title: Changes in microbial communities associated with gas hydrates in subseafloor sediments from the Nankai Trough.
abstract: Little is known about the microbial distribution patterns in subseafloor sediments. This study examines microbial diversity and activities in sediments of the Nankai Trough, where biogenic gas hydrates are deposited. Illumina sequencing of 16S rRNA genes revealed that the prokaryotic community structure is correlated with hydrate occurrence and depth but not with the sedimentary facies. The bacterial phyla 'Atribacteria' lineage JS1 and Chloroflexi dominated in all samples, whereas lower taxonomic units of Chloroflexi accounted for community variation related to hydrate saturation. In archaeal communities, 'Bathyarchaeota' was significantly abundant in the hydrate-containing samples, whereas Marine Benthic Group-B dominated in the upper sediments without hydrates. mcrA gene sequences assigned to deeply branching groups and ANME-1 were detected only in hydrate-containing samples. A predominance of hydrogenotrophic methanogens, Methanomicrobiales and Methanobacteriales, over acetoclastic methanogens was found throughout the depth. Incubation tests on hydrate-containing samples with a stable isotope tracer showed anaerobic methane oxidation activities under both low- and seawater-like salinity conditions. These results indicate that the distribution patterns of microorganisms involved in carbon cycling changed with gas hydrate occurrence, possibly because of the previous hydrate dissociation followed by pore water salinity decrease in situ, as previously proposed by a geochemical study at the study site.
authors.affiliation: Institute for Geo-Resources and Environment, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Japan.
authors.forename: Taiki
authors.initials: T
authors.lastname: Katayama
authors.affiliation: Institute for Geo-Resources and Environment, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Japan hi-yoshioka@aist.go.jp.
authors.forename: Hideyoshi
authors.initials: H
authors.lastname: Yoshioka
authors.affiliation: Institute of Earthquake and Volcano Geology, Geological Survey of Japan, AIST, 1-1-1 Higashi, Tsukuba, Japan.
authors.forename: Hiroshi A
authors.initials: HA
authors.lastname: Takahashi
authors.affiliation: Technology and Research Center, Japan Oil, Gas and Metals National Corporation, 1-1-2 Hamada, Mihama-ku, Chiba, Japan.
authors.forename: Miki
authors.initials: M
authors.lastname: Amo
authors.affiliation: Technology and Research Center, Japan Oil, Gas and Metals National Corporation, 1-1-2 Hamada, Mihama-ku, Chiba, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Fujii
authors.affiliation: Institute for Geo-Resources and Environment, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Japan.
authors.forename: Susumu
authors.initials: S
authors.lastname: Sakata
mesh_terms: D001105:Archaea / Q000235:genetics; D001419:Bacteria / Q000235:genetics; D019605:Euryarchaeota / Q000235:genetics; D019015:Geologic Sediments / Q000382:microbiology*; D008697:Methane; D017012:Methanobacteriales / Q000235:genetics; D017018:Methanomicrobiales / Q000235:genetics; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012623:Seawater / Q000382:microbiology*; D014871:Water Microbiology
chemical_list: D012336:RNA, Ribosomal, 16S; D008697:Methane
keywords: 16S rRNA gene; Illumina sequencing; biogenic gas hydrate; deep biosphere; mcrA gene; subseafloor sediment