Michinari Sunamura

The University of Tokyo, Tōkyō, Japan

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Publications (35)69.61 Total impact

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    ABSTRACT: Hadal oceans at water depths below 6,000 m are the least-explored aquatic biosphere. The Challenger Deep, located in the western equatorial Pacific, with a water depth of ∼11 km, is the deepest ocean on Earth. Microbial communities associated with waters from the sea surface to the trench bottom (0 ∼10,257 m) in the Challenger Deep were analyzed, and unprecedented trench microbial communities were identified in the hadal waters (6,000 ∼10,257 m) that were distinct from the abyssal microbial communities. The potentially chemolithotrophic populations were less abundant in the hadal water than those in the upper abyssal waters. The emerging members of chemolithotrophic nitrifiers in the hadal water that likely adapt to the higher flux of electron donors were also different from those in the abyssal waters that adapt to the lower flux of electron donors. Species-level niche separation in most of the dominant taxa was also found between the hadal and abyssal microbial communities. Considering the geomorphology and the isolated hydrotopographical nature of the Mariana Trench, we hypothesized that the distinct hadal microbial ecosystem was driven by the endogenous recycling of organic matter in the hadal waters associated with the trench geomorphology.
    Proceedings of the National Academy of Sciences 02/2015; 112(11). DOI:10.1073/pnas.1421816112 · 9.67 Impact Factor
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    ABSTRACT: After the discovery of seafloor hydrothermal venting, it became evident that the subseafloor fluid advection system plays an extremely important role in the Earth’s element cycle. We designate these fluid advections as sub-seafloor TAIGAs (which stand for Trans-crustal Advection and In-situ biogeochemical processes of Global sub-seafloor Aquifers. In Japanese, “taiga” refers to “a great river”). This concept emphasizes dynamic signature of subseafloor hydrosphere, especially for a hydrothermal fluid circulation system that might support subseafloor microbial ecosystem. However, the link between the fluid advection and microbial activity has never been clearly demonstrated. We therefore hypothesized four types of sub-seafloor TAIGAs; hydrogen, methane, sulfur, and iron to investigate the relation. Each type of TAIGA is characterized by the most dominant reducing substance available for chemosynthesis. Our trans-disciplinary research between 2008 and 2012 indicates that the hypothesis is valid and the microbial activity within the flow of TAIGAs has strong linkage to chemical characteristics of each TAIGA; that is, the subseafloor TAIGA supplies four different kinds of electron donor for respective chemolithoautotroph ecosystem which is suitable for particular electron donor. It is also shown that the composition of dissolved chemical species in the subseafloor TAIGAs are substantially affected by the geological background of their flow path such as volcanism, surrounding host rocks and tectonic settings. Our research clearly indicates that the chemosynthetic sub-seafloor biosphere is controlled and supported by Earth’s endogenous flux of heat and mass beneath the seafloor.
    Subseafloor Biosphere Linked to Hydrothermal Systems, 01/2015: pages 3-10; , ISBN: 978-4-431-54864-5
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    ABSTRACT: The impacts of lithological structure and geothermal gradient on subseafloor microbial communities were investigated at a marginal site of the Iheya North hydrothermal field in the Mid-Okinawa Trough. Subsurface marine sediments composed of hemipelagic muds and volcaniclastic deposits were recovered through a depth of 151 m below the seafloor at Site C0017 during the Integrated Ocean Drilling Program Expedition 331. Microbial communities inferred from 16S rRNA gene clone sequencing in low-temperature hemipelagic sediments were mainly composed of members of Chloroflexi and Deep Sea Archaeal Group. In contrast, 16S rRNA gene sequences of Marine Group I Thaumarchaeota dominated the microbial phylotype communities in the coarse-grained pumiceous gravels interbedded between the hemipelagic sediments. Based on the physical properties of sediments such as temperature and permeability, the porewater chemistry and the microbial phylotype compositions, the shift in the physical properties of the sediments is suggested to induce a potential subseafloor recharging flow of oxygenated seawater in the permeable zone, leading to the generation of variable chemical environments and microbial communities in the subseafloor habitats. In addition, the deepest section of sediments under high-temperature conditions (∼90°C) harbored the sequences of an uncultivated archaeal lineage of Hot Water Crenarchaeotic Group IV that may be associated with the high-temperature hydrothermal fluid flow. These results indicate that the subseafloor microbial community compositions and functions at the marginal site of the hydrothermal field are highly affected by the complex fluid flow structure, such as recharging seawater and underlying hydrothermal fluids, coupled with the lithologic transition of sediments.
    Applied and Environmental Microbiology 07/2014; 80(19). DOI:10.1128/AEM.01741-14 · 3.67 Impact Factor
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    ABSTRACT: We developed a new multi-water-sampling system, ANEMONE-11, for autonomous underwater vehicle and remotely operated underwater vehicle exploration. Water samples are continuously collected by the ANEMONE-11 sampler by an in situ water pump at 40 mL/min and are sent to a selection valve unit that consists of 128 valves connected to 40 mL sampling bottles (50 cm in length). Each valve in the unit is selected and opened at preprogrammed intervals. We also discuss the results of observations at a hydrothermal area in the Okinawa Trough.
    Methods in Oceanography 01/2014; 8. DOI:10.1016/j.mio.2014.02.001
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    ABSTRACT: We studied the relationship between viral particle and microbial cell abundances in marine subsurface sediments from three geographically distinct locations in the continental margins (offshore of the Shimokita Peninsula of Japan, the Cascadia Margin off Oregon and the Gulf of Mexico), and found depth variations in viral abundances among these sites. Viruses in sediments obtained offshore the Shimokita and in the Cascadia Margin generally decreased with increasing depth, whereas those in sediments from the Gulf of Mexico were relatively constant throughout the investigated depths. In addition, the abundance ratios of viruses to microbial cells notably varied among the sites, ranging between 10(-3) and 10(1) . The subseafloor viral abundance offshore the Shimokita showed a positive relationship with the microbial cell abundance and the sediment porosity. In contrast, no statistically significant relationship was observed in the Cascadia Margin and the Gulf of Mexico sites, presumably due to the long-term preservation of viruses from enzymatic degradation within the low-porosity sediments. Our observations indicate that viral abundance in the marine subsurface sedimentary environment is regulated not only by in situ production but also by the balance of preservation and decay, which is associated with the regional sedimentation processes in the geological settings.
    FEMS Microbiology Ecology 12/2013; 88(1). DOI:10.1111/1574-6941.12269 · 3.57 Impact Factor
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    ABSTRACT: During the Integrated Ocean Drilling Program (IODP) Expedition 331 at the Iheya North hydrothermal system in the Mid-Okinawa Trough by the D/V Chikyu, we conducted microbiological contamination tests of the drilling and coring operations. The contamination from the drilling mud fluids was assessed using both perfluorocarbon tracers (PFT) and fluorescent microsphere beads. PFT infiltration was detected from the periphery of almost all whole round cores (WRCs). By contrast, fluorescent microspheres were not detected in hydrothermally active core samples, possibly due to thermal decomposition of the microspheres under high-temperature conditions. Microbial contamination from drilling mud fluids to the core interior subsamples was further characterized by molecular-based evaluation. The microbial 16S rRNA gene phylotype compositions in the drilling mud fluids were mainly composed of sequences of Beta- and Gammaproteobacteria, and Bacteroidetes and not archaeal sequences. The phylotypes that displayed more than 97% similarity to the sequences obtained from the drilling mud fluids were defined as possible contaminants in this study and were detected as minor components of the bacterial phylotype compositions in 13 of 37 core samples. The degree of microbiological contamination was consistent with that determined by the PFT and/or microsphere assessments. This study suggests a constructive approach for evaluation and eliminating microbial contamination during riser-less drilling and coring operations by the D/V Chikyu.
    Frontiers in Microbiology 11/2013; 4:327. DOI:10.3389/fmicb.2013.00327 · 3.99 Impact Factor
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    ABSTRACT: Sediment-hosting hydrothermal systems in the Okinawa Trough maintain a large amount of liquid, supercritical and hydrate phases of CO(2) in the seabed. The emission of CO(2) may critically impact the geochemical, geophysical and ecological characteristics of the deep-sea sedimentary environment. So far it remains unclear whether microbial communities that have been detected in such high-CO(2) and low-pH habitats are metabolically active, and if so, what the biogeochemical and ecological consequences for the environment are. In this study, RNA-based molecular approaches and radioactive tracer-based respiration rate assays were combined to study the density, diversity and metabolic activity of microbial communities in CO(2)-seep sediment at the Yonaguni Knoll IV hydrothermal field of the southern Okinawa Trough. In general, the number of microbes decreased sharply with increasing sediment depth and CO(2) concentration. Phylogenetic analyses of community structure using reverse-transcribed 16S ribosomal RNA showed that the active microbial community became less diverse with increasing sediment depth and CO(2) concentration, indicating that microbial activity and community structure are sensitive to CO(2) venting. Analyses of RNA-based pyrosequences and catalyzed reporter deposition-fluorescence in situ hybridization data revealed that members of the SEEP-SRB2 group within the Deltaproteobacteria and anaerobic methanotrophic archaea (ANME-2a and -2c) were confined to the top seafloor, and active archaea were not detected in deeper sediments (13-30 cm in depth) characterized by high CO(2). Measurement of the potential sulfate reduction rate at pH conditions of 3-9 with and without methane in the headspace indicated that acidophilic sulfate reduction possibly occurs in the presence of methane, even at very low pH of 3. These results suggest that some members of the anaerobic methanotrophs and sulfate reducers can adapt to the CO(2)-seep sedimentary environment; however, CO(2) and pH in the deep-sea sediment were found to severely impact the activity and structure of the microbial community.
    The ISME Journal 10/2012; 7(3). DOI:10.1038/ismej.2012.124 · 9.30 Impact Factor
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    ABSTRACT: In this study, we investigated the diversity and spatial distribution of anaerobic methanotrophic archaea (ANMEs) in sediments of a gas hydrate field off Joetsu in the Japan Sea. Distribution of ANMEs in sediments was identified by targeting the gene for methyl coenzyme M reductase alpha subunit (mcrA), a phylogenetically conserved gene that occurs uniquely in methanotrophic and methanogenic archaea, in addition to 16S rRNA genes. Quantitative PCR analyses of mcrA genes in 14 piston core samples suggested that members of ANME-1 group would dominate AOM communities in sulfate-depleted sediments, even below the sulfate-methane interface, while ANME-2 archaea would prefer to populate in shallower sediments containing comparatively higher sulfate concentrations. These results suggest that, although the potential electron acceptors in sulfate-depleted habitats remain elusive, the niche separation of ANME-1 and -2 may be controlled by in situ concentration of sulfate and the availability in sediments.
    Geomicrobiology 02/2011; 28(2):118-129. DOI:10.1080/01490451003709334 · 1.44 Impact Factor
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    ABSTRACT: Spatial distribution, diversity, and composition of bacterial communities within the shallow sub-seafloor at the deep-sea hydrothermal field of the Suiyo Seamount, Izu-Bonin Arc, Western Pacific Ocean, were investigated. Fluids were sampled from four boreholes in this area. Each borehole was located near or away from active vents, the distance ranging 2–40 m from active vents. In addition, fluids discharging from a natural vent and ambient seawater were sampled in this area. We extracted DNA from each sample, amplified bacterial 16S rRNA genes by PCR, cloned the PCR products and sequenced. The total number of clones analyzed was 348. Most of the detected phylotypes were affiliated with the phylum Proteobacteria, of which the detection frequency in each clone library ranged from 84.6% to 100%. The bacterial community diversity and composition were different between hydrothermal fluids and seawater, between fluids from the boreholes and the vent, and even among fluids from each borehole. The relative abundances of the phylotypes related to Thiomicrospira, Methylobacterium and Sphingomonas were significantly different among fluids from each borehole. The phylotypes related to Thiomicrospira and Alcanivorax were detected in all of the boreholes and vent samples. Our findings provide insights into bacterial communities in the shallow sub-seafloor environments at active deep-sea hydrothermal vent fields.
    Deep Sea Research Part I Oceanographic Research Papers 10/2009; 56(10):1844–1855. DOI:10.1016/j.dsr.2009.05.004 · 2.57 Impact Factor
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    ABSTRACT: 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.
    Environmental Microbiology 09/2009; 11(12):3210-22. DOI:10.1111/j.1462-2920.2009.02031.x · 6.20 Impact Factor
  • Geochmica et Cosmochimica Acta 06/2009;
  • 01/2009; 118(6):1021-1026. DOI:10.5026/jgeography.118.1021
  • Michinari SUNAMURA · Takuroh NOGUCHI · Hiroyuki YAMAMOTO · Kei OKAMURA
    01/2009; 118(6):1160-1173. DOI:10.5026/jgeography.118.1160
  • Hiromi WATANABE · Hiroyuki YAMAMOTO · Miho ASADA · Michinari SUNAMURA
    01/2009; 118(6). DOI:10.5026/jgeography.118.xxii
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    ABSTRACT: Since the discovery of rich microbial communities at and around seafloor hydrothermal sites, their extension towards the oceanic crust beneath the seafloor is of great interest not only for microbial physiology/ecology but also for a wide range of Earth and planetary sciences. How can the communities survive in such an extreme environment? What kinds of metabolism are in action? It is proposed that the sub-seafloor ecosystems are characterized by different kinds of chemosynthetic primary production (carbon fixation), all of which are supported by chemical energy supplied from the sub-seafloor aquifers. We designate the unseen aquifers as sub-seafloor TAIGAs (great rivers) which are responsible for a geochemical flux equivalent to or even larger than that of terrestrial river runoff (e.g. Wheat and Mottl, 2000). Besides, they are responsible for supplying nutrients to microbes beneath the seafloor. We hypothesize that there are four representative TAIGAs based on the chemical energy of compounds of sulfur, carbon (methane), iron, and hydrogen, all of which are supported by the TAIGAs. It is important to note that the sub-seafloor ecosystems are controlled extensively by or are mutually related to the types of TAIGA that flow at the site. The hypothesis can be tested through cooperative research among microbiologists, geochemists, geophysicists, and geologists.
    01/2009; 118(6):1027-1036. DOI:10.5026/jgeography.118.1027
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    ABSTRACT: The phylogenetic group termed OP5 was originally discovered in the Yellowstone National Park hot spring and proposed as an uncultured phylum; the group was afterwards analyzed by applying culture-independent approaches. Recently, a novel thermophilic chemoheterotrophic filamentous bacterium was obtained from a hot spring in Japan that was enriched through various isolation procedures. Phylogenetic analyses of the isolate have revealed that it is closely related to the OP5 phylum that has mainly been constructed with the environmental clones retrieved from thermophilic and mesophilic anaerobic environments. It appears that the lineage is independent at the phylum level in the domain Bacteria. Therefore, we designed a primer set for the 16S rRNA gene to specifically target the OP5 phylum and performed quantitative field analysis by using the real-time PCR method. Thus, the 16S rRNA gene of the OP5 phylum was detected in some hot-spring samples with the relative abundance ranging from 0.2% to 1.4% of the prokaryotic organisms detected. The physiology of the above-mentioned isolate and the related environmental clones indicated that they are scavengers contributing to the sulfur cycle in nature.
    Applied and Environmental Microbiology 10/2008; 74(20):6223-9. DOI:10.1128/AEM.01351-08 · 3.67 Impact Factor
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    ABSTRACT: Microbial communities in a shallow submarine hydrothermal system near Taketomi Island, Japan, were investigated using cultivation-based and molecular techniques. The main hydrothermal activity occurred in a craterlike basin (depth, approximately 23 m) on the coral reef seafloor. The vent fluid (maximum temperature, >52 degrees C) contained 175 microM H2S and gas bubbles mainly composed of CH4 (69%) and N2 (29%). A liquid serial dilution cultivation technique targeting a variety of metabolism types quantified each population in the vent fluid and in a white microbial mat located near the vent. The most abundant microorganisms cultivated from both the fluid and the mat were autotrophic sulfur oxidizers, including mesophilic Thiomicrospira spp. and thermophilic Sulfurivirga caldicuralii. Methane oxidizers were the second most abundant organisms in the fluid; one novel type I methanotroph exhibited optimum growth at 37 degrees C, and another novel type I methanotroph exhibited optimum growth at 45 degrees C. The number of hydrogen oxidizers cultivated only from the mat was less than the number of sulfur and methane oxidizers, although a novel mesophilic hydrogen-oxidizing member of the Epsilonproteobacteria was isolated. Various mesophilic to hyperthermophilic heterotrophs, including sulfate-reducing Desulfovibrio spp., iron-reducing Deferribacter sp., and sulfur-reducing Thermococcus spp., were also cultivated. Culture-independent 16S rRNA gene clone analysis of the vent fluid and mat revealed highly diverse archaeal communities. In the bacterial community, S. caldicuralii was identified as the predominant phylotype in the fluid (clonal frequency, 25%). Both bacterial clone libraries indicated that there were bacterial communities involved in sulfur, hydrogen, and methane oxidation and sulfate reduction. Our results indicate that there are unique microbial communities that are sustained by active chemosynthetic primary production rather than by photosynthetic production in a shallow hydrothermal system where sunlight is abundant.
    Applied and Environmental Microbiology 12/2007; 73(23):7642-56. DOI:10.1128/AEM.01258-07 · 3.67 Impact Factor
  • Kota Kitazawa · Tatsuo Oji · Michinari Sunamura
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    ABSTRACT: Crinoids have been diverse organisms in marine epifaunal filter feeding communities at any level of tiering above the substrate since they appeared in the Ordovician. Feeding is regarded as the most important factor in producing the crinoid tiering, which is primarily defined by stalk length. The gut contents of five sympatric crinoid species (three isocrines and two comatulids) were observed, and these were compared with the stalk length and the fan density. We have classified these crinoid species into four groups based on the stalk length and fan density, e.g., long stalk with low fan density, long stalk with high fan density, short stalk with low fan density, and short stalk with high fan density. In the gut contents, diatom crusts were found mainly from species with longer stalks, and chlorophyll-like fluorescent material were only detected from the groups with a shorter or no stalk. The group with lower fan density contained more inorganic particles than the group with higher fan density. Therefore, the gut contents and their amounts depend on their stalk lengths and their fan densities. The results imply that diversified morphologies in the crinoids have evolved through adaptations to different ecological factors such as difference in their diets.
    Marine Biology 08/2007; 152(4):959-968. DOI:10.1007/s00227-007-0746-5 · 2.39 Impact Factor

Publication Stats

397 Citations
69.61 Total Impact Points


  • 2004–2015
    • The University of Tokyo
      • Department of Earth and Planetary Science
      Tōkyō, Japan
  • 2008
    • Kyushu University
      • Faculty of Sciences
      Hukuoka, Fukuoka, Japan
  • 2007
    • University of the Ryukyus
      • Graduate School of Engineering and Science
      Okinawa, Okinawa, Japan
  • 2003–2006
    • National Institute of Advanced Industrial Science and Technology
      Tsukuba, Ibaraki, Japan