Effect of growth conditions on advantages of hup− strain for H2 photoproduction by Rubrivivax gelatinosus

H2 photoproduction by growing cultures of hup− mutant and parental strain RL2 of Rubrivivax gelatinosus was compared. We checked the influence of different substrates, presence of air and N2, culture shaking, inoculum concentrations. At low inoculum concentration, hup− strain demonstrated significant advantage over the parental strain in microaerobic conditions, while under N2-Ar atmosphere it was lower and vanished in anaerobic conditions (Ar only). This advantage was evident when using substrates with low degree of reduction (malate and succinate). Culture shaking under microaerobic conditions and in presence of N2 completely prevented H2 production by both strains. The high inoculum concentration inhibited H2 production under microaerobic conditions and in presence of N2, unlike to anaerobic conditions. With inoculum concentration increase, H2 production decreased not gradually but stepwise which means some metabolic shift. H2 production by hup− strain seems to be more tolerant to air traces than by parental strain.