Envelope protein synthesis and inhibition of cell division in Escherichia coli during inactivation of the B subunit of DNA gyrase.

The rates of synthesis of inner and outer membrane proteins of Escherichia coli K12 during inhibition of cell division have been studied. When cell division was inhibited, either by treatment of wild-type cells with the antibiotic clorobiocin (an inhibitor of the B subunit of DNA gyrase) or by a temperature shift of a gyrB-ts mutant, a 40% reduction in the rate of synthesis of total outer membrane protein relative to that of the inner membrane was observed. When a gyrB-ts mutant was shifted to high temperature under conditions which allowed continued cell division, this large reduction in the rate of synthesis of outer membrane protein relative to inner membrane protein was not observed. In contrast to the results obtained with clorobiocin, inhibition of cell division by the beta-lactam antibiotic cefuroxime did not cause any detectable disturbance in the rate of synthesis of either inner or outer membrane protein. This demonstrates that inhibition of septum formation per se does not perturb synthesis of envelope protein. The data obtained are consistent with a model in which the rate of synthesis and therefore expansion of outer membrane is one of many conditions which must be satisfied before septum formation can occur. The results are discussed in relation to such a model, and to previous findings which have shown that the rate of synthesis of outer membrane proteins displays a linear mode with an abrupt doubling in rate at a discrete point in the cell cycle.