THE QUANTUM REQUIREMENT FOR H-2 PRODUCTION BY ANOXYGENIC PHOTOTROPHICBACTERIA

Cultures from three groups of phototrophic bacteria (green sulphur bac teria, purple non-sulphur bacteria and purple sulphur bacteria) were i nvestigated in respect of the quantum requirement for H-2 production ( Q(H2)). Rates of H-2 formation were determined by means of a Clark-typ e H-2 electrode with dense suspensions of whole cells and malate, acet ate or sulphide as electron donor. At low light intensities (0-3 W.m-2 of monochromatic light) the minimum quantum requirement was 8.6 quant a per H-2 with Chlorobium vibrio-forme, 7.5 with Rhodospirillum rubrum , and 23.2 with Ectothiorhodospira shaposhnikovii. The physiological e fficiency, defined as the measured Q(H2) compared to the theoretical v alue calculated from the energy requirement of the physiological proce sses involved, was 94%, 88%, or 28%, respectively. With increasing lig ht intensities the quantum requirement also increased. Various hydroge nase inhibitors either inhibited both H-2 uptake and production (Cu2+, NO), or affected neither of these activities (CO, C2H2, N2O, ethylene dinitrilotetraacetate). An uptake hydrogenase-deficient Hup--mutant of R. rubrum had higher rates of net H-2 production but a similar quantu m requirement. The energetic efficiency of H-2 production by various b iological and artificial systems is discussed.