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Abstract
SUMMARY: The growth of Aerobacter aerogenes 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+, Mg2+, RNA and phosphorus contents increased as the ‘steady-state’ growth rate was increased. The yield variation was similar to that observed when either Mg2+ or PO4 3- was the limiting component of the medium. Analysis of K+-limited organisms revealed a molar stoichiometry between cellular Mg2+, K+ and P (close to 1:4:8, respectively) that was almost independent of growth rate. It is suggested that a precise intracellular K+:Mg2+ 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 A. aerogenes 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 A. aerogenes suspensions in phosphate saline (pH 6.5) was a function of their ‘steady-state’ growth rate.
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