Studies on Bacterial Mutability: The Time of Appearance of the Mutant in Escherichia coli

Abstract

An explanation is offered for the delay in the appearance of mutant papillae from parent colonies. The mutants considered are citrate-fermenting E. coli from non-citrate-fermenting cells. The delay is not considered attributable solely to the low rate of mutation nor to the age of the cells. In this system, at least, mutation occurs regularly though rarely and may arise equally from either young or old cells. The time required for mutants to appear is a function of certain environmental conditions. In this instance, the presence or absence of citrate in the medium is one determining factor. Even in a favorable medium, however, the appearance of mutant papillae is delayed. Evidence is adduced that this delay is due to the slow rate of growth of the newly formed mutant cells and further that the slow rate of growth is caused by an unfavorable effect of metabolic products of the parent cells.