Enhanced photosynthetic hydrogen production performance of Rhodobacter capsulatus by deactivating CBB cycle and cytochrome c oxidase

• Wb301 (ΔccoNOQP), Wbp02 (ΔcbbP) and W3p03 (ΔcbbP, ΔccoNOQP) were constructed.
• The nifH expression levels were enhanced clearly when ccoNOQP was deleted.
• Hydrogen production was conducted in two reactors with different optical path.
• The hydrogen yields and hydrogen production rates of the mutants were enhanced.

The effect of redox balance on photosynthetic bacteria growth and hydrogen generation is significant since it affects the distribution of electron flow. In this study, cbbP encoding the key enzymes in CO2 fixation cycle, and ccoNOQP encoding cyt cbb3 oxidase in cytochrome respiratory chain, were knocked out from the genome of Rhodobacter capsulatus SB1003 to obtain the mutants Wb301 (ΔccoNOQP), Wbp02 (ΔcbbP) and W3p03 (ΔcbbP, ΔccoNOQP). The transcriptional and translational level of nifH gene showed that the nifH expression levels in Wb301 and W3p03 were enhanced by 93.5% and 62.5%, and the activities of nitrogenase of Wb301 and W3p03 were enhanced by 30% and 10%, compared with those of wild type strain, respectively. In 60 mL reactors, the hydrogen yields of Wb301 and W3p03 increased by 44.8% and 36.0%, and the maximum hydrogen evolution rates increased by 15.8% and 41.7% compared with that of the wild type, respectively. The mechanisms of CBB and cytochrome c oxidase deactivation on the growth and hydrogen production performance were discussed.