Hydrogen Metabolism By A Marine Blue-Green Alga, Oscillatoria Sp Miami Bg 7

When a combined nitrogen sufficient culture was inoculated into a nitrogen limited medium, cellular contents of chlorophyll and protein decreased whereas carbohydrate content increased during the culture period. Accompanying the changes in cellular composition, the oxygen photoproduction capability decreased and hydrogen photoproduction capability increased dramatically. The maximum rate of hydrogen photoproduction was 260 (mu)moles/ mg chl a/ hr. The principal enzyme responsible for hydrogen photoproduction was nitrogenase. The large accumulation of carbohydrate consisted of a glucose polymer (glycogen) which amounted to 50 to 60 % of dry weight. During anaerobic illumination of nitrogen limited BG 7 culture, a complete conversion from glycogen and water to hydrogen and carbon dixoide took place. Light driven cyclic photophosphorylation contributed to the ATP (adenosine 5\u27-triphosphate) supply required for the nitrogenase catalysis.Enhanced hydrogen photoproduction by combined nitrogen limited culture was apparently related to: (i) an increase in nitrogenase synthesis, (ii) accumulation of an electron donor compound (glycogen) and (iii) reduction of photosystem II activity. A stable accumulation of hydrogen gas was thus obtained via a temporal separation of electron donor accumulation phase (photosynthesis) and hydrogen photoproduction phase.A unique feature with respect to hydrogen production by strain BG 7 was the stable accumulation of hydrogen gas in the flasks without any special treatments. This was related to the lack of hydrogen uptake activity in this strain. These results indicate that strain BG 7 has favorable characteristics for future application to seawater based biosolar hydrogen production