伊豆・小笠原カルデラ内熱水活動域における微生物の分布様式と多様性解析

PS63ポスター要旨 / ブルーアース2008（2008年3月13日～14日, 横浜市立大学金沢八景キャンパス）http://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt06-21_leg1/

Distribution and Niche Separation of Planktonic Microbial Communities in the Water Columns from the Surface to the Hadal Waters of the Japan Trench under the Eutrophic Ocean

The Japan Trench is located under the eutrophic Northwestern Pacific while the Mariana Trench that harbors the unique hadal planktonic biosphere is located under the oligotrophic Pacific. Water samples from the sea surface to just above the seafloor at a total of 11 stations including a trench axis station, were investigated several months after the Tohoku Earthquake in March 2011. High turbidity zones in deep waters were observed at most of the sampling stations. The small subunit (SSU) rRNA gene community structures in the hadal waters (water depths below 6000 m) at the trench axis station were distinct from those in the overlying meso-, bathy and abyssopelagic waters (water depths between 200 and 1000 m, 1000 and 4000 m and 4000 and 6000 m, respectively), although the SSU rRNA gene sequences suggested that potential heterotrophic bacteria dominated in all of the waters. Potential niche separation of nitrifiers, including ammonia-oxidizing archaea (AOA), was revealed by quantitative PCR analyses. It seems likely that Nitrosopumilus-like AOAs respond to a high flux of electron donors and dominate in several zones of water columns including shallow and very deep waters. This study highlights the effects of suspended organic matter, as induced by seafloor deformation, on microbial communities in deep waters and confirm the occurrence of the distinctive hadal biosphere in global trench environments hypothesized in the previous study.http://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr11-03/ehttp://www.godac.jamstec.go.jp/darwin/cruise/yokosuka/yk11-e03/ehttp://www.godac.jamstec.go.jp/darwin/cruise/yokosuka/yk11-e04_leg2/

Metabolically active microbial communities in marine sediment under high-CO2 and low-pH extremes

Sediment-hosting hydrothermal systems in the Okinawa Trough maintain a large amount of liquid, supercritical and hydrate phases of CO2 in the seabed. The emission of CO2 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-CO2 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 CO2-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 CO2 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 CO2 concentration, indicating that microbial activity and community structure are sensitive to CO2 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 CO2. 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 CO2-seep sedimentary environment; however, CO2 and pH in the deep-sea sediment were found to severely impact the activity and structure of the microbial community

各地の深海底に存在する褐色変色域での微生物調査

BE11-P72ポスター要旨 / ブルーアース2011（2011年3月7日～8日, 東京海洋大学品川キャンパス）http://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt05-18/ehttp://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt10-06_leg2/ehttp://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt10-13_leg2/ehttp://www.godac.jamstec.go.jp/darwin/cruise/yokosuka/yk10-10/

Two Bacteria Phylotypes Are Predominant in the Suiyo Seamount Hydrothermal Plume

Microbial diversity and populations in a hydrothermal plume that was present inside the caldera of the Suiyo Seamount, a submarine volcano on the Izu-Bonin Arc, were investigated by performing a phylogenetic analysis of the 16S rRNA gene and by using fluorescence in situ hybridization (FISH). Corresponding to transmissivity, an indicator of turbidity, the vertical total cell count as determined by 4′,6′-diamidino-2-phenylindole (DAPI) staining varied from 5.6 × 10(4) to 1.1 × 10(5) cells ml(−1), and the apparent plume layer was assessed to be at a depth of 1,050 to 1,200 m inside the caldera and to contain 1.0 × 10(5) to 1.1 × 10(5) cells ml(−1). From microbial samples collected in the plume by an in situ filtration system, the following two major phylogenetic groups, which were closely related to sulfur-oxidizing microbes, were obtained: the SUP05 group belonging to the gamma subclass of the Proteobacteria (13 of 20 clones) and the SUP01 group belonging to the epsilon subclass of the Proteobacteria (5 of 20 clones). Specific oligonucleotide probes for these groups (SUP05-187 and SUP01-63) were designed and were used with various water samples obtained from the Suiyo Seamount. In the apparent plume layer, up to 66% of the total counts of microbial cells were estimated to be Bacteria cells that hybridized to EUB338, and few cells were identified by the archaeal probe ARCH915. Almost all Bacteria cells were hard to identify with the known group-specific probes, such as ALF19, GAM42a, and CF319, while 88 to 90% of the Bacteria cells hybridized with SUP05-187 and >98% of them were considered members of the SUP05 and SUP01 populations. In a low-temperature vent fluid emitted from a bivalve-colonized mound, the SUP05 cells accounted for >99% of the Bacteria cells, suggesting that a portion of the plume cells originated on the surface of the seafloor at a depth of about 1,380 m. From further analysis of cell morphology (i.e., cell size and cell elongation index) we inferred that the SUP05 cells were active in the plume layer at a depth of 1,050 to 1,200 m compared to the activity in a near-bottom layer, while many elongated cells were found between these layers. These findings suggest that the morphology and distribution of SUP05 cells have complex relationships with hydrothermal activities and water circulation. Although growth and production rates remain to be defined, we concluded that this Suiyo Seamount caldera has functioned as a natural continuous incubator for these two phylotypes of Bacteria in an aphotic deep-sea environment