Quantitative Analysis of Potassium Ion Pool in Escherichia coli K-12

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Properties of the K⁺ pool of Escherichia coli K-12 and its roles in the bacterial growth were studied quantitatively. Cells are able to maintain 240mM K⁺ in the pool irrespective of K⁺ concentrations in the medium and against a concentration gradient of more than 5 orders of magnitude. The amount of K⁺ in the pool strictly determines the rate of growth and growth yield. Cells cease to grow when the K⁺ concentration in the pool is down to about 25mM. Rb⁺ is not able to substitute for K+ in the K⁺ pool completely and the rates of growth of cells become slower when more of the K⁺ in the pool is replaced by Rb⁺ Most K⁺ in the pool exists in an osmotically active form but 10 to 20% of the K⁺ is resistant to changes in osmolarity and temperature of the medium and maintained in the cells depending on the supply of endogenous metabolic energy.
Two constitutive transport systems for K⁺ were shown to be functioning in the establishment of the K⁺ pool. A high affinity system seems to relate mainly to the establishment of steady state of the K⁺ pool. A low affinity system with a high V_max catalyzes the rapid influx of K⁺ when the cells are exposed to changes in temperature and osmotic conditions. This system shares Rb⁺ as a common substrate and is driven by both ATP and a proton motive force.