Cell division in a chain-forming envA mutant of Escherichia coli K12. Fine structure of division sites and effects of EDTA, lysozyme and ampicillin.

A chain-forming mutant of Escherichia coli K12 has recently been described which exhibits a decreased tolerance to ampicillin, rifampicin, actinomycin D, and several other antibacterial agents {Normark et al. 1969, Normark 1970). The mutated gene responsible for chain formation and drug sensitivity, denoted envA, was mapped at 1.5 min {Normark 1970). In this paper the cell division process in the envA mutant and its wild type parental strain is investigated. Electron microscopy revealed that all layers of the cell envelope participate in the invagination process during cell “division in the wild type strain. In contrast, in the chain forming envA mutant, a septum was constantly formed at the site of division which separated individual cell units. The septum was delimited by the plasma membrane and was composed of periplasm and a central septal structure which by its sensitivity to lysozyme was identified as the murein skeleton. Plasmolysis of chains by 30 per cent sucrose caused a significant broadening of the septal regions, but left the murein layer intact. Ampicillin was without effect on the septal murein component. Sites at which the cytoplasmic membrane was attached to the cell wall were frequently observed in close relation to the invagination areas, even after removal of the murein layer by lysozyme. Inhibition of DNA and murein synthesis did not affect the ability of chains to be transformed into separate cells. Protein synthesis however, was a prerequisite for cell separations. It is suggested that the envA gene mediates a defect in the association of the murein skeleton with the outer layers of the envelope. Models for septum formation are presented.