Sulfide as electron source for H 2-photoproduction in the cyanobacterium Synechococcus sp., strain Miami BG 043511, under stress conditions

Abstract

Synechococcus sp., strain Miami BG 043511, was used as biological material to examine whether cyanobacteria, like photosynthetic bacteria, can utilize sulfide as electron source for H 2 photoproduction. We found that sulfide can have either an inhibiting or a stimulating effect on the H 2 production of the cyanobacterium, depending on growth conditions, age and sulfide concentration in the nutrient solution. When sodium sulfide (more than 5 mM) was added, H 2 production was inhibited in three-day-old cells. The inhibition was negligible with seven-day-old cells, whereas a stimulating effect was measured with 15-day-old cells in the stationary growth phase. At the latter stage the limited light intensity and the deficiency in nutrients represent extreme stress conditions for the organism. The stimulating effect of sulfide under these stress conditions could be enhanced by increasing sulfide concentrations. The stimulating effect of sulfide on H 2 production was further confirmed by administering gradually increasing sulfide concentrations to immobilized cells. Our results suggest that Synechococcus sp. strain Miami BG 043511 is able to use sulfide as electron donor for H 2 photoproduction, especially under stress conditions.