Biophysics Research Division and Department of Biological Chemistry, University of Michigan, Ann Arbor, MI 48109, USA.
Bacterial adaptation to nutrient limitation and increased population densities is central to survival and virulence. Surprisingly, <3% of Escherichia coli genes are known to play roles specific to the stationary phase. There is evidence that the leucine-responsive regulatory protein (Lrp) may play an important role in stationary phase, so this study used microarrays representing >98% of E. coli genes to more comprehensively identify those controlled by Lrp. The primary analysis compared isogenic Lrp(+) and Lrp(-) strains in cells growing in steady state in glucose minimal medium, either in the presence or absence of leucine. More than 400 genes were significantly Lrp-responsive under the conditions used. Transcription of 147 genes was lower in Lrp(+) than in Lrp(-) cells whether or not leucine was present; most of these genes were tightly coregulated under several conditions, including a burst of synthesis on transition to stationary phase. This cluster includes 56 of 115 genes already known to play roles in stationary phase. Our results suggest that the actual number of genes induced on entrance into stationary phase is closer to 200 and that Lrp affects nearly three-quarters of them, including genes involved in response to nutrient limitation, high concentrations of organic acids, and osmotic stress.