The enhancement of hydrogen photoproduction in marine Chlorella pyrenoidosa under nitrogen deprivation

Previously, we found that marine Chlorella pyrenoidosa strain IOAC707S could generate hydrogen (H2) under nitrogen deprivation in seawater medium, without dark incubation, N2 flushing or addition of protonophore. In this work, the H2 yield of C. pyrenoidosa was enhanced, and the mechanism of H2 photoproduction was investigated. It was found that C. pyrenoidosa could produce H2 under hypoxic conditions, which indicated the hydrogenase of C.pyrenoidosa could tolerate a low concentration of O2. Nitrogen deprivation could lower the efficiency of photosyntem (PS) II photochemical activity and PSII oxygenic activities, which were favorable for rapid establishment of anoxia and efficient H2 photoproduction, and thus significantly enhance H2 photoproduction of C. pyrenoidosa. Pre-culture in nitrogen-deprived medium could further increase the H2 yield of C. pyrenoidosa, for its more severe inhibition of the oxygen-evolving complex, electron transport and photochemical efficiency of PSII, and PSII oxygenic activities, which facilitated the establishment of anaerobiosis and activation of hydrogenase.