Bio-hydrogen production under pressure by pressure-adapted subsurface microbes

Microorganisms can produce bio-hydrogen (H2) during their metabolism, and especially dark fermentative production from carbohydrates is a promising option. However, the technology still suffers from low H2 production rates due to product inhibition of the H2-producing enzymes. In this study we investigate if subsurface (reservoir) microbes can be relevant bio-H2 producers and a source of high-pressure adapted enzymes. In addition, we also investigate the potential H2 productivity using an indigenous reservoir community, thereby proposing a preliminary screening workflow for mature oil fields to be used as potential in-situ H2 bioreactors. We cultured two H2-producers Marinitoga hydrogenitolerans and Thermotoga napthophila, which were isolated from high-pressure environments, and a freshly obtained oil reservoir brine containing a fermentative community under atmospheric and pressurized conditions (15–16 bar). All cultures produced H2 under atmospheric conditions with different productivities. Marinitoga shows the same cell number increase and glucose consumption under high pressure compared to atmospheric but with a significantly decreased H2 productivity of −86%. The productivity decline of the reservoir community was less pronounced with −35%. The mole fraction of H2 in the produced gas was in both cases high (0.64 and 0.82 respectively). Our results indicate strong differences in the pressure-related enzyme adaptations and may be used for screening of pressure-tolerant microbes and enzymes for enhanced bio-H2 production.