Magnesium-limited growth of Aerobacter aerogenes in a chemostat

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Abstract
The influence of Mg2+-limitation, com-pared with carbon-limitation, on bacterial concentration, and on protein, carbohydrate, RNA and DNA contents of A. aerogenes cultures (grown in the chemostat at several dilution rates) was determined. In both types of culture the bacterial protein, carbohydrate and DNA contents varied slightly, and the RNA content grossly, with changes in dilution rate. Bacterial yield varied with growth rate, and to a marked degree in the Mg2+-limited culture; this resulted from Mg2+ control of RNA synthesis. A growth-rate independent stoichiometry between RNA and Mg2+ was observed; 4 moles of RNA nucleotide were synthesized per mole of Mg2+ present in the culture. The protein and RNA distributions between cellular components varied with growth rate. The ribosomal fractions increased with increasing growth rate, as did the RNA: protein ratios in these fractions, in both cultures. Mg2+-limited bacteria contained little polysaccharide; washed suspensions of such organisms synthesized polysaccharide from glycerol at a low rate as compared with C-limited bacteria. Added Mg2+ stimulated polysaccharide synthesis by Mg2+-limited bacteria but not by C-limited bacteria. Washed suspensions of bacteria were induced to synthesize [beta]-galactosidase. With cultures grown at three different dilution rates, the rates of enzyme synthesis in C-limited bacteria were twice those found with Mg2+-limited bacteria, though both had equal ribosome contents.