Regulation of the intracellular potassium concentration in Escherichia coli B 525

The mutant Escherichia coli B 525 requires histidine, leucine and methionine and an elevated extracellular K⁺ concentration for growth, and is unable to retain K⁺ tightly inside the cells when incubated in media supplemented with glucose, arabinose, galactose or lactose as the sole energy and carbon source. The loss of K⁺ from the cells of B 525 can be prevented by adding histidine and leucine, which react specifically and only in combination. In media supplemented with glycerol as the substrate, with glucose and NH₄⁺, or with glucose under anaerobic conditions, a stationary level of K⁺ inside the cells can be obtained without the addition of histidine-leucine.On the addition of ribose to glycerol-adapted cells of B 525 preincubated in glycerol media, the intracellular K⁺ decreased immediately and markedly. This decrease can be overcome by the addition of histidine-leucine.