Effect of growth conditions on peptidoglycan content and cytoplasmic steps of its biosynthesis in Escherichia coli

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Abstract
In an attempt to bring some insight into how peptidoglycan synthesis is controlled in Escherichia coli, simple parameters, such as cell peptidoglycan content, the pool levels of its seven uridine nucleotide precursors, and the specific activities of five enzymes involved in their formation, were investigated under different growth conditions. When exponential-phase cells with generation times ranging from 25 to 190 min were examined, the peptidoglycan content apparently varied as the cell surface area changed, and no important variations in the pool levels of the nucleotide precursors or in the specific activities of the five enzymes considered were observed. The peptidoglycan of exponential-phase cells accounted for 0.7 to 0.8% of the dry cell weight, whereas that of stationary-phase cells accounted for 1.4 to 1.9%. Depending on the growth conditions, the number of peptidoglycan disaccharide peptide units per cell varied from 2.4 X 10(6) to 5.6 X 10(6). The levels of the nucleotide precursor pools as well as the specific activities of the D-glutamic acid- and D-alanyl-D-alanine-adding enzymes varied little with the growth phase. The specific activities of UDP-N-acetylglucosamine transferase, UDP-N-acetylglucosamine-enolpyruvate reductase, and the diaminopimelic acid-adding enzymes decreased by 20 to 50% at most in the late stationary phase. The results are discussed in terms of the possible importance for cell survival of the maintenance of a high capacity for peptidoglycan synthesis, whatever its rate under various growth conditions, and of a balance between the synthesis and breakdown of peptidoglycan during active growth.