Murein chemistry of cell division in Escherichia coli

The length distribution of the glycan strands of murein has been analysed with a novel method in filamentous and spherical cells of Escherichia coli, as well as during septum formation and cell separation. A shift to the longer glycan strands was observed in the murein of furazlocillin-induced filaments. In contrast, shorter glycan strands were increased in the murein of mecillinam-induced spherical cells. During septum formation in a chain-forming envA mutant that is defective in the splitting process of the septum, a shift to the shorter glycan strands was detected that was not seen in wild type E. coli cells. It is concluded that septum-specific murein structures of rather short glycan strands are released during splitting of the septum. This intermediate material remains present in the septum of the envA mutant. The splitting process of the septum was investigated by analysing the murein during penicillin-induced bacteriolysis, which is known to take place by strictly localized murein degradation in the equatorial zone of the cell. No changes in the length distribution of the glycan strands could be detected during penicillin-induced lysis, with the exception of an increase in disaccharides, the shortest glycan strands possible. This is explained by the action of exo-muramidases progressively digesting glycan strands, leaving disaccharide units covalently linked to the remaining murein at the sites of murein cross-linkage. It is proposed that this "zipper-like" mechanism represents the normal cutting process of the septum during cell separation.