The influence of recent growth history on the phenotype of Escherichia coli.

Abstract

Escherichia coli, strain 300U, was grown for 450 generations in 6 different media. Each line was then subcultured into each of the 6 media, and allowed to grow for about 12 generations. The growth rates and rates of induced β-galactosidase synthesis were, as expected, highly dependent on the medium in which the cells were growing at the time of sampling. Both parameters, and particularly β-galactosidase synthesis, also showed some influence of the medium in which the cells had previously been grown. Of 26 soluble protein components separated by gel electrophoresis in the same experiment, 9 were highly dependent on the current medium, with insignificant effects of the previous growth conditions; 4 were significantly affected by the previous medium but were not influenced by the current medium; 3 were influenced both by current and earlier growth conditions; and 10 components showed no variation. In further experiments, the kinetics of labelled phenylalanine incorporation into soluble proteins were studied by pulse-labelling during growth upshifts and downshifts. The responses of the various protein components to the growth shift were kinetically variable; some responded immediately while in others the response was delayed. In other cases, a series of oscillations were observed after an initial response, while a final category showed little response to the growth shift. The proportional incorporation of phenylalanine into the different bands was still changing 1–2 generations after the shift. It is concluded that a period of adaptation of at least 12 generations is required for cells to reach a new equilibrium after a growth shift.