SUMMARY: The growth of cultures in a chemostat under conditions of K-limitation was investigated. At a fixed dilution rate there was a linear relationship between bacterial concentration and the K concentration in the culture. The extrapolated plot did not pass through the origin, however; this indicated the presence in the medium of substance(s) supporting some growth in the absence of K. The growth yield varied markedly with the dilution rate; bacterial concentration decreased and the cellular K, Mg, RNA and phosphorus contents increased as the ‘steady-state’ growth rate was increased. The yield variation was similar to that observed when either Mg or PO was the limiting component of the medium. Analysis of K-limited organisms revealed a molar stoichiometry between cellular Mg, K and P (close to 1:4:8, respectively) that was almost independent of growth rate. It is suggested that a precise intracellular K:Mg ratio may be of importance for maintaining ribosomal structures in a suitable functional configuration or degree of aggregation, and it is for this purpose that high concentrations of K are present in growing bacteria. K-limited cultures oxidized glycerol rapidly, as did washed supensions of these organisms in phosphate buffer (pH 6.5). Glycerol (10 mM) accelerated the death-rate of K-limited bacteria; potassium (15 mM) and magnesium (15 mM) each decreased this glycerol toxicity and, when added together, abolished it. The death-rate of washed K-limited suspensions in phosphate saline (pH 6.5) was a function of their ‘steady-state’ growth rate.


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