Summary: When nickel-depleted cells of with nitrogenase repressed by growth on ammonia or into late stationary phase) were used to re-initiate nitrogen-fixing growth in fresh nickel-depleted medium a pronounced growth lag was observed. The growth lag was not observed in the presence of NiSO (0.68 μ). It was associated with delayed heterocyst differentiation, delayed nitrogenase synthesis and inhibition of pigment synthesis. During the lag a pronounced but transient accumulation of cyanophycin was observed, followed by an accumulation of urea in the growth medium. It is proposed that nickel depletion results in a diversion of ammonia from protein synthesis into cyanophycin, thereby delaying the synthesis of proteins and enzymes required for the synthesis of active nitrogenase.


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