Pleiotropic effects of potassium deficiency in a heterocystous, nitrogen-fixing cyanobacterium, Anabaena torulosa

Omission of potassium from the growth medium caused multiple metabolic impairments and resulted in cessation of growth of the filamentous, heterocystous, nitrogen-fixing cyanobacterium Anabaena torulosa, during both diazotrophic and nitrogen-supplemented growth. Prominent defects observed during potassium deprivation were: (i) the loss of photosynthetic pigments, (ii) impairment of photosynthetic functions, (iii) reduced synthesis of dinitrogenase reductase (Fe-protein), (iv) inhibition of nitrogenase activity, and (v) specific qualitative modifications of protein synthesis leading to the repression of twelve polypeptides and synthesis and accumulation of nine novel polypeptides. The observed metabolic defects were reversible, and growth arrested under prolonged potassium deficiency was fully restored upon re-addition of potassium. Such pleiotropic effects of potassium deficiency demonstrate that apart from its well-known requirement for pH and turgor homeostasis, K+ plays other vital specific roles in cyanobacterial growth and metabolism.