Monitoring of the microbial community composition in deep subsurface saline aquifers during CO2 storage in Ketzin, Germany

This study characterized the composition and activity of the autochthonous microbial community in formation fluids of a saline CO2 storage aquifer during CO2 injection and during an N2 lift. The clean-up of the wells prior CO2 injection by N2 lift decreased the total microbial cell numbers, and the number of sulphate reducing bacteria (SRB) was reduced by at least two orders of magnitude. Fluorescence in situ Hybridisation (FISH) and molecular fingerprinting demonstrated that the microbial community was strongly influenced by the CO2 injection. Before CO2 arrival, up to 106 cells ml-1 were detected by DAPI-staining at a depth of 647 m below the surface. The microbial community was dominated by fermentative halophilic bacteria and sulphate reducing bacteria. Both the FISH and fingerprinting analyses revealed quantitative and qualitative changes after CO2 arrival. An enhanced activity and quantity of the microbial population after five months of CO2 storage indicated that the community was able to adapt to the extreme conditions of the deep biosphere and to the extreme changes of these anthropogenically modified conditions.