Improvement of hydrogen yield by hupR gene knock-out and nifA gene overexpression in Rhodobacter sphaeroides 6016

Purple non-sulfur (PNS) bacteria produce hydrogen under photoheterotrophic conditions. The produced hydrogen, which is catalyzed by Mo-nitrogenase, is re-oxidized by a membrane-bound uptake hydrogenase. To improve hydrogen-producing efficiency, the hupSL gene that encodes the uptake hydrogenase, and its positive regulator gene hupR were knocked out in Rhodobacter sphaeroides 6016. Compared to the wild-type strain, the hydrogen yields of the hupSL− and hupR− mutants each increased by 11%. When the nifA gene, which encodes a specific transcriptional activator for all other nif genes was overexpressed in the hupR− mutant, the hydrogen yield increased by 20%. In addition, hydrogen production was detected in the nifA/hupR− mutant in the presence of 14 mM NH4+, whereas the wild-type strain produced no hydrogen under the same conditions.