Factors affecting biohydrogen production by unicellular halotolerant cyanobacterium Aphanothece halophytica

The effects of several physiological parameters on H-2 production rate in the unicellular halotolerant cyanobacterium Aphanothece halophytica were investigated. Under nitrogen deprivation, the growth of cells was inhibited, but H-2 production rate was enhanced approximately fourfold. Interestingly, cells grown under sulfur deprivation exhibited a decrease in cell growth, H-2 production rate, and bidirectional hydrogenase activity. Glucose was the preferred sugar source for H-2 production by A. halophytica, but H-2 production decreased at high glucose concentrations. H-2 production rate was optimum when cells were grown in the presence of 0.75 M NaCl, or 0.4 mu M Fe3+, or 1 mu M Ni2+. The optimum light intensity and temperature for H-2 production were 30 mu mol photons m(-2) s(-1) and 35 A degrees C, respectively. A two-stage culture of A. halophytica was performed in order to overcome the reduction of cell growth in N-free medium. In the first stage, cells were grown in normal medium to accumulate biomass, and in the second stage, H-2 production by the obtained biomass was induced by growing cells in N-free medium supplemented with various chemicals for 24 h. A. halophytica grown in N-free medium containing various MgSO4 concentrations had a high H-2 production rate between 11.432 and 12.767 mu mol H-2 mg chlorophyll a (chl a)(-1) h(-1), a 30-fold increase compared to cells grown in normal medium. The highest rate of 13.804 mu mol H-2 mg chl a (-1) h(-1) was obtained when the N-free growth medium contained 0.4 mu M Fe3+. These results suggested the possibility of using A. halophytica and some other halotolerant cyanobacteria thriving under extreme environmental conditions in the sea as potential sources for H-2 production in the future.