Microbial potential for carbon and nutrient cycling in a geogenic supercritical carbon dioxide reservoir

Abstract

Microorganisms catalyze carbon cycling and biogeochemical reactions in the deep subsurface and thus may be expected to influence the fate of injected supercritical (sc) CO₂ following geological carbon sequestration (GCS). We hypothesized that natural subsurface scCO₂ reservoirs, which serve as analogs for the long-term fate of sequestered scCO₂, harbor a ‘deep carbonated biosphere’ with carbon cycling potential. We sampled subsurface fluids from scCO₂-water separators at a natural scCO₂ reservoir at McElmo Dome, Colorado for analysis of 16S rRNA gene diversity and metagenome content. Sequence annotations indicated dominance of Sulfurospirillum, Rhizobium, Desulfovibrio and four members of the Clostridiales family. Genomes extracted from metagenomes using homology and compositional approaches revealed diverse mechanisms for growth and nutrient cycling, including pathways for CO₂ and N₂ fixation, anaerobic respiration, sulfur oxidation, fermentation and potential for metabolic syntrophy. Differences in biogeochemical potential between two production well communities were consistent with differences in fluid chemical profiles, suggesting a potential link between microbial activity and geochemistry. The existence of a microbial ecosystem associated with the McElmo Dome scCO₂ reservoir indicates that potential impacts of the deep biosphere on CO2fate and transport should be taken into consideration as a component of GCS planning and modelling.