A Stepwise NaHSO(3) Addition Mode Greatly Improves H(2) Photoproduction in Chlamydomonas reinhardtii

NaHSO(3) addition greatly increases the yield of H(2) photoproduction in a unicellular green alga Chlamydomonas reinhardtii through removing O(2) and activating hydrogenase but significantly impairs the activity of PSII, an electron source for H(2) photoproduction. Here, a stepwise addition mode of total 13 mM NaHSO(3), an optimal concentration for H(2) photoproduction of C. reinhardtii identified in a previous one step addition method, significantly improved H(2) photoproduction. Such improvement was believed to be the result of increased residual PSII activity in an anaerobic background, but was at least independent of two alternative electron sinks for H(2) photoproduction, cyclic electron transport around PSI and CO(2) assimilation. Based on the above results, we propose that increased residual PSII activity in an anaerobic environment is an efficient strategy to enhance H(2) photoproduction in C. reinhardtii, and the stepwise NaHSO(3) addition mode is a case study in the strategy.