Quantitative Analysis of Potassium Ion Pool in Escherichia coli K-121

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Abstract
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 240 mM K+ in the pooi 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 25 mM 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 Vmax 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.

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