Characterization and optimization of hydrogen photoproduction by a saltwater blue-green alga, Oscillatoria sp. Miami BG7. I. Enhancement through limiting the supply of nitrogen nutrients

Abstract

Hydrogen photoproduction by a marine, non-heterocystous, filamentous blue-green alga, Oscillatoria sp. Miami BG7 was studied in its relationship to nitrogen nutrients in the culture medium. When a combined nitrogen sufficient culture was inoculated into a combined nitrogen limited medium, cellular content of chlorophyll and protein decreased whereas the carbohydrate content increased significantly during the culture period. Accompanying this change of cellular composition the oxygen photoproduction capability decreased and hydrogen photoproduction capability increased dramatically. The maximum rate of hydrogen photoproduction was 260 μmol/mg chlorophyll/h. Hydrogen production was strictly light dependent under an anaerobic condition. Along with hydrogen photoproduction, carbon dioxide was also produced. The ratio of hydrogen and carbon dioxide photoproduction was approximately two. The mechanism of hydrogen photoproduction enhancement in combined nitrogen limited culture is apparently related to the increase of nitrogenase synthesis, decline of photosystem II activity, and the accumulation of electron donor substances during culture. Another interesting feature of hydrogen production was accumulation of gas in the flasks without any special treatments. This is related to the lack of hydrogen uptake activity in this strain. These results indicate that this strain has favorable characteristics for future application to biosolar fuel production.