title: Defining boundaries for the distribution of microbial communities beneath the sediment-buried, hydrothermally active seafloor.
abstract: Subseafloor microbes beneath active hydrothermal vents are thought to live near the upper temperature limit for life on Earth. We drilled and cored the Iheya North hydrothermal field in the Mid-Okinawa Trough, and examined the phylogenetic compositions and the products of metabolic functions of sub-vent microbial communities. We detected microbial cells, metabolic activities and molecular signatures only in the shallow sediments down to 15.8 m below the seafloor at a moderately distant drilling site from the active hydrothermal vents (450 m). At the drilling site, the profiles of methane and sulfate concentrations and the δ13C and δD isotopic compositions of methane suggested the laterally flowing hydrothermal fluids and the in situ microbial anaerobic methane oxidation. In situ measurements during the drilling constrain the current bottom temperature of the microbially habitable zone to ~45 °C. However, in the past, higher temperatures of 106-198 °C were possible at the depth, as estimated from geochemical thermometry on hydrothermally altered clay minerals. The 16S rRNA gene phylotypes found in the deepest habitable zone are related to those of thermophiles, although sequences typical of known hyperthermophilic microbes were absent from the entire core. Overall our results shed new light on the distribution and composition of the boundary microbial community close to the high-temperature limit for habitability in the subseafloor environment of a hydrothermal field.
authors.affiliation: Department of Subsurface Geobiological Analysis and Research (D-SUGAR), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan.|Department of Earth and Planetary Science, University of Tokyo, Tokyo, Japan.|Faculty of Social and Cultural Studies, Kyushu University, Fukuoka, Japan.
authors.forename: Katsunori
authors.initials: K
authors.lastname: Yanagawa
authors.affiliation: Geomicrobiology Group, Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Kochi, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Ijiri
authors.affiliation: Geomicrobiology, Federal Institute for Geosciences and Natural Resources (BGR), Hannover, Germany.
authors.forename: Anja
authors.initials: A
authors.lastname: Breuker
authors.affiliation: Department of Subsurface Geobiological Analysis and Research (D-SUGAR), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan.
authors.forename: Sanae
authors.initials: S
authors.lastname: Sakai
authors.affiliation: Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University, Higashi-ku, Fukuoka, Japan.
authors.forename: Youko
authors.initials: Y
authors.lastname: Miyoshi
authors.affiliation: Department of Subsurface Geobiological Analysis and Research (D-SUGAR), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan.
authors.forename: Shinsuke
authors.identifier: 0000-0002-7807-024X
authors.initials: S
authors.lastname: Kawagucci
authors.affiliation: Interdisciplinary Science Unit, Multidisciplinary Science Cluster, Research and Education Faculty, Kochi University, Kochi, Japan.
authors.forename: Takuroh
authors.initials: T
authors.lastname: Noguchi
authors.affiliation: Marine Functional Biology Group, Research and Development Center for Marine Biosciences, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan.
authors.forename: Miho
authors.initials: M
authors.lastname: Hirai
authors.affiliation: Geomicrobiology, Federal Institute for Geosciences and Natural Resources (BGR), Hannover, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Schippers
authors.affiliation: Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University, Higashi-ku, Fukuoka, Japan.
authors.forename: Jun-Ichiro
authors.initials: JI
authors.lastname: Ishibashi
authors.affiliation: Department of Subsurface Geobiological Analysis and Research (D-SUGAR), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Takaki
authors.affiliation: Department of Earth and Planetary Science, University of Tokyo, Tokyo, Japan.
authors.forename: Michinari
authors.initials: M
authors.lastname: Sunamura
authors.affiliation: Department of Earth and Planetary Science, University of Tokyo, Tokyo, Japan.
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Urabe
authors.affiliation: Marine Functional Biology Group, Research and Development Center for Marine Biosciences, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan.
authors.forename: Takuro
authors.initials: T
authors.lastname: Nunoura
authors.affiliation: Department of Subsurface Geobiological Analysis and Research (D-SUGAR), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Takai
mesh_terms: D001105:Archaea / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D001419:Bacteria / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D019641:DNA, Archaeal / Q000737:chemistry / Q000235:genetics; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004777:Environment; D019015:Geologic Sediments / Q000737:chemistry / Q000382:microbiology*; D006358:Hot Temperature; D060086:Hydrothermal Vents / Q000382:microbiology*; D008697:Methane / Q000032:analysis; D059013:Microbial Consortia; D009792:Oceans and Seas; D010802:Phylogeny; D012335:RNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D012623:Seawater / Q000382:microbiology; D017422:Sequence Analysis, DNA; D013431:Sulfates / Q000032:analysis
chemical_list: D019641:DNA, Archaeal; D004269:DNA, Bacterial; D012335:RNA, Ribosomal; D013431:Sulfates; D008697:Methane