The utilization of potassium by Bact. lactis aerogenes

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Abstract
As the potassium-ion concentration of synthetic media is decreased the total population ( n s ) of Bact. lactis aerogenes which they support tends towards zero. Added potassium gives nearly linear increases in n s . The use of the radioactive isotope shows that the cells take up nearly all the potassium from the medium over wide ranges of concentration. Sodium cannot replace potassium, and the use of the active isotope shows that it is probably not taken up by the cells. Rubidium replaces potassium with about quarter efficiency, but lithium and caesium have only very small effects. The potassium appears to play the part of an enzyme-activator, and in glucose-ammonium sulphate media is displaced by the acid formed during growth. A quantitative treatment of the competition between K + and H + for an array of negative sites on an enzyme surface is attempted. On the assumption that a certain critical area of K + -activated sites is necessary for growth to continue, a relationship between n s and the [K + ] is developed and shown to be in general agreement with the experimental facts. The relation between n s and potassium concentration varies from one medium to another. In glycerol-ammonium sulphate media, where n s is insensitive to the initial pH, the amounts of potassium present in the ammonium or sodium salts of the buffer support considerably greater populations than they can in the glucose medium. Further increases, however, demand much greater potassium concentrations, the results being in accord with the view that other products formed in the glycerol medium can displace potassium from the relevant enzyme and limit growth.

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