title: Serpentinization-Influenced Groundwater Harbors Extremely Low Diversity Microbial Communities Adapted to High pH.
abstract: Serpentinization is a widespread geochemical process associated with aqueous alteration of ultramafic rocks that produces abundant reductants (H2and CH4) for life to exploit, but also potentially challenging conditions, including high pH, limited availability of terminal electron acceptors, and low concentrations of inorganic carbon. As a consequence, past studies of serpentinites have reported low cellular abundances and limited microbial diversity. Establishment of the Coast Range Ophiolite Microbial Observatory (California, U.S.A.) allowed a comparison of microbial communities and physicochemical parameters directly within serpentinization-influenced subsurface aquifers. Samples collected from seven wells were subjected to a range of analyses, including solute and gas chemistry, microbial diversity by 16S rRNA gene sequencing, and metabolic potential by shotgun metagenomics, in an attempt to elucidate what factors drive microbial activities in serpentinite habitats. This study describes the first comprehensive interdisciplinary analysis of microbial communities in hyperalkaline groundwater directly accessed by boreholes into serpentinite rocks. Several environmental factors, including pH, methane, and carbon monoxide, were strongly associated with the predominant subsurface microbial communities. A single operational taxonomic unit (OTU) of Betaproteobacteria and a few OTUs of Clostridia were the almost exclusive inhabitants of fluids exhibiting the most serpentinized character. Metagenomes from these extreme samples contained abundant sequences encoding proteins associated with hydrogen metabolism, carbon monoxide oxidation, carbon fixation, and acetogenesis. Metabolic pathways encoded by Clostridia and Betaproteobacteria, in particular, are likely to play important roles in the ecosystems of serpentinizing groundwater. These data provide a basis for further biogeochemical studies of key processes in serpentinite subsurface environments.
authors.affiliation: Department of Microbiology and Molecular Genetics, Michigan State University, East LansingMI, USA; Department of Biology, University of Utah, Salt Lake CityUT, USA.
authors.forename: Katrina I
authors.initials: KI
authors.lastname: Twing
authors.affiliation: Department of Biology, University of Utah, Salt Lake City UT, USA.
authors.forename: William J
authors.initials: WJ
authors.lastname: Brazelton
authors.affiliation: SETI Institute, Mountain View CA, USA.
authors.forename: Michael D Y
authors.initials: MD
authors.lastname: Kubo
authors.affiliation: Department of Biology, University of Utah, Salt Lake City UT, USA.
authors.forename: Alex J
authors.initials: AJ
authors.lastname: Hyer
authors.affiliation: Department of Geosciences, University of Rhode Island, Kingston RI, USA.
authors.forename: Dawn
authors.initials: D
authors.lastname: Cardace
authors.affiliation: Exobiology Branch, NASA Ames Research Center, Moffett Field CA, USA.
authors.forename: Tori M
authors.initials: TM
authors.lastname: Hoehler
authors.affiliation: Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder CO, USA.
authors.forename: Tom M
authors.initials: TM
authors.lastname: McCollom
authors.affiliation: Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing MI, USA.
authors.forename: Matthew O
authors.initials: MO
authors.lastname: Schrenk
keywords: alkaliphile; borehole; extremophile; groundwater; serpentinization