Physiological factors determining hydrogenase activity in nitrogen-fixing heterocystous cyanobacteria.

Four species of nitrogen-fixing heterocystous cyanobacteria were compared with respect to induction of hydrogenase activity. Two of the strains contained phycoerythrin and built up high levels of carbohydrate storage material when grown in batch culture under nitrogen-fixing conditions and continuous illumination. These strains did not exhibit hydrogenase activity. Lack of activity in the phycoerythrin-containing species was determined by cell-free assays measuring both hydrogen-evolving and hydrogen-uptake activities. Apparently, expression of hydrogenase is negatively correlated with the carbohydrate pool present and concurrent respiration. Furthermore, there is an apparent relationship between the presence of phycoerythrin, carbohydrate accumulation, and the absence of hydrogenase activity.