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The McbR transcription factor links intracellular folate pool to virulence in enteric pathogens

ABSTRACT: Bacterial pathogens must coordinate the expression of metabolically expensive virulence programs during host colonization. While the impact of environmental cues on virulence has been extensively studied, direct sensing of metabolic intermediates to inform virulence expressions is less understood. Sudden competition with the resident microbiota in the case of an infection is guaranteed to have a massive impact on the bacteria’s central metabolism, which may be used as a cue for the expression of virulence factors. Here, we identify how fluctuations in the intracellular folate pool can affect expression of virulence factor in enterohemorrhagic E. coli (EHEC). Using transcriptomics, mutagenesis, and ligand-binding assays, we demonstrate that EHEC’s type III secretion system is repressed when the bacteria’s folate biosynthetic pathway is pharmacologically disrupted, and that this effect is mediated by two regulatory proteins: PurR and McbR. Additionally, we identify dihydrofolate as a ligand of the previously orphaned McbR transcription regulator.

ORGANISM(S): Escherichia coli O157:H7

PROVIDER: GSE322789 | GEO | 2026/05/26

REPOSITORIES: GEO

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Project description:Enterohemorrhagic Escherichia coli (EHEC), including serotype O157:H7, cause severe food-borne illness. On route to the human colon, they encounter and resist, numerous anti-microbial ingestion stresses. We hypothesize that these stresses cue EHEC to alter virulence properties. This study investigated the impact of bile salts on virulence properties and examined the genetic basis of the phenotypes. Established assays were used to examine adhesion to human epithelial cells, motility, verotoxin (VT) production and antimicrobial resistance with/without bile salt stress. Bacteria treated for 90 minute in DMEM plus 0.15% (w/v) bile salt mix demonstrated significantly enhanced adhesion to epithelial cells and resistance to several antibiotics but did not increase motility or VT production. To determine the genetic basis of these phenotypes a microarray experiment was conducted. EHEC strain 86-24, in mid-log phase of growth, were grown in DMEM pH 7.4 (control), or DMEM plus bile salt mix (0.15% w/v), for 90 minutes, statically at 37˚C, 5% CO2 prior to harvesting RNA for the microarray study. Four biological replicates were produced for each treatment. Microarray and gene expression analysis (semi-quantitative RT-PCR and beta-galactosidase reporter assays) of bile salt-treated EHEC revealed significant up-regulation of genes for lipid A modification, fimbriae, an efflux pump, and a two-component regulatory system relative to the bacteria grown in DMEM alone. This work points to several mechanisms that EHEC employs to resist the stresses of the human small intestine, notably efflux, antimicrobial resistance, and outer membrane alterations. Bile salts enhanced the virulence-related properties of increased adhesion and resistance to antimicrobials but not VT production or motility. This research contributes to our understanding of how EHEC senses and responds to host environmental signals and the mechanisms this pathogen uses to successfully colonize and infect the human host.

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The McbR transcription factor links intracellular folate pool to virulence in enteric pathogens

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