Influence of sulfate-reducing bacteria, sulfide and molybdate on hydrogen photoproduction by purple nonsulfur bacteria

The interaction between bacterial species is of great importance for H2 production using microbial consortia or non-sterile conditions. Sulfate reducing bacteria were found in anaerobic starch-hydrolyzing consortium and their inhibitory effect on the following H2 photoproduction by purple nonsulfur bacteria was shown. This inhibition was clearly demonstrated in the mixed culture of Rhodobacter sphaeroides and Desulfomicrobium baculatum using the synthetic medium. This effect was conditioned by sulfide production rather than H2 consumption or competition for organic substrate. Actually, the addition of equivalent sulfide concentration brought about the similar effects: inhibition of H2 production without growth inhibition, cells aggregation, and the increase of carbohydrate content as an alternative way of expenditure of organic acids. In the long-term experiments the average sulfide concentration of about 0.3 mM was detrimental while in short-terms the H2 production was not inhibited even at 3.2 mM. The protective effect of molybdates against sulfate reducers and sulfide was discussed.