Optimization of the yield of dark microaerobic production of hydrogen from lactate by Rhodopseudomonas palustris

Hydrogen yields of dark fermentation are limited due to the need to also produce reduced side products, and photofermentation, an alternative, is limited by the need for light. A relatively new strategy, dark microaerobic fermentation, could potentially overcome both these constraints. Here, application of this strategy demonstrated for the first time significant hydrogen production from lactate by a single organism in the dark. Response surface methodology (RSM) was used to optimize substrate and oxygen concentration as well as inoculum using both (1) regular batch and (2) O2 fed batch cultures. The highest hydrogen yield (HY) was observed under regular batch (1.4 ± 0.1 mol H2/mol lactate) and the highest hydrogen production (HP) (173.5 µmol H2) was achieved using O2 fed batch. This study has provided proof of principal for the ability of microaerobic fermentation to drive thermodynamically difficult reactions, such as the conversion of lactate to hydrogen.