Comparative studies on intracellular potassium- and sodium concentrations of wild-type and a macrotetrolide negative mutant of Streptomyces griseus.

Most living cells require potassium for growth and maintain a high intracellular concentration of that ion over a wide range of extracellular concen­ tration. The selectivity for potassium over sodium is determined by the transport systems which reside in the cytoplasmic membrane. It is a well established fact by now that the per­ meability of natural and artifical membranes for potassium is increased by antibiotics such as valinomycin, the macrotetrolides, the gramicidines, and enniatines1_3. This information has led to the hypothesis that ionophores are components of the physiological potassium transport systems4) 5, re­ sponsible for cation selectivity for entry into the cell. I f this view is correct, strains which do not produce such ionophores should have lost the speci­ ficity for potassium. Furthermore, potassium trans­ port should be inhibited by sodium. In a previous paper6 a mutant was described producing no de­ tectable amounts of macrotetrolides, while the parent strain ( Streptomyces griseus T iilO ; ETH 7796) produces several grams of these ionophores per liter under optimal conditions7. We were able to show, that growth of this mutant is inhibited by sodium in media with low extracellular potassium. This inhibition can be restored by adding back potassium. The experiments described in this paper constitute an attempt to analyse if this difference between wild type and mutant can be due to an un-