Regulation of murein biosynthesis and septum formation in filamentous cells of Escherichia coli PAT 84.

Both the beta-lactam antibiotic, cephalexin, and the deoxyribonucleic acid synthesis inhibitor, nalidixic acid, are known to inhibit cell division in Escherichia coli and induce the formation of filaments. The biosynthesis of murein was investigated in these filaments and compared with the murein synthesized by the normally dividing rods of E. coli PAT 84. Differences were found in the extent of peptide side-chain cross-linkage. Filamentous cells had higher extents of cross-linkages in their newly synthesized murein. Quantitative analyses of the D-alanine carboxypeptidase and transpeptidase reactions in the different cells revealed that the carboxypeptidase activity of the filamentous cells was partially inhibited. These results were similar to those previously found with filaments that were obtained after growth of the thermosensitive division mutant at its restrictive temperature. We conclude that the formation of new cell ends (septa) depends on the proper balance between the activities of the D-alanine carboxypeptidase that regulates the availability of precursor doners and the transpeptidase, which catalyzes cross-linking and attachment of newly synthesized murein.