Metabolic block at early stages of the glycolytic pathway activates the Rcs phosphorelay system via increased synthesis of dTDP-glucose in Escherichia coli

Abstract

A mutational block in the early stages of the glycolytic pathway facilitates the degradation of the ptsG mRNA encoding the major glucose transporter IICBGlc in Escherichia coli. The degradation is RNase E dependent and is correlated with the accumulation of either glucose-6-P or fructose-6-P (Kimata et al., 2001, EMBO J 20: 3587-3595; Morita et al., 2003, J Biol Chem 278: 15608-15614). In this paper, we investigate additional physiological effects resulting from the accumulation of glucose-6-P caused by a mutation in pgi encoding phosphoglucose isomerase, focusing on changes in gene expression. The addition of glucose to the pgi strain caused significant growth inhibition, in particular in the mlc background. Cell growth then gradually resumed as the level of IICBGlc decreased. We found that the transcription of the cps operon, encoding a series of proteins responsible for the synthesis of colanic acid, was markedly but transiently induced under this metabolic stress. Both genetic and biochemical studies revealed that the metabolic stress induces cps transcription by activating the RcsC/YojN/RcsB signal transduction system. Overexpression of glucose-6-P dehydrogenase eliminated both growth inhibition and cps induction by reducing the glucose-6-P level. Mutations in genes responsible for the synthesis of glucose-1-P and/or dTDP-glucose eliminated the activation of the Rcs system by the metabolic stress. Taken together, we conclude that an increased synthesis of dTDP-glucose activates the Rcs phosphorelay system, presumably by affecting the synthesis of oligosaccharides for enterobacterial common antigen and O-antigen.