초록
Photoproduction of H<SUB>2</SUB> gas has been examined in sulfur/phosphorus-deprived Chalmydomonas reinhardtii cultures, placed in photobioreactors (PhBRs) with different gas phase to liquid phase ratios (V<SUB>g.p.</SUB>/V<SUB>l.p.</SUB>). The results demonstrate that an increase in the ratio stimulates H<SUB>2</SUB> photoproduction activity in both algal suspension cultures and in algae entrapped in thin alginate films. In suspension cultures, a 4x increase (from ∼0.5 to ∼2) in V<SUB>g.p.</SUB>/V<SUB>l.p</SUB> results in a 2x increase (from 10.8 to 23.1 mmol l<SUP>-1</SUP> or 264-565 ml l<SUP>-1</SUP>) in the total yield of H<SUB>2</SUB> gas. Remarkably, 565 ml of H<SUB>2</SUB> gas per liter of the suspension culture is the highest yield ever reported for a wild-type strain in a time period of less than 190 h. In immobilized algae, where diffusion of H<SUB>2</SUB> from the medium to the PhBR gas phase is not affected by mixing, the maximum rate and yield of H<SUB>2</SUB> photoproduction occur in PhBRs with V<SUB>g.p.</SUB>/V<SUB>l.p</SUB> above 7 or in a PhBR with smaller headspace, if the H<SUB>2</SUB> is effectively removed from the medium by continuous flushing of the headspace with argon. These experiments in combination with studies of the direct inhibitory effect of high H<SUB>2</SUB> concentrations in the PhBR headspace on H<SUB>2</SUB> photoproduction activity in algal cultures clearly show that H<SUB>2</SUB> photoproduction in algae depends significantly on the partial pressure of H<SUB>2</SUB> (not O<SUB>2</SUB> as previously thought) in the PhBR gas phase.