BACKGROUND

In times of global warming there is an urgent need to replace fossil fuel-based energy vectors by less carbon dioxide (CO)-emitting alternatives. One attractive option is the use of molecular hydrogen (H) since its combustion emits water (HO) and not CO. Therefore, H is regarded as a non-polluting fuel. The ways to produce H can be diverse, but steam reformation of conventional fossil fuel sources is still the main producer of H gas up to date. Biohydrogen production via microbes could be an alternative, environmentally friendly and renewable way of future H production, especially when the flexible and inexpensive C1 compound formate is used as substrate.

RESULTS

In this study, the versatile compound formate was used as substrate to drive H production by whole cells of the thermophilic acetogenic bacterium Thermoanaerobacter kivui which harbors a highly active hydrogen-dependent CO reductase (HDCR) to oxidize formate to H and CO and vice versa. Under optimized reaction conditions, T. kivui cells demonstrated the highest H production rates (qH = 685 mmol g h) which were so far reported in the literature for wild-type organisms. Additionally, high yields (Y) of 0.86 mol mol and a hydrogen evolution rate (HER) of 999 mmol L h were observed. Finally, stirred-tank bioreactor experiments demonstrated the upscaling feasibility of the applied whole cell system and indicated the importance of pH control for the reaction of formate-driven H production.

CONCLUSIONS

The thermophilic acetogenic bacterium T. kivui is an efficient biocatalyst for the oxidation of formate to H (and CO). The existing genetic tool box of acetogenic bacteria bears further potential to optimize biohydrogen production in future and to contribute to a future sustainable formate/H bio-economy.