SULFIDE AS ELECTRON SOURCE FOR H-2-PHOTOPRODUCTION IN THE CYANOBACTERIUM SYNECHOCOCCUS SP, STRAIN MIAMI BG-043511, UNDER STRESS CONDITIONS

Synechococcus sp., strain Miami BG 043511, was used as biological mate rial to examine whether cyanobacteria, like photosynthetic bacteria, c an utilize sulfide as electron source for H-2 photoproduction. We foun d that sulfide can have either an inhibiting or a stimulating effect o n the H-2 production of the cyanobacterium, depending on growth condit ions, age and sulfide concentration in the nutrient solution. When sod ium sulfide (more than 5 mM) was added, H-2 production was inhibited i n three-day-old cells. The inhibition was negligible with seven-day-ol d cells, whereas a stimulating effect was measured with 15-day-old cel ls in the stationary growth phase. At the latter stage the limited lig ht intensity and the deficiency in nutrients represent extreme stress conditions for the organism. The stimulating effect of sulfide under t hese stress conditions could be enhanced by increasing sulfide concent rations. The stimulating effect of sulfide on H-2 production was furth er confirmed by administering gradually increasing sulfide concentrati ons to immobilized cells. Our results suggest that Synechococcus sp. s train Miami BG 043511 is able to use sulfide as electron donor for H-2 photoproduction, especially under stress conditions.