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Progressively increasing the input concentration of growth-limiting nutrient (glucose, ammonia, K+) to anaerobic chemostat cultures ofKlebsiella aerogenes(D=0.38 h−1; 35°C; pH 6.8) led to a non-linear increase in bacterial cell concentration. At modest population densities, residual growth-limiting substrate levels increased substantially, with increasing input concentration, and the culture bacterial dry weight tended to a constant value. With the glucose-limited culture, increasing the glucose input concentration above 20 g·1−1led to accumulation of unused glucose and a change in the fermentation pattern. There was a concomitant lowering of the yield value with respect to glucose consumption, and the calculated YATPvalue similarly declined. Addition of extra essential (non-limiting) nutrients to the culture was without effect. Similarly, addition of individual fermentation products (acetate, ethanol,d-lactate, 2,3-butanediol, succinate) to the feed medium, in varying concentrations and in different combinations, failed to influence the fermentation pattern or the energetics of cell synthesis. However, a clear correlation was observed between the yield values (of both glucose- and K+-limited cultures) and the steady state concentration of CO2in the effluent gas. Increasing the concentration CO2either by increasing the population density or lowering the sparging rate of nitrogen gas through the culture, effected a lowering of the yield values. It is suggested that dissolved CO2exerts an effect on both metabolism and the energetics of cell synthesis. A possible mechanism of energy dissipation (i.e., a futile cycle) involving carboxylation and decarboxylation reactions is proposed.

1. Mg2+-limited Bacillus subtilis var. niger, growing in a chemostat in a simple salts medium, contained considerably more potassium and phosphorus than Mg2+-limited Aerobacter aerogenes growing in a similar medium at corresponding dilution rates. 2. Growth of the bacillus in a K+-limited environment did not lower the cellular potassium and phosphorus contents, the molar proportions of cell-bound magnesium, potassium, RNA (as nucleotide) and phosphorus being approximately constant at 1:13:5:13 (compared with 1:4:5:8 in Mg2+-limited or K+-limited A. aerogenes). 3. Growth of B. subtilis in a phosphate-limited environment caused the cellular phosphorus content to be lowered to a value similar to that of Mg2+-limited A. aerogenes, but the potassium content was not correspondingly lowered; the molar potassium:magnesium ratio varied from 14 to 17 with changes in dilution rate from 0·4 to 0·1hr.−1. 4. Whereas over 70% of the cell-bound phosphorus of Mg2+-limited or K+-limited A. aerogenes was contained in the nucleic acids, these polymers accounted for less than 50% of the phosphorus present in similarly limited B. subtilis; much phosphorus was present in the walls of the bacilli, bound in a teichoic acid-type compound composed of glycerol phosphate and glucose (but no alanine). 5. Phosphate-limited B. subtilis cell walls (from organisms grown at a dilution rate of 0·2hr.−1) contained little phosphorus and no detectable amounts of teichoic acid, but 40% of the cell-wall dry weight could be accounted for by a teichuronic acid-type compound; this contained a glucuronic acid and galactosamine, neither of which could be detected in the walls of Mg2+-limited B. subtilis grown at a corresponding rate. 6. It is suggested that the high concentration of potassium in growing B. subtilis (compared with A. aerogenes) results from the presence of large amounts of anionic polymer (teichoic acid or teichuronic acid) in the bacillus cell walls.

1. Quantitative determination of the anionic polymers present in the walls of Bacillus subtilis var. niger organisms undergoing transition, in a chemostat culture, from either Mg2+-limitation to PO43−-limitation or K+-limitation to PO43−-limitation showed that teichuronic acid synthesis started immediately the culture became PO43−-limited and proceeded at a rate substantially faster than the rate of biomass synthesis. 2. Simultaneously, the cell-wall teichoic acid content diminished at a rate greater than that due to dilution by newly synthesized wall material, and fragments of teichoic acid and mucopeptide accumulated in the culture extracellular fluid. 3. Equally rapid reverse changes occurred when a PO43−-limited B. subtilis var. niger culture was returned to being Mg2+-limited. 4. It is concluded that in this organism both teichoic acid and teichuronic acid syntheses are expressions of a single genotype, and a mechanism for the control of synthesis of both polymers is suggested. 5. These results are discussed with reference to the constantly changing environmental conditions that obtain in a batch culture and the variation in bacterial cell-wall composition that is reported to occur throughout the growth cycle.