Metagenomic analysis of a high CO2 subsurface microbial community populated by chemolithoautotrophs and bacteria and archaea from candidate phyla
Joanne B. Emerson,
Brian C. Thomas,
Walter Alvarez and
Jillian F. Banfield
Department of Earth and Planetary Science, 307 McCone Hall, University of California, Berkeley, Berkeley, CA, 94720-4767, USA.
Research on geologic carbon sequestration raises questions about potential impacts of subsurface microbiota on carbon cycling and biogeochemistry. Subsurface, high-CO2 systems are poorly biologically characterized, partly due to difficulty accessing high-volume, uncontaminated samples. CO2–driven Crystal Geyser (Utah, USA), an established geologic carbon sequestration analog, provides high volumes of deep (∼200-500 m) subsurface fluids. We explored microbial diversity and metabolic potential in this high-CO2 environment by assembly and analysis of metagenomes recovered from geyser water filtrate. The system is dominated by neutrophilic, iron-oxidizing bacteria, including “marine” Mariprofundus (Zetaproteobacteria) and “freshwater” Gallionellales, sulfur-oxidizing Thiomicrospira crunogena, and Thiobacillus-like Hydrogenophilales. Near-complete genomes were reconstructed for these bacteria. Crystal Geyser is notably populated by a wide diversity of bacteria and archaea from phyla lacking isolated representatives (Candidate Phyla, CP) and from as-yet undefined lineages. Many bacteria affiliate with OD1, OP3, OP9, PER, ACD58, WWE3, BD1-5, OP11, TM7, and ZB2. The recovery of nearly 100 genes encoding RuBisCO subunit proteins of the Calvin Cycle and AMP salvage pathways suggests a strong biological role in high-CO2 subsurface carbon cycling. Overall, we predict microbial impacts on subsurface biogeochemistry via iron, sulfur, and complex carbon oxidation, carbon and nitrogen fixation, fermentation, hydrogen metabolism, and aerobic and anaerobic respiration.