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 (H2) during oxygenic photosynthesis. Addition of protonophores, carbonyl cyanide m-chlorophenylhydrazone (CCCP) and 2,4-dinitrophenol (DNF) enhances H2 yield in P. kessleri. The maximal H2 yield of ~2.20 and 2.08 mmol L-1 was obtained in the presence of 15 μM CCCP and 50 μM DNF, respectively. During dark conditions H2 production by P. kessleri was not observed even in the presence of protonophores, indicating that H2 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 H2. At the same time H2 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 H2 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 H2 generation. This study is important for understanding of the mechanisms of H2 production by green microalgae P. kessleri and developing of its biotechnology.