CO(2) exposure at pressure impacts metabolism and stress responses in the model sulfate-reducing bacterium Desulfovibrio vulgaris strain Hildenborough

Geologic carbon dioxide (CO(2)) sequestration drives physical and geochemical changes in deep subsurface environments that impact indigenous microbial activities. The combined effects of pressurized CO(2) on a model sulfate-reducing microorganism, Desulfovibrio vulgaris, have been assessed using a suite of genomic and kinetic measurements. Novel high-pressure NMR time-series measurements using (13)C-lactate were used to track D. vulgaris metabolism. We identified cessation of respiration at CO(2) pressures of 10 bar, 25 bar, 50 bar, and 80 bar. Concurrent experiments using N(2) as the pressurizing phase had no negative effect on microbial respiration, as inferred from reduction of sulfate to sulfide. Complementary pressurized batch incubations and fluorescence microscopy measurements supported NMR observations, and indicated that non-respiring cells were mostly viable at 50 bar CO(2) for at least 4 h, and at 80 bar CO(2) for 2 h. The fraction of dead cells increased rapidly after 4 h at 80 bar CO(2). Transcriptomic (RNA-Seq) measurements on mRNA transcripts from CO(2)-incubated biomass indicated that cells up-regulated the production of certain amino acids (leucine, isoleucine) following CO(2) exposure at elevated pressures, likely as part of a general stress response. Evidence for other poorly understood stress responses were also identified within RNA-Seq data, suggesting that while pressurized CO(2) severely limits the growth and respiration of D. vulgaris cells, biomass retains intact cell membranes at pressures up to 80 bar CO(2). Together, these data show that geologic sequestration of CO(2) may have significant impacts on rates of sulfate reduction in many deep subsurface environments where this metabolism is a key respiratory process.