Molecular physiology of the dynamic regulation of carbon catabolite repression in Escherichia coli.

We report on the use of the chemostat as an optimal device to create time-invariant conditions that allow accurate sampling for various omics assays in Escherichia coli, in combination with recording of the dynamics of the physiological transition in the organism under study that accompany the initiation of glucose repression. E. coli cells respond to the addition of glucose not only with the well-known transcriptional response, as was revealed through quantitative PCR analysis of the transcript levels of key genes from the CRP (cAMP receptor protein) regulon, but also with an increased growth rate and a transient decrease in the efficiency of its aerobic catabolism. Less than half of a doubling time is required for the organism to recover to maximal values of growth rate and efficiency. Furthermore, calculations based on our results show that the specific glucose uptake rate (q(S)) and the H+/e(-) ratio increase proportionally, up to a growth rate of 0.4 h(-1), whilst biomass yield on glucose (Y-xls) drops during the first 15 min, followed by a gradual recovery. Surprisingly, the growth yields after the recovery phase show values even higher than the maximum theoretical yield. Possible explanations for these high yields are discussed.