Requirement of low oxidation-reduction potential for photosynthesis in a blue-green alga (Phormidium sp.)

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Abstract
Photosynthesis in a Phormidium species which forms dense conical-shaped structures in thermal springs is strongly inhibited by aeration but is stimulated by sulfide and other agents (cysteine, thioglycolate, sulfite) which lower the oxidation-reduction potential. The compact structures which this alga forms in nature may restrict oxygen penetration from the environment so that the anaerobic or microaerophilic conditions necessary for photosynthesis can develop. The alga may be defective in a regulatory mechanism that controls the reoxidation of reduced pyridine nucleotides formed during photosynthesis. It is suggested that other mat-forming and benthic blue-green algae may also prefer anaerobic conditions for growth and photosynthesis.