Leucine-Responsive Regulatory Protein-Mediated Repression of clp (Encoding CS31A) Expression by l-Leucine and l-Alanine in Escherichia coli

CS31A produced by septicemic and diarrheic Escherichia coli belongs to the Pap-regulatory family of adhesive factors, which are under methylation-dependent transcriptional regulation. Common features of operons encoding members of this family include two conserved GATC sites in the upstream regulatory region, and transcriptional regulators homologue to the PapB and PapI proteins. Methylation protection of GATC sites was previously shown to be dependent on the leucine-responsive regulatory protein (Lrp). Lrp and ClpB, the PapB equivalent, repressed clp basal transcription. A PapI homologue (AfaF) was required together with Lrp to establish the phase variation control, which gave rise to phase-ON cells that expressed CS31A and phase-OFF cells that did not express CS31A. In phase-OFF cells, the GATC(dist) site was methylated and the GATC(prox) site was protected from methylation, whereas in phase-ON cells, the inverse situation was found. Unlike Pap fimbriae, CS31A synthesis was dramatically reduced in media containing l-alanine or l-leucine. l-Alanine prevented the OFF-to-ON switch, locking clp expression in the OFF phase, whereas l-leucine repressed transcription without obvious effect on the switch frequency of phase variation. In phase-variable cells, leucine and alanine promoted methylation of GATC(dist) and methylation protection of GATC(prox), increasing the methylation pattern characteristic of repressed cells. Furthermore, alanine prevented the AfaF-dependent methylation protection of GATC(dist) and thus the appearance of phase-ON cells. In addition, analysis of clp expression in a Lrp-negative background indicated that alanine and leucine also repressed clp transcription by a methylation-independent mechanism

Ethanolamine catabolism by Escherichia coli commensal strains.

International audienc

Design and validation of a dual-fluorescence reporter system to monitor bacterial gene expression in situ

International audienc

Diversity of ethanolamine utilization by human commensal Escherichia coli

International audienc

Role of nitric oxide in the outcome of EHEC infections

National audienc

Ethanolamine catabolism by Escherichia coli commensal strains

International audienc

Pushing the limits of STEC molecular risk assessment: identification of genes specifically induced in vivo as potential new genetic biomarkers

National audienceEpidemiologic studies reveal that only few virulence factors are frequently associated with Shiga toxin-producing Escherichia coli (STEC) strains that cause severe disease in humans. Among them, Shiga toxins (Stx) is required for the development of the most severe symptoms in STEC infected patients but is not strictly sufficient to make an E. coli strain pathogenic to human. Indeed, many STEC strains isolated from rearing animals have never been implicated in human disease. It therefore appears crucial to increase our knowledge on STEC pathogenesis at the molecular level. We developed a RIVET (Recombination-based in vivo expression technology) strategy in order to identify STEC genes specifically induced in vivo during mouse infection. Construction and screening of a RIVET promoter library from the typical STEC O157:H7 strain EDL933 resulted in the identification of 31 in vivo induced (ivi) genes. Most but not all, have an attributed function and are involved in either metabolism or stress response pathways, indicating that STEC has to adapt to the intestinal ecosystem. Additionally, some identified ivi genes belong to the dispensable genome of E. coli and analysis of their distribution among E. coli strains revealed a strong prevalence for some of them specifically in STEC strains. We also observed correlations between ivi genes and virulence genes, serotypes and/or seropathotypes. Finally, we assessed their contribution to STEC pathogenesis by infecting mice with mutants inactivated for selected ivi genes. This work may thus help to improve STEC molecular risk assessment schemes by giving new insights into molecular aspects of STEC pathogenesis

Ethanolamine catabolism by Escherichia coli commensal strains

International audienc

Design and validation of a dual-fluorescence reporter system to monitor bacterial gene expression in situ

International audienc

Design and validation of a dual-fluorescence reporter system to monitor bacterial gene expression in situ

International audienc