Response of H2 production and Hox-hydrogenase activity to external factors in the unicellular cyanobacterium Synechocystis sp. strain PCC 6803

The effects of external factors on both H2 production and bidirectional Hox-hydrogenase activity were examined in the non-N2-fixing cyanobacterium Synechocystis PCC 6803. Exogenous glucose and increased osmolality both enhanced H2 production with optimal production observed at 0.4% and 20 mosmol kg−1, respectively. Anaerobic condition for 24 h induced significant higher H2ase activity with cells in BG110 showing highest activities. Increasing the pH resulted in an increased Hox-hydrogenase activity with an optimum at pH 7.5. The Hox-hydrogenase activity gradually increased with increasing temperature from 30 ○C to 60 ○C with the highest activity observed at 70 ○C. A low concentration at 100 μM of either DTT or β-mercaptoethanol resulted in a minor stimulation of H2 production. β-Mercaptoethanol added to nitrogen- and sulfur-deprived cells stimulated H2 production significantly. The highest Hox-hydrogenase activity was observed in cells in BG110-S-deprived condition and 750 μM β-mercaptoethanol measured at a temperature of 70 °C; 14.32 μmol H2 mg chl a−1 min−1.