い傾向がありそうだった。また、データロガーをつけなかった個体からバイオプシーで採取した血液と羽の水銀の分析から、繁殖後に時期が進んでから生え変わる羽ほど水銀濃度が低く、血液の水銀濃度はその時生え変わっている羽の値と強い相関関係にあることから、個体の集中利用海域に尾羽の水銀濃度濃度をヒモ付けてマップ作成プロセスを補強する結果が得られた。
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), Hokkaido University, 19H01157
• TCA回路の多様性とその起源の解明
  科学研究費助成事業
  01 Apr. 2019 - 31 Mar. 2023
  布浦 拓郎; 力石 嘉人; 千葉 洋子
  本研究の目的は、生命誕生の鍵を握るTCA回路と還元的acetyl-CoA経路（WL経路）の多様性と進化を理解するため、主に始原的系統に属すアーキア、バクテリアにおける様々な不完全型TCA回路の仕組みを解明すると共に、生命進化におけるTCA回路とWL経路の関係性の解明を目指すことにある。
  TCA回路はエネルギー生産やアミノ酸・脂質等の生合成の基点となる根源的な代謝系であり、最も研究された代謝系の一つである。一方、ゲノム解析から非モデル微生物には不完全型等多様なTCA回路の存在が示唆され、実際、本研究グループがクエン酸合成酵素の可逆性を活かした可逆的TCA回路を始原的な水素酸化硫黄還元好熱細菌Thermosulfidibacterより見出した(Nunoura et al. 2018)ように、未だ重要な知見の発見が相次ぐ。本研究では、代表者らが独自に開発した微量メタボローム解析技術を駆使し、主に始原的な系統群における多様なTCA回路の生理的機能の解明を目指す。
  2020年度においては、Orbitrap Fusion 質量分析計による有機酸のアイソトポマー解析条件の検討を実施し、TCA回路に関連する有機酸については、超好熱性アーキア細胞からのメタボライト抽出からアイソトポマー解析に至る一連の解析フローをほぼ確立した。また、不完全型の還元的TCA回路の存在が示唆されてきた水素資化性好熱性メタン菌を対象としたOrbitrap Fusion MSを用いた炭素固定経路及び不完全型TCA回路の検証を進めた。更に、それぞれ独立栄養性及び従属栄養性超好熱アーキア株における炭素固定能及びTCA回路の役割に関する検討を実施した。
  日本学術振興会, 基盤研究(A), 国立研究開発法人海洋研究開発機構, 19H00988
• Understanding of biochemistry of chlorophyll c to shed light on evolution of marine primary production over the Phanerozoic Eon
  Grants-in-Aid for Scientific Research
  01 Apr. 2018 - 31 Mar. 2023
  柏山 祐一郎; 原田 二朗; 塚谷 祐介; 神川 龍馬; 力石 嘉人; 木下 雄介; 谷藤 吾朗; 伊庭 靖弘
  本研究では，①クロロフィルｃの生合成関連遺伝子・タンパク質の探索，②クロロフィル類の分解代謝経路に関わる遺伝子・タンパク質の探索，③クロロフィルｃを有する藻類およびその起源に関わる系統の真核生物の地質情報の研究の３つのアプローチを同時進行させてきた。②に関して，最古の真核藻類の出現時期の再検証の必要のため，カナダおよびアメリカの研究者とカナダの北極圏サマセット島への２年度にわたる共同調査の実施が計画されていたがＣｏｖｉｄ－１９パンデミックの影響により中止を余儀なくされ，今後についても確実な実施の目処が立たないのが現実である。
  この状況を受けて，研究の方向性を転換して，少なくとも今年度と来年度について，①と③の項目に集中することとした。すなわち，まず①に関しては，同様に未同定である二次植物のクロロフィルａ合成遺伝子の一部についても視野に入れて，網羅的に機能遺伝子の探索を進めた。ここでは，クロロフィルｃ合成系が二次植物にのみ見出される事実を重要視し，葉緑体獲得進化に伴う遺伝子重複により生じたクロロフィル合成関連遺伝子のパラログ候補を，全遺伝子情報が既に明らかとなっている有色および無職の珪藻類とクリプト藻類のデータベースから探索した。そして，有機合成した基質クロロフィル中間代謝産物を用いて in vitroでの酵素実験を実施し，いくつかの遺伝子について機能を特定した。これらについては，光合成バクテリアのクロロフィル合成関連遺伝子を欠損させた変異体群を作成したin vivo実験も展開している。③に関しては，分解代謝の研究のためのモデル生物として，これまでのPeranema trichophorumに加えて，珪藻捕食性の鞭毛虫Amastigomonada sp.についても，クロロフィル消化の有無でのトランスクリプトーム変化の解析を進めており，今度候補となる代謝遺伝子を探索していく。
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), Fukui University of Technology, 18H03743
• A new method for minimizing isotopic fractionation associated with derivatization of organic compounds
  Grants-in-Aid for Scientific Research
  28 Jun. 2019 - 31 Mar. 2021
  Chikaraishi Yoshito
  In this study, I developed a new method for minimizing isotopic fractionation associated with derivatization (particularly for acylation) of organic compounds. During acylation of amino acids, there is a significantly-large fractionation in 13C/12C, which is caused by preferential reaction of 12C on the acetyl reagents to amino acids. However, the isotopic fractionation can be reduced when amino acids are acylated with a surfactant and be diluted when the acyl group on the amino acids are replaced with that on the solvent.
  Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Research (Exploratory), Hokkaido University, 19K21888
• Presence and chirality of sugars formed in the early solar system: a new origin of biomolecule
  Grants-in-Aid for Scientific Research
  01 Apr. 2018 - 31 Mar. 2021
  Furukawa Yoshihiro
  Sugars are important constituents of life, but have never found in extraterrestrial samples and space. In this research we found extraterrestrial ribose and related sugars from meteorites and published the paper in PNAS. With laboratory experiments, the synthetic reaction of sugars was found to be formose-type reaction and this reaction was found to be a major synthetic reaction of meteorite organic compounds that provided large carbon isotope differences between amino acids and insoluble organic matter.
  We also succeeded in developing the protocol of chiral analysis of the sugars and investigated the chirality of meteorite sugars.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), Tohoku University, 18H03728
• Refinement of biomarker-based paleovegetation analysis, and its application to reconstruction of the paleovegetational variation in the northern Japan over the past 5 million years
  Grants-in-Aid for Scientific Research
  01 Apr. 2018 - 31 Mar. 2021
  Sawada Ken
  The objective of this study is to reconstruct variations in paleovegetation and terrestrial paleoenvironment by analyses of terrestrial plant-derived biomarkers and pollen/spore in sediment cores from Japan Sea off Hokkaido (U1422 and U1423 cores) collected by the International Ocean Drilling Program (IODP). We reconstructed the paleovegetation variations during ca. 4.3 million years and centurial-scale variations during ca. 700 kiloyears in U1423 and U1422 sites, respectively. The paleovegetation variations reconstructed by the coniferous diterpenoids and the triterpenoids derived by broad-leaved tree are synchronous to the global climatic variations such as warm/cool conditions with glacial/interglacial or centurial scales, elucidating paleoclimatic system variations related to monsoonal system in the northern Japan Sea by combined analyses of organic molecules and pollens.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 18H01322
• Development of a highly sensitive method for stable isotope analysis of amino acids
  Grants-in-Aid for Scientific Research
  01 Apr. 2017 - 31 Mar. 2021
  Chikaraishi Yoshito
  In this study, I developed a highly sensitive method for stable isotope analysis of amino acids, based on the incorporation of the following 4 techniques: (1) redesign of unions for connecting capillary column with reactors and traps; (2) increase of reactivity for reactors with metal catalyst; (3) installation of a multiple purpose sampler (MPS); and utilization of column coupling method. The results indicate that GC-IRMS modified in this study has a high sensitivity by approximately 100 times compared to the commercial GC-IRMS.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 17H02988
• Development of a methodology for measuring the energy transfer along food webs on aquatic-terrestrial mixed resources
  Grants-in-Aid for Scientific Research
  30 Jun. 2017 - 31 Mar. 2019
  Chikaraishi Yoshito; ISHIKAWA Naoto; SUGAYA Satoshi; TAKIZAWA Yuko; SASAKI Yoko; TAKANO Yoshinori; OGAWA Nanako; OHKOUCHI Naohiko; TSUCHIYA Masashi
  In this study, I developed ‘column-coupling method’ for measuring stable isotopic composition of methionine, a very minor but indispensable amino acid, in natural organisms. Moreover, applying this method developed, we established a compound-specific isotope methodology for estimating ‘resource proportion (aquatic X% vs. terrestrial Y%)’ and ‘trophic position’ of organisms in food webs where both phytoplankton and terrestrial-plants are potentially utilized as primary resources for consumer species along food chains.
  The results including the method and methodology were published as a paper in Limnology and oceanography: Methods, in 2018.
  Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Research (Exploratory), Hokkaido University, 17K18796
• A rapid derivatization method for measuring the stable isotope ratios of fatty acids in the study of biogeochemical cycles
  Grants-in-Aid for Scientific Research
  01 Apr. 2015 - 31 Mar. 2018
  GOTO Akiko; CHIKARAISHI Yoshito
  Stable isotope ratios (D/H, 13C/12C) analysis of fatty acids have been widely employed as a powerful tool for tracing biological sources and production/consumption processes of lipids in diverse studies. However, enough to benefit from this isotope analysis, we must reduce inconvenience in the derivatization method in the current procedure. In this study, we replace the standard acid-alcohol derivatization by the chloroformate derivatization, to much modify and reduce this inconvenience. Unlike the standard derivatization (which requires toxic reagents at high temperature for a few hours under hydrophobic condition), the chloroformate derivatization well work less-toxic reagents at room temperature for a few minutes. Moreover, this new derivatization does not strictly require hydrophobic condition (where water content by ~2% is permitted), resulting in that great care on the hydrophobicity is unnecessary for the derivatization, for example, even in rainy season.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Kanazawa University, 15K00519
• Biogeosciences of sediment-water interface: comprehensive understandings of ecosystem functioning, dynamics and material cycles at sediment-water interface
  Grants-in-Aid for Scientific Research
  01 Apr. 2013 - 31 Mar. 2017
  KITAZATO HIROSHI; Glud Ronnie N.; Karolina Koho
  We have investigated sediment-water interface dynamics through in-situ observations and laboratory experiments. Ecosystem Functions will be made clear through daily changes in chemocline. We have attempted to construct proxies that represent sediment-water interface dynamics. Optode observations, population dynamics, ecosystem functioning of benthic foraminifera were done during the project years. Foraminiferal test formation processes and quantitative analyses of trace elements in foraminiferal test and isotopic ecology have also carried out.
  We have made clear test formation processes of foraminifera in detail. Foraminiferal test certainly recorded variations of environments. Trace elements in foraminiferal tests should be related to changes in sediment-water interface. Changes in trace elements in foraminiferal test are related to that of biogeochemical cycles in global scales.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), 25247085
• Development of chiral-isomer specific isotope analysis of amino acids, for advances in studies for the interaction between life and organic compounds
  Grants-in-Aid for Scientific Research
  01 Apr. 2012 - 31 Mar. 2016
  Chikaraishi Yoshito
  In this study, I challenged the development of chiral-isomer specific isotope analysis of nitrogen, carbon, and hydrogen within amino acids. The results show that the isotope analysis of nitrogen and carbon is successfully achieved by using a combination of pivaloyl/isobuthyl ester derivatization with a polar GC column, resulting in a 1 sigma standard deviation being better than ± 0.5‰ based on the S/N ratio of >20 with baseline separation on the chromatogram. I also briefly confirmed that this method is widely applicable to biological (e.g., animal tissues), geological (e.g., sendiments), and extraterrestrial samples (meteorites). In contrast, the isotope analysis of hydrogen is still in the early-development stage, because I cannot control the considerable isotopic fractionation of hydrogen/deuterium on the amino group of amino acids during extraction and GC elution processes.
  Japan Society for the Promotion of Science, Grant-in-Aid for Young Scientists (A), Japan Agency for Marine-Earth Science and Technology, 24684041
• A search of novel surrogates of sterols in anaerobic eukaryotes
  Grants-in-Aid for Scientific Research
  01 Apr. 2013 - 31 Mar. 2015
  TAKISHITA Kiyotaka; OHKOUCHI Naohiko; CHIKARAISHI Yoshito
  It is known that sterols are associated with fluidity and permeability of eukaryotic cell membranes, and are key to fundamental eukaryotic-specific cellular processes such as phagocytosis. Several steps of de novo sterol biosynthesis require molecular oxygen. Our studies unveiled that some of eukaryotes inhabiting anoxic environments have neither sterols nor their structurally similar molecules based on analyses of genome, transcriptome, and GC-MS. However, it seems that the anaerobic eukaryotes in question can produce ceramides, in which a hydrophilic portion is very small compared with a hydrophobic portion as in the case of sterols, and the ceramides could be surrogates of sterols in these eukaryotes.
  Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Exploratory Research, Japan Agency for Marine-Earth Science and Technology, 25650132
• Symbiosis drove foraminiferal evolution
  Grants-in-Aid for Scientific Research
  01 Apr. 2012 - 31 Mar. 2015
  TSUCHIYA Masashi; FUJITA Kazuhiko; ISHIMURA Toyoho; CHIKARAISHI Yoshito; SAKAI Saburo; OGURI Kazumasa; TOYOFUKU Takashi; NOMAKI Hidetaka; YOSHIDA Takao; FREDERIC Sinniger
  Host-symbiont interactions are thought to be a key factor for adaptation and may be the driving force behind the evolution of endosymbiont-bearing foraminifers. We determined the kleptoplasts in a rocky-shore benthic foraminifer that originated from periphytic diatoms. Kleptoplasts were located near the host cell cortex, just under the pore plug, mainly along the dorsal side, which is important for oxygenic photosynthesis in light. The lifespan of kleptoplasts varied according to the intensity and duration of light irradiation and food availability. Host foraminifera metabolized food materials to maintain the activity of kleptoplasts and effectively utilized photosynthetic products from both organic and inorganic materials in response to the ambient environment. In fact, the trophic hierarchy according to the nitrogen isotopic composition of selected amino acids indicated that host foraminifers were primary producers as well as primary consumers in nature.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Japan Agency for Marine-Earth Science and Technology, 24340131
• Development of NMR application to Geo-metabolomics
  Grants-in-Aid for Scientific Research
  2010 - 2012
  CHIKARAISHI Yoshito
  As a NMR (Nuclear Magnetic Resonance) application to geochemistry, I tried to develop a rapid and simple primary screening method to identify and quantify organic compounds in extracts from geological samples (e.g., soils and sediments). The results show that 1H-MNR with 1 mm probe can be very much useful for a rapid and simple primary screening (both identification and quantification) of several targeted organic compounds such as chlorophylls and amino acids in the extracts from soils and lacustrine sediments. However, at this moment, it did not work sufficiently for extracts from marine sediments, because high concentration of organic acids and salts in these samples always obstruct spectrum-scan with high resolution. Moreover, other nuclear NMR such as <13>^C NMR and <15>^N NMR and two-dimensional NMR such as 1^H^<-13>C and 1^H^<-15>N were also not useful as a rapid and simple primary screening method for geological samples due to low sensitivity of the spectrum-scan.
  Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Exploratory Research, Japan Agency for Marine-Earth Science and Technology, 22654067
• Biotic history has accelerated under anoxic environments - Paradox of Foraminifera evolution can solve through field observation, laboratory culture and genomic analyses.
  Grants-in-Aid for Scientific Research
  2009 - 2012
  KITAZATO Hiroshi; TSUCHIYA Masashi; OGURI Kazumasa; TOYOFUKU Takashi; CHIKARAISHI Yoshito; NOMAKI Hidetaka
  We hypothesized that the evolution of marine protists might been enhanced by active microbial symbiosis. The symbiotic relationships with microbes were suitable to survive during the crisis when the anoxic environments were dominant in the ocean. The crisis is not really crisis for eukaryotic unicellular organisms because they may potentially positively adaptable to this anoxia by various types of symbiosis. We have tested the hypothesis through field surveys, accurate environment assessments, genomics, precise laboratory culture and biogeochemical measurement. Field studies were carried out at Sagami Bay, Shimoda Bay, Pacific Ocean (off Hachinohe), Namako-ike lake of Kamikoshiki-jima island, etc. The results are reported through 29 papers, 42 presentations and others for science community. Meanwhile, the knowledge has immediately transferred to society by Internet, seminars, press release and other occasions.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), Japan Agency for Marine-Earth Science and Technology, 21244079
• Development of multi-stable isotope analytical method of amino acids
  Grants-in-Aid for Scientific Research
  2009 - 2011
  CHIKARAISHI Yoshito
  I developed a compound-specific isotope method for measuring the stable nitrogen, carbon, and hydrogen isotopic compositions of amino acids. The results show(1) nitrogen isotopic composition can be determined by pivaloyl/isopropyl ester derivatization, with better than±0.5‰and the minimum sample amount of 0.5 nmol N,(2) carbon isotopic composition can be determined by ethyl ester derivatization, with better than±0.5‰and the minimum sample amount of 0.1 nmol N, and hydrogen isotopic composition can be determined by pivaloyl/isopropyl ester derivatization, with better than±50-100‰and the minimum sample amount of 0.5 nmol N. However, the carbon isotope analysis is only available for standard solution of amino acids but not for natural samples, at this moment.
  Japan Society for the Promotion of Science, Grant-in-Aid for Young Scientists (A), Japan Agency for Marine-Earth Science and Technology, 21684033
• Ecological roles of Xenophyophorean foraminifera in the deep-sea biological communities and early evolution of foraminifera
  Grants-in-Aid for Scientific Research
  2009 - 2011
  TSUCHIYA Masashi; TOYOFUKU Takashi; NOMAKI Hidetaka; CHIKARAISHI Yoshito
  The purpose of this study is to clarify ecological roles of xenophyophorean foraminifera in the deep-sea biological communities and early evolution of foraminifera, we carried out molecular phylogenetic analyses, ultrastructural observations and stable isotope analyses. The result of molecular phylogenetic analyses of nuclear ribosomal RNA indicates that Shinkaiya lindsayi, xenophyophore, indicates sister clade with other xenophyophore, Syringammina corbicula, shows monophyly relationships. We carried out in situ incubation experiments for two days at east off Torishima Is. at a depth of 5, 371 m. Xenophyophore rapidly fed both dissolved and particulate organic materials. Although limited food materials reached to the deep-sea floor in the oligotrophic region, xenophyophore have a potential for rapid growth, they indicate rapid uptake of food materials.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Japan Agency for Marine-Earth Science and Technology, 21540489
• Development of enantiomer-specific isotope analysis (ESIA) of amino acids
  Grants-in-Aid for Scientific Research
  2008 - 2009
  TAKANO Yoshinori; OHKOUCHI Naohiko; CHIKARAISHI Yoshito
  生体を構成する分子には、光学異性体や構造異性体が存在する。身近な光学異性体の例でいうと、タンパク質を構成するアミノ酸は、基本的にL-体アミノ酸から構成され、核酸の糖は、D-体リボースから構成されることが挙げられる。また、D-アラニンなどのようにタンパク質は構成しないが、細胞内のペプチドグリカンとして局所的に高濃度に存在する場合がある。これらの他にも生体内で生理活性を持つ種々の分子は、いずれかの異性体に偏っていることが多い。本研究では、従来のキラルなキャピラリーカラムを用いた光学異性体の分離ではなく、光学活性アルコール付加によるジアステレオマー誘導体化法を導入し、自然界に存在する光学異性体および構造異性体の個々の分子レベル窒素同位体比の評価を行った。
  Japan Society for the Promotion of Science, Grant-in-Aid for Young Scientists (B), Japan Agency for Marine-Earth Science and Technology, 20740316
• Reconstruction of marine nitrogen cycle by compound-specific stable nitrogen isotope analysis of orga nic compounds
  Grants-in-Aid for Scientific Research
  2007 - 2008
  CHIKARAISHI Yoshito
  堆積物や生物殻体(貝殻や骨)に含まれるアミノ酸・クロロフィルの安定窒素同位体比(15_N/14_N)は,過去の地球環境の窒素サイクルを知り得る唯一のツールとして期待されている。
  本研究では,海洋堆積岩(数千万年前)・海洋堆積物(数百万年前~現在)・生物化石(数万年~現在)・ホルマリン固定生物(数十年前~現在)・貝殻(数年前~現在)などの様々な試料に対し本解析法を適用し,本手法が様々なケースに広く利用可能であることを証明した。
  Japan Society for the Promotion of Science, Grant-in-Aid for Young Scientists (Start-up), Japan Agency for Marine-Earth Science and Technology, 19840054