Formate-driven H 2 production by whole cells of Thermoanaerobacter kivui

Background In times of global warming there is an urgent need to replace fossil fuel-based energy vectors by less carbon dioxide (CO 2 )-emitting alternatives. One attractive option is the use of molecular hydrogen (H 2 ) since its combustion emits water (H 2 O) and not CO 2 . Therefore, H 2 is regarded as a non-polluting fuel. The ways to produce H 2 can be diverse, but steam reformation of conventional fossil fuel sources is still the main producer of H 2 gas up to date. Biohydrogen production via microbes could be an alternative, environmentally friendly and renewable way of future H 2 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 2 production by whole cells of the thermophilic acetogenic bacterium Thermoanaerobacter kivui which harbors a highly active hydrogen-dependent CO 2 reductase (HDCR) to oxidize formate to H 2 and CO 2 and vice versa. Under optimized reaction conditions, T. kivui cells demonstrated the highest H 2 production rates (qH 2 = 685 mmol g −1 h −1 ) which were so far reported in the literature for wild-type organisms. Additionally, high yields ( Y (H2/formate) ) of 0.86 mol mol −1 and a hydrogen evolution rate (HER) of 999 mmol L −1 h −1 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 2 production. Conclusions The thermophilic acetogenic bacterium T. kivui is an efficient biocatalyst for the oxidation of formate to H 2 (and CO 2 ). 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 2 bio-economy.