Studies on the physiology of heterocyst production in the nitrogen-fixing blue-green alga Anabaena sp. L-31 in continuous culture

Abstract

Induction of heterocysts in the blue-green alga Anabaena sp. L-31 is totally inhibited by potassium nitrate in batch cultures whereas in continuous cultures no inhibition is observed at high dilution rates. When nitrate is utilized ammonia accumulates in the growth medium, the quantity of extracellular ammonia declining with increasing dilution rate. The rate of release of ammonia per cell increases with decreasing density of organisms, and induction of heterocysts is consistently observed when ammonia release per cell exceeds 2 x 10^-10 µg. It is inferred that such excessive release depletes the level of intracellular ammonia causing the induction of heterocysts.