Summary: Cyanophycin, the nitrogen reserve compound in cyanobacteria, has a dynamic metabolism during transitions between the metabolic states of nitrogen deficiency and nitrogen repletion and vice versa. Cyanophycin was transiently synthesized when ammonia-grown or 6308 consumed a limited amount of ammonia. It was synthesized during the phase of declining ammonia concentration, and its degradation was complete by the time the external ammonia had been completely consumed. When nitrogen-starved cells of or 6308 were given a usable source of fixed nitrogen, cyanophycin again accumulated transiently. This synthesis of cyanophycin was triggered by the suddenly renewed availability of fixed nitrogen, and not by the subsequent decline in the external concentration of fixed nitrogen. The cyanophycin was degraded when balanced exponential growth was again possible. Transient accumulations of cyanophycin with similar kinetics were also observed when ammonia was added to nitrogen-fixing It is suggested that cyanophycin serves as a dynamic reservoir which separates the environmental supply of fixed nitrogen from the metabolic demands of the cells, and that this provides a mechanism which enables cyanobacteria to maximize their share of any available fixed nitrogen. This would give cyanobacteria a competitive advantage over other organisms.


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