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.