Stimulation of hydrogen photoproduction in Chlorella Sorokiniana subjected to simultaneous nitrogen limitation and sulfur-and/or phosphorus-deprivation

Photosynthetic hydrogen (H ₂ ) production by green algae has fascinated biologists and energy experts, due to the potential application of this process for renewable energy. In this study, H ₂ photoproduction and PSII photochemical activities were investigated in Chlorella sorokiniana exposed to simultaneous nitrogen limitation and sulfur (S-) and/or phosphorus (P-) deprivation. Under S-deprivation, C. sorokiniana produced about 48.2 mL L ^-1 of H ₂ . Moreover, simultaneous nitrogen limitation (0.7 mM NH ₄ Cl) and sulfur-and/or phosphorus-deprivation significantly increased H ₂ production of C. sorokiniana over that of S-deprivation alone. Maximum H ₂ outputs of 77.3, 98.1 and 125.1 mL L ^-1 were obtained in the N-limited cultures exposed to P-deprivation (TAP-P), S-deprivation (TAP-S) and simultaneous S-and P-deprivation (TAP-S-P), respectively. The average rate of H ₂ production for the N-limited culture exposed to TAP-P, TAP-S and TAP-S-P was 1.07, 1.36 and 1.50 mL L ^-1 h ^-1 , respectively. Interestingly, the H ₂ inducement time in the culture subjected to simultaneous N-limitation and S-and/or P-deprivation was much shorter than that of traditional S-deprivation. The photosynthetic inhibitors, 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea (DCMU) and 2, 5-dibromo-3-methyl-6-isopropylp-benzoquinone (DBMIB) repressed H ₂ production in TAP-S-P (0.7 mM NH ₄ Cl) medium by 68.04% and 98.65%, respectively. The conditions of simultaneous N-limitation, S-and P-deprivation provided another efficient method for inducing H ₂ production in C. sorokiniana. In addition, we also found that two-thirds of the required electrons were generated from the splitting of H ₂ O in PSII and that the remaining one-third possibly came from some other substrate catabolism.