, Volume 25, Issue 2, pp 575-585
Date: 31 Aug 2012

Factors affecting biohydrogen production by unicellular halotolerant cyanobacterium Aphanothece halophytica

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Abstract

The effects of several physiological parameters on H2 production rate in the unicellular halotolerant cyanobacterium Aphanothece halophytica were investigated. Under nitrogen deprivation, the growth of cells was inhibited, but H2 production rate was enhanced approximately fourfold. Interestingly, cells grown under sulfur deprivation exhibited a decrease in cell growth, H2 production rate, and bidirectional hydrogenase activity. Glucose was the preferred sugar source for H2 production by A. halophytica, but H2 production decreased at high glucose concentrations. H2 production rate was optimum when cells were grown in the presence of 0.75 M NaCl, or 0.4 μM Fe3+, or 1 μM Ni2+. The optimum light intensity and temperature for H2 production were 30 μmol photons m−2 s−1 and 35 °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, H2 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 H2 production rate between 11.432 and 12.767 μmol H2 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 μmol H2 mg chl a −1 h−1 was obtained when the N-free growth medium contained 0.4 μM 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 H2 production in the future.