title: Hydrogen Utilization Potential in Subsurface Sediments.
abstract: Subsurface microbial communities undertake many terminal electron-accepting processes, often simultaneously. Using a tritium-based assay, we measured the potential hydrogen oxidation catalyzed by hydrogenase enzymes in several subsurface sedimentary environments (Lake Van, Barents Sea, Equatorial Pacific, and Gulf of Mexico) with different predominant electron-acceptors. Hydrogenases constitute a diverse family of enzymes expressed by microorganisms that utilize molecular hydrogen as a metabolic substrate, product, or intermediate. The assay reveals the potential for utilizing molecular hydrogen and allows qualitative detection of microbial activity irrespective of the predominant electron-accepting process. Because the method only requires samples frozen immediately after recovery, the assay can be used for identifying microbial activity in subsurface ecosystems without the need to preserve live material. We measured potential hydrogen oxidation rates in all samples from multiple depths at several sites that collectively span a wide range of environmental conditions and biogeochemical zones. Potential activity normalized to total cell abundance ranges over five orders of magnitude and varies, dependent upon the predominant terminal electron acceptor. Lowest per-cell potential rates characterize the zone of nitrate reduction and highest per-cell potential rates occur in the methanogenic zone. Possible reasons for this relationship to predominant electron acceptor include (i) increasing importance of fermentation in successively deeper biogeochemical zones and (ii) adaptation of H2ases to successively higher concentrations of H2 in successively deeper zones.
authors: MARUM - Center for Marine Environmental Sciences, University of BremenBremen, Germany; Geomicrobiology Group, Institute of Earth and Environmental Science, University of PotsdamPotsdam, Germany.
authors: Rishi R
authors: RR
authors: Adhikari
authors: Center for Geomicrobiology, Department of Bioscience, Aarhus University Aarhus C, Denmark.
authors: Clemens
authors: C
authors: Glombitza
authors: Geomicrobiology Group, Institute of Earth and Environmental Science, University of PotsdamPotsdam, Germany; Helmholtz-Centre Potsdam - GFZ German Research Centre for GeosciencesPotsdam, Germany.
authors: Julia C
authors: JC
authors: Nickel
authors: Department of Earth and Environment, Boston University Boston, MA, USA.
authors: Chloe H
authors: CH
authors: Anderson
authors: Department of Earth and Environment, Boston University Boston, MA, USA.
authors: Ann G
authors: AG
authors: Dunlea
authors: Graduate School of Oceanography, University of Rhode Island Kingston, RI, USA.
authors: Arthur J
authors: AJ
authors: Spivack
authors: Department of Earth and Environment, Boston University Boston, MA, USA.
authors: Richard W
authors: RW
authors: Murray
authors: Graduate School of Oceanography, University of Rhode Island Kingston, RI, USA.
authors: Steven
authors: S
authors: D'Hondt
authors: Geomicrobiology Group, Institute of Earth and Environmental Science, University of PotsdamPotsdam, Germany; Helmholtz-Centre Potsdam - GFZ German Research Centre for GeosciencesPotsdam, Germany.
authors: Jens
authors: J
authors: Kallmeyer
keywords: Barents Sea; Equatorial Pacific; Gulf of Mexico; Lake Van; deep biosphere; hydrogenase; microbial activity; tritium assay