Pressure up to 60 bar has no major effect on the overall hydrogen consumption of the sulfate reducer Oleidesulfovibrio alaskensis

Abstract Aims Subsurface environments found in geological aquifers or reservoirs are not sterile but harbor diverse microbial communities for which hydrogen (H2) is a ubiquitous electron donor, especially for sulfate-reducing bacteria (SRB). Most studies investigating SRBs have been performed consumption experiments at near-atmospheric pressure. However, pressures are significantly higher in subsurface formations. It remains a crucial question whether high H2 partial pressure influences microbial consumption. Therefore, we tested a relevant SRB under increased H2-pressure to investigate changes in H2-consumption behavior. Methods and results We cultured the H2-consuming SRB Oleidesulfovibrio alaskensis G20 under 1, 30, and 60 bar of H2 overpressure and quantified consumption over time. Data were compared to sterile incubations. After 16 days, the total amount of consumed H2, sulfate and acetate was similar for all pressure conditions and pH ended over 9, which is beyond the described pH limit. While the maximum H2 consumption rate was found higher at atmospheric pressures (0.20 mmol per day) compared to 30 and 60 bar (0.13 and 0.11 mmol per day), the maximum rate per surface area was comparable (0.02, 0.03, 0.02 mmol per day per cm2). The total rate of H2 consumption per cm2 was higher with increasing pressure, which is probably related to the increased solubility of H2 in the brine phase due to pressure. Conclusions The data shows that pressures up to 60 bar have no significant effect on the overall activity of O. alaskensis. The governing factor for the H2 consumption rate is contact area between brine and gas phase and the concentration of dissolved H2.