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Tomohiro Toki

Bio: Tomohiro Toki is an academic researcher from University of the Ryukyus. The author has contributed to research in topics: Hydrothermal circulation & Accretionary wedge. The author has an hindex of 24, co-authored 62 publications receiving 1916 citations. Previous affiliations of Tomohiro Toki include University of Tokyo & Hokkaido University.


Papers
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Journal ArticleDOI
TL;DR: Under conventional growth conditions, the isotope fractionation of methanogenesis by M. kandleri strain 116 was similar to values previously reported for other hydrogenotrophic methanogens, but under high hydrostatic pressures, the atom fractionation effect became much smaller, and the kinetic isotope effect was one of the smallest effects ever reported.
Abstract: We have developed a technique for cultivation of chemolithoautotrophs under high hydrostatic pressures that is successfully applicable to various types of deep-sea chemolithoautotrophs, including methanogens. It is based on a glass-syringe-sealing liquid medium and gas mixture used in conjunction with a butyl rubber piston and a metallic needle stuck into butyl rubber. By using this technique, growth, survival, and methane production of a newly isolated, hyperthermophilic methanogen Methanopyrus kandleri strain 116 are characterized under high temperatures and hydrostatic pressures. Elevated hydrostatic pressures extend the temperature maximum for possible cell proliferation from 116°C at 0.4 MPa to 122°C at 20 MPa, providing the potential for growth even at 122°C under an in situ high pressure. In addition, piezophilic growth significantly affected stable carbon isotope fractionation of methanogenesis from CO2. Under conventional growth conditions, the isotope fractionation of methanogenesis by M. kandleri strain 116 was similar to values (−34‰ to−27‰) previously reported for other hydrogenotrophic methanogens. However, under high hydrostatic pressures, the isotope fractionation effect became much smaller (<−12‰), and the kinetic isotope effect at 122°C and 40 MPa was −9.4‰, which is one of the smallest effects ever reported. This observation will shed light on the sources and production mechanisms of deep-sea methane.

684 citations

Journal ArticleDOI
TL;DR: In this paper, the Global Edge Institute, Tokyo Institute of Technology, G1-25, Nagatsuta, Midori-ku, Yokohama 226-8502, Japan 8 Department of Environmental Science and Technology (DES) at Tokyo Institute for Advanced Research (TOAR), Tokyo, 1-15-1, Minamidai, Nakano-ku 2-15 Natsushima-cho, Yokosuka 237-0061, Tokyo 164-8639, Japan 3 Department of Earth Science, Gakushuin University, Nejiro 1-
Abstract: 1Ocean Research Institute (ORI), The University of Tokyo, 1-15-1, Minamidai, Nakano-ku, Tokyo 164-8639, Japan 2Precambrian Ecosystem Laboratory (PEL), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka 237-0061, Japan 3Department of Earth Science, Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka, Kita, Okayama, Okayama 700-8530, Japan 4Faculty of Sciences, Kyushu University, 6-10-1, Hakozaki, Higashi, Fukuoka 812-8581, Japan 5Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan 6Faculty of Science, Gakushuin University, Nejiro 1-5-1, Toshima-ku, Tokyo 171-8588, Japan 7Global Edge Institute, Tokyo Institute of Technology, G1-25, Nagatsuta, Midori-ku, Yokohama 226-8502, Japan 8Department of Environmental Science and Technology, Tokyo Institute of Technology, G1-25, Nagatsuta, Midori-ku, Yokohama 226-8502, Japan 9Subsurface Geobiology Advanced Research (SUGAR) Project, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka 237-0061, Japan 10Faculty of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho, Hakodate 041-8611, Japan

113 citations

Journal ArticleDOI
TL;DR: The Kairei and Edmond hydrothermal fields in the Indian Ocean are separated by 160 km, but exhibit distinct fluid chemistry: kairei fluids are hydrogen-rich; Edmond fluids are pure hydrogen-poor as discussed by the authors, which suggests that lithology controlled generation of hydrogen may have operated for a long time and is relevant to the origin of life on Earth.
Abstract: Hydrogen-rich hydrothermal areas, such as those in the Indian Ocean, may have had an influence on early evolution of life on Earth and thus have attracted interest because they may be a proxy for ancient ecosystems. The Kairei and Edmond hydrothermal fields in the Indian Ocean are separated by 160 km, but exhibit distinct fluid chemistry: Kairei fluids are hydrogen-rich; Edmond fluids are hydrogen-poor. At this region, the Central Indian Ridge shows an intermediate spreading rate, 48 mm year−1 as full rate, where the hydrothemal fields occur. Kairei field vent fluids show persistently high concentrations of H2. The Kairei field seems to be unique among hydrogen-enriched hydrothermal regions: most similar hydrogen-rich hydrothermal activity occurs along slowly spreading ridge, <40 mm year−1. The geological and tectonic aspects of the Kairei and Edmond hydrothermal fields were studied to try to elucidate geological constraints on hydrogen production. Visual observations of the seafloor near Kairei from a submersible revealed olivine-rich plutonic rocks with olivine gabbro-troctolite-dunite assemblages exposed within 15 km of the vent field, with serpentinized ultramafic mantle rocks on the Oceanic Core Complex (OCC). The OCC area might be a recharge zone of Kairei hydrothermal activity producing H2-rich vent fluids. The chaotic seafloor within 30 km of the Kairei field reflects a magma-starved condition persisting there for 1 Myr. Asymmetric geomagnetic and gravity anomalies near the Kairei field can be used to infer that patchy olivine-rich intrusions are scattered within mantle ultramafics, where infiltrated seawater reacts with magma and ultramafic rocks or olivine-rich rocks. The heterogeneous uppermost lithosphere containing shallow olivine-rich rock facies surrounding the Kairei field provides abundant H2 into the vent fluid through serpentinization. The hydrogen-rich Kairei field is hosted by basalt, with mafic-ultramafic olivine-rich lithology; the ordinary, hydrogen-poor Edmond field is hosted by a normal basaltic lithology. The contrasting geochemical signatures of the two fields reported here can also be found in ancient rocks from a juvenile Earth. This suggests that lithology-controlled generation of hydrogen may have operated for a long time and be relevant to the origin of life on Earth.

108 citations

Journal ArticleDOI
TL;DR: In this paper, the abundance, diversity and composition of microbial communities in crustal fluids at back-arc hydrothermal fields of the Southern Mariana Trough (SMT) were investigated using culture-independent molecular techniques based on 16S rRNA gene sequences.
Abstract: Summary To extend knowledge of subseafloor microbial communities within the oceanic crust, the abundance, diversity and composition of microbial communities in crustal fluids at back-arc hydrothermal fields of the Southern Mariana Trough (SMT) were investigated using culture-independent molecular techniques based on 16S rRNA gene sequences. Seafloor drilling was carried out at two hydrothermal fields, on- and off-ridge of the back-arc spreading centre of the SMT. 16S rRNA gene clone libraries for bacterial and archaeal communities were constructed from the fluid samples collected from the boreholes. Phylotypes related to Thiomicrospira in the Gammaproteobacteria (putative sulfide-oxidizers) and Mariprofundus in the Zetaproteobacteria (putative iron-oxidizers) were recovered from the fluid samples. A number of unique archaeal phylotypes were also recovered. Fluorescence in situ hybridization (FISH) analysis indicated the presence of active bacterial and archaeal populations in the fluids. The Zetaproteobacteria accounted for up to 32% of the total prokaryotic cell number as shown by FISH analysis using a specific probe designed in this study. Our results lead to the hypothesis that the Zetaproteobacteria play a role in iron oxidation within the oceanic crust.

80 citations

01 Jan 2009
TL;DR: The results lead to the hypothesis that the Zetaproteobacteria play a role in iron oxidation within the oceanic crust.
Abstract: Summary To extend knowledge of subseafloor microbial com- munities within the oceanic crust, the abundance, diversity and composition of microbial communities in crustal fluids at back-arc hydrothermal fields of the Southern Mariana Trough (SMT) were investigated using culture-independent molecular techniques based on 16S rRNA gene sequences. Seafloor drilling was carried out at two hydrothermal fields, on- and off-ridge of the back-arc spreading centre of the SMT. 16S rRNA gene clone libraries for bacterial and archaeal communities were constructed from the fluid samples collected from the boreholes. Phylotypes related toThiomicrospira in theGammaproteobacteria (putative sulfide-oxidizers) and Mariprofundus in the Zetaproteobacteria (putative iron-oxidizers) were recovered from the fluid samples. A number of unique archaeal phylotypes were also recovered. Fluores- cence in situ hybridization (FISH) analysis indicated the presence of active bacterial and archaeal popula- tions in the fluids. The Zetaproteobacteria accounted for up to 32% of the total prokaryotic cell number as shown by FISH analysis using a specific probe designed in this study. Our results lead to the hypoth- esis that the Zetaproteobacteria play a role in iron oxidation within the oceanic crust.

76 citations


Cited by
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01 Aug 2000
TL;DR: Assessment of medical technology in the context of commercialization with Bioentrepreneur course, which addresses many issues unique to biomedical products.
Abstract: BIOE 402. Medical Technology Assessment. 2 or 3 hours. Bioentrepreneur course. Assessment of medical technology in the context of commercialization. Objectives, competition, market share, funding, pricing, manufacturing, growth, and intellectual property; many issues unique to biomedical products. Course Information: 2 undergraduate hours. 3 graduate hours. Prerequisite(s): Junior standing or above and consent of the instructor.

4,833 citations

Journal Article
TL;DR: In this article, the authors present a document, redatto, voted and pubblicato by the Ipcc -Comitato intergovernativo sui cambiamenti climatici - illustra la sintesi delle ricerche svolte su questo tema rilevante.
Abstract: Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

4,187 citations

Journal ArticleDOI
TL;DR: This work shows that total microbial cell abundance in subseafloor sediment varies between sites by ca.
Abstract: The global geographic distribution of subseafloor sedimentary microbes and the cause(s) of that distribution are largely unexplored. Here, we show that total microbial cell abundance in subseafloor sediment varies between sites by ca. five orders of magnitude. This variation is strongly correlated with mean sedimentation rate and distance from land. Based on these correlations, we estimate global subseafloor sedimentary microbial abundance to be 2.9⋅1029 cells [corresponding to 4.1 petagram (Pg) C and ∼0.6% of Earth’s total living biomass]. This estimate of subseafloor sedimentary microbial abundance is roughly equal to previous estimates of total microbial abundance in seawater and total microbial abundance in soil. It is much lower than previous estimates of subseafloor sedimentary microbial abundance. In consequence, we estimate Earth’s total number of microbes and total living biomass to be, respectively, 50–78% and 10–45% lower than previous estimates.

791 citations

Journal ArticleDOI
TL;DR: Autonomous Underwater Vehicles (AUVs) have a wide range of applications in marine geoscience, and are increasingly being used in the scientific, military, commercial, and policy sectors as mentioned in this paper.

684 citations

Journal ArticleDOI
TL;DR: Genomic and metagenomic data predict a number of ecologically relevant capabilities for some acidobacteria, including the ability to: respond to soil macro-, micro nutrients and soil acidity, express multiple active transporters, degrade gellan gum and produce exopolysaccharide (EPS).
Abstract: The phylum Acidobacteria is one of the most widespread and abundant on the planet, yet remarkably our knowledge of the role of these diverse organisms in the functioning of terrestrial ecosystems remains surprisingly rudimentary. This blatant knowledge gap stems to a large degree from the difficulties associated with the cultivation of these bacteria by classical means. Given the phylogenetic breadth of the Acidobacteria, which is similar to the metabolically diverse Proteobacteria, it is clear that detailed and functional descriptions of acidobacterial assemblages are necessary. Fortunately, recent advances are providing a glimpse into the ecology of members of the phylum Acidobacteria. These include novel cultivation and enrichment strategies, genomic characterization and analyses of metagenomic DNA from environmental samples. Here, we couple the data from these complementary approaches for a better understanding of their role in the environment, thereby providing some initial insights into the ecology of this important phylum. All cultured acidobacterial type species are heterotrophic, and members of subdivisions 1, 3, and 4 appear to be more versatile in carbohydrate utilization. Genomic and metagenomic data predict a number of ecologically relevant capabilities for some acidobacteria, including the ability to: use of nitrite as N source, respond to soil macro-, micro nutrients and soil acidity, express multiple active transporters, degrade gellan gum and produce exopolysaccharide (EPS). Although these predicted properties allude to a competitive life style in soil, only very few of these prediction shave been confirmed via physiological studies. The increased availability of genomic and physiological information, coupled to distribution data in field surveys and experiments, should direct future progress in unraveling the ecology of this important but still enigmatic phylum.

629 citations