Assessment of Eger Rift subsurface microbial communities showcases archaeal and bacterial processes driven by mantel derived CO2 degassing and regular seismic events.

Seismic activity and consistently high CO₂ fluxes make the Eger Rift in Western Bohemia (CZ) a rare subsurface ecosystem and scientifically relevant location to study microbial behavior and assess how geologically derived compound are used in the deep subsurface. Studying microbial life in this ecosystem provides the opportunity to investigate how high CO₂ levels and mineralogy influence microbial community composition and metabolic activity. Seismic activity in this region can also release H₂, a process which may provide the basis for primary production through methanogenic archaea and should be explored.

To assess microbial processes associated with the Eger Rift subsurface we investigated diversity, community structure and metabolic attributes of bacterial and archaeal communities in drill core sediments and groundwater samples. We also analyzed the geochemical conditions in this subsurface system and studied the physiological responses of native Eger microbial communities to high CO₂ via enrichments

Genomic analysis of sediment and water samples, covering depths between 17m and 230m, provided novel insights into a CO₂ adapted microbial community. We detected strong Cyanobacteria and Proteobacteria signatures as well as unexpected archaeal diversity in sediments, and high abundances of acidophiles and sulfate reducers in water samples. Enrichment cultures from the recovered sediments suggested subsurface populations can actively utilize CO₂ and H₂, while reconstruction and annotation of MAGs provided insights into microbial processes driven by CO₂.

Going forward our data will be used to further investigate cellular processes under high CO₂ conditions and identify pathways and biomolecules which may be of industrial and biotechnological relevance.