Stimulation of Hydrogen Photoproduction in Chlorella sorokiniana Subjected to Simultaneous Nitrogen Limitation and Sulfur- and/or Phosphorus-Deprivation

Photosynthetic hydrogen (H2) production by green algae has fascinated biologists and energy experts, due to the potential application of this process for renewable energy. In this study, H2 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 H2. Moreover, simultaneous nitrogen limitation (0.7 mM NH4Cl) and sulfurand/or phosphorus-deprivation significantly increased H2 production of C. sorokiniana over that of S-deprivation alone. Maximum H2 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 Sand P-deprivation (TAP-S-P), respectively. The average rate of H2 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 H2 inducement time in the culture subjected to simultaneous N-limitation and Sand/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 H2 production in TAP-S-P (0.7 mM NH4Cl) medium by 68.04% and 98.65%, respectively. The conditions of simultaneous N-limitation, Sand P-deprivation provided another efficient method for inducing H2 production in C. sorokiniana. In addition, we also found that two-thirds of the required electrons were generated from the splitting of H2O in PSII and that the remaining onethird possibly came from some other substrate catabolism.