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Seawater recirculation through subducting sediments sustains a deeply buried population of sulfate‐reducing bacteria
Author(s) -
Cox Toni L.,
Gan Han Ming,
Moreau John W.
Publication year - 2019
Publication title -
geobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.859
H-Index - 72
eISSN - 1472-4669
pISSN - 1472-4677
DOI - 10.1111/gbi.12324
Subject(s) - sulfate , seawater , geology , environmental chemistry , population , sulfate reducing bacteria , total organic carbon , microbial population biology , anaerobic oxidation of methane , oceanography , geochemistry , pyrite , hydrothermal vent , methane , ecology , chemistry , bacteria , hydrothermal circulation , paleontology , biology , demography , organic chemistry , sociology
Abstract Subseafloor sulfate concentrations typically decrease with depth as this electron acceptor is consumed by respiring microorganisms. However, studies show that seawater can flow through hydraulically conductive basalt to deliver sulfate upwards into deeply buried overlying sediments. Our previous work on IODP Site C0012A (Nankai Trough, Japan) revealed that recirculation of sulfate through the subducting Philippine Sea Plate stimulated microbial activity near the sediment–basement interface ( SBI ). Here, we describe the microbial ecology, phylogeny, and energetic requirements of population of aero‐tolerant sulfate‐reducing bacteria in the deep subseafloor. We identified dissimilatory sulfite reductase gene ( dsr ) sequences 93% related to oxygen‐tolerant Desulfovibrionales species across all reaction zones while no SRB were detected in drilling fluid control samples. Pore fluid chemistry revealed low concentrations of methane (<0.25 mM), while hydrogen levels were consistent with active bacterial sulfate reduction (0.51–1.52 nM). Solid phase total organic carbon ( TOC ) was also considerably low in these subseafloor sediments. Our results reveal the phylogenetic diversity, potential function, and physiological tolerance of a community of sulfate‐reducing bacteria living at ~480 m below subducting seafloor.