Murein and lipopolysaccharide biosynthesis in synchronized cells of Escherichia coli K 12 and the effect of penicillin G, mecillinam and nalidixic acid

The incorporation of radioactive N-acetylglucosamine into murein and lipopolysaccharide of synchronized cells of Escherichia coli K 12 was followed over 100 min in the presence of antibiotics. At 20 min intervals cell walls were prepared. Lipopolysaccharide and murein sacculi were isolated and the radioactivity was quantified in both polymers. Labelled, newly synthesized murein was characterized according to murein subunits linked to lipoprotein, and the degree of crosslinkage. Furthermore, murein subunits containing anhydromuramic acid were determined, permitting the calculation of the average glycan chain length. The results indicated that penicillin G at 30 μg/ml stimulated the incorporation of new murein subunits into sacculi followed by a sudden increase in lipopolysaccharide incorporation into the outer membrane. The degree of crosslinkage in murein synthesized in the presence of 30 μg/ml penicillin G was higher than in the control, and almost twice as high as in murein synthesized in the presence of 20 μg/ml nalidixic acid. Both antibiotics inhibited cell division at the concentrations indicated. Murein synthesized in the presence of 2 μg/ml mecillinam also showed higher crosslinkage. However, about twice as much anhydromuramic acid-containing subunits were observed as in the control. At the same time lipopolysaccharide incorporation into the outer membrane was stimulated two- to three-fold.