Carbon Assimilation Strategies in Ultrabasic Groundwater: Clues from the Integrated Study of a Serpentinization-Influenced Aquifer

Lauren M Seyler; William J Brazelton; Craig McLean; Lindsay I Putman; Alex Hyer; Michael D Y Kubo; Tori Hoehler; Dawn Cardace; Matthew O Schrenk

doi:10.1128/mSystems.00607-19

Carbon Assimilation Strategies in Ultrabasic Groundwater: Clues from the Integrated Study of a Serpentinization-Influenced Aquifer

mSystems. 2020 Mar 10;5(2):e00607-19. doi: 10.1128/mSystems.00607-19.

Authors

Lauren M Seyler^{1

2}, William J Brazelton³, Craig McLean^{4

5}, Lindsay I Putman⁶, Alex Hyer³, Michael D Y Kubo^{2

7}, Tori Hoehler⁷, Dawn Cardace⁸, Matthew O Schrenk^{6

9}

Affiliations

¹ Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA lmseyler@gmail.com.
² Blue Marble Space Institute of Science, Seattle, Washington, USA.
³ Department of Biology, University of Utah, Salt Lake City, Utah, USA.
⁴ Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA.
⁵ Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
⁶ Department of Earth and Environmental Sciences, Michigan State University, East Lansing, Michigan, USA.
⁷ Space Sciences Division, NASA Ames Research Center, Mountain View, California, USA.
⁸ Department of Geosciences, University of Rhode Island, Kingston, Rhode Island, USA.
⁹ Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA.

Abstract

Serpentinization is a low-temperature metamorphic process by which ultramafic rock chemically reacts with water. Such reactions provide energy and materials that may be harnessed by chemosynthetic microbial communities at hydrothermal springs and in the subsurface. However, the biogeochemistry mediated by microbial populations that inhabit these environments is understudied and complicated by overlapping biotic and abiotic processes. We applied metagenomics, metatranscriptomics, and untargeted metabolomics techniques to environmental samples taken from the Coast Range Ophiolite Microbial Observatory (CROMO), a subsurface observatory consisting of 12 wells drilled into the ultramafic and serpentinite mélange of the Coast Range Ophiolite in California. Using a combination of DNA and RNA sequence data and mass spectrometry data, we found evidence for several carbon fixation and assimilation strategies, including the Calvin-Benson-Bassham cycle, the reverse tricarboxylic acid cycle, the reductive acetyl coenzyme A (acetyl-CoA) pathway, and methylotrophy, in the microbial communities inhabiting the serpentinite-hosted aquifer. Our data also suggest that the microbial inhabitants of CROMO use products of the serpentinization process, including methane and formate, as carbon sources in a hyperalkaline environment where dissolved inorganic carbon is unavailable.IMPORTANCE This study describes the potential metabolic pathways by which microbial communities in a serpentinite-influenced aquifer may produce biomass from the products of serpentinization. Serpentinization is a widespread geochemical process, taking place over large regions of the seafloor and at continental margins, where ancient seafloor has accreted onto the continents. Because of the difficulty in delineating abiotic and biotic processes in these environments, major questions remain related to microbial contributions to the carbon cycle and physiological adaptation to serpentinite habitats. This research explores multiple mechanisms of carbon fixation and assimilation in serpentinite-hosted microbial communities.

Keywords: carbon assimilation; carbon fixation; formaldehyde; formate; methane; serpentinization.