Effect of sodium on nitrogen fixation in Anabaena torulosa and Plectonema boryanum

Abstract

The cyanobacterium Anabaena torulosa required sodium and molybdenum for nitrogenase activity and diazotrophic growth. Addition of sodium or molybdenum to cultures deficient in either element restored nitrogenase activity. Heterocyst differentiation was unaffected by sodium but molybdenum deficiency enhanced differentiation. The non-heterocystous cyanobacterium Plectonema boryanum 594 also required sodium for nitrogenase activity but synthesized presumptive nitrogenase component I and II proteins during sodium deficiency. The results show that in cyanobacteria nitrogenase is synthesized even in the absence of sodium but functions only in its presence.