Regulation of biohydrogen production by protonophores in novel green microalgae Parachlorella kessleri

The green microalgae Parachlorella kessleri RA-002 isolated in Armenia can produce biohydrogen (H-2) during oxygenic photosynthesis. Addition of protonophores, carbonyl cyanide m-chlorophenylhydrazone (CCCP) and 2,4-dinitrophenol (DNF) enhances H-2 yield in P. kessleri. The maximal H-2 yield of similar to 2.20 and 2.08 mmol L-1 was obtained in the presence of 15 mu M CCCP and 50 mu M DNF, respectively. During dark conditions H-2 production by P. kessleri was not observed even in the presence of protonophores, indicating that H-2 formation in these algae was mediated by light conditions. The enhancing effect of protonophores can be coupled with dissipation of proton motive force across thylakoid membrane in P. kessleri, facilitating the availability of protons and electrons to [Fe-Fe]-hydrogenase, which led to formation of H-2. At the same time H-2 production was not observed in the presence of diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea), a specific inhibitor of PS II. Moreover, diuron inhibits H-2 yield in P. kessleri in the presence of protonophores. The inhibitory effect of diuron coupled with suppression of electron transfer from PS II. The results showed that in these algae operates PS II-dependent pathway of H-2 generation. This study is important for understanding of the mechanisms of H-2 production by green microalgae P. kessleri and developing of its biotechnology.