The effect of cycA overexpression on hydrogen production performance of Rhodobacter sphaeroides HY01

The gene cycA encodes a periplasmic protein, cytochrome c2 (cyt c2), which dominates electron transfer from the membrane-bound ubiquinol: cyt c2 oxidoreductase (cyt bc1) to the photosynthetic reaction center, contributing to the production of transmembrane proton potential and then the synthesis of ATP. For photosynthetic bacteria, the total energy supply for light anaerobic growth and hydrogen production comes from photophosphorylation. As a result, the key protein encoding gene plays an important role in hydrogen production. To figure out the specific effect of cycA expression level on H2 production ability of Rhodobacter sphaeroides HY01, cycA-expression plasmids derived from pRK415 and pBBR1MCS-2 were constructed and then crossed into the parent strain R. sphaeroides HY01 for H2 production test. And further verification by RT-PCR suggested that there was about 20% enhancement of cycA expression level by pBBR1MCS-2 where the H2 production performance of corresponding strain was improved by 6–8% compared with blank control. In contrast, cycA expression level was about 3.4 folds by vector pRK415 compared with control strain, but corresponding strains showed slightly depressed H2 production performance. Besides, the mutant XJ01 with cycA gene overexpressing by 70% in the genome of HY01(hupSL:cycA) also showed positive effect on hydrogen production performance. The results demonstrated that slightly overexpression of cycA could enhance the hydrogen production rate, but too much higher level of cycA-expression could show negative effect on H2 production performance of R. sphaeroides HY01.