EFFICIENT HYDROGEN PHOTOPRODUCTION BY SYNCHRONOUSLY GROWN CELLS OF A MARINE CYANOBACTERIUM, SYNECHOCOCCUS SP MIAMI BG-043511, UNDER HIGH CELL-DENSITY CONDITIONS

The capability of hydrogen photoproduction under high cell density conditions was examined using synchronously grown cells of nitrogen-fixing Synechococcus sp. Miami BG 043511. Optimum hydrogen yield was obtained when vessels (25 mL) contained 0.2 to 0.3 mg chlorophyll a in 3-mL cell suspension. During a 24-h incubation period, an initial phase of hydrogen and carbon dioxide production and a subsequent phase of carbon dioxide uptake and oxygen production were observed; hence, hydrogen and oxygen accumulated as major products after 24 h. After the initial 24-h incubation, as high as 7.4 and 3.7 mL (at standard condition) of hydrogen and oxygen, respectively, accumulated in vessels with 22-mL gas phase. This indicated that the pressure in the flask increased to 1.5 atmosphere. Energy conversion efficiency based on photosynthetically active radiation (25 W/m(2)) was about 2.6%. However, increased pressure somehow reduced the duration of hydrogen production. Duration of hydrogen and oxygen production was prolonged by periodical (24-h interval) gas replacement during incubation. (C) 1994 John Wiley & Sons, Inc.