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Transcriptional regulators of the GAD acid stress island are carried by effector protein-encoding prophages and indirectly control type III secretion in enterohemorrhagic Escherichia coli O157:H7.

ABSTRACT: Type III secretion (T3S) plays a pivotal role in the colonization of ruminant hosts by Enterohemorrhagic Escherichia coli (EHEC). The T3S system translocates effector proteins into host cells to promote bacterial attachment and persistence. The repertoire and variation in prophage regions underpins differences in the pathogenesis and epidemiology of EHEC strains. In this study, we have used a collection of deletions in cryptic prophages and EHEC O157 O-islands to screen for novel regulators of T3S. Using this approach we have identified a family of homologous AraC-like regulators that indirectly repress T3S. These prophage-encoded secretion regulator genes (psr) are found exclusively on prophages and are associated with effector loci and the T3S activating Pch family of regulators. Transcriptional profiling, mutagenesis and DNA binding studies were used to show that these regulators usurp the conserved GAD acid stress resistance system to regulate T3S by increasing the expression of GadE (YhiE) and YhiF and that this regulation follows attachment to bovine epithelial cells. We further demonstrate that PsrA and effectors encoded within cryptic prophage CP933-N are required for persistence in a ruminant model of colonization.

SUBMITTER: Tree JJ

PROVIDER: S-EPMC7099609 | biostudies-literature | 2011 Jun

REPOSITORIES: biostudies-literature

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Transcriptional regulators of the GAD acid stress island are carried by effector protein-encoding prophages and indirectly control type III secretion in enterohemorrhagic Escherichia coli O157:H7.

Tree Jai J JJ Roe Andrew J AJ Flockhart Allen A McAteer Sean P SP Xu Xuefang X Shaw Darren D Mahajan Arvind A Beatson Scott A SA Best Angus A Lotz Sabrina S Woodward Martin J MJ La Ragione Roberto R Murphy Kenan C KC Leong John M JM Gally David L DL

Molecular microbiology 20110415 5

Type III secretion (T3S) plays a pivotal role in the colonization of ruminant hosts by Enterohemorrhagic Escherichia coli (EHEC). The T3S system translocates effector proteins into host cells to promote bacterial attachment and persistence. The repertoire and variation in prophage regions underpins differences in the pathogenesis and epidemiology of EHEC strains. In this study, we have used a collection of deletions in cryptic prophages and EHEC O157 O-islands to screen for novel regulators of T ...[more]

PMID: 21492263

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Project description:Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a foodborne pathogen producing Shiga toxins (Stx1 and Stx2), which can cause hemorrhagic diarrhea and life-threatening infections. O157:H7 strain EDL933 carries prophages CP-933V and BP-933W, which encode Shiga toxin genes (stx1 and stx2, respectively). The aim of this work was to investigate the mechanisms of adaptive resistance of EHEC strain EDL933 to a typically lethal dose of gamma irradiation (1.5 kGy). Adaptive selection through six passages of exposure to 1.5 kGy resulted in the loss of CP-933V and BP-933W prophages from the genome and mutations within three genes: wrbA, rpoA, and Wt_02639 (molY). Three selected EHEC clones that became irradiation adapted to the 1.5-kGy dose (C1, C2, and C3) demonstrated increased resistance to oxidative stress, sensitivity to acid pH, and decreased cytotoxicity to Vero cells. To confirm that loss of prophages plays a role in increased radioresistance, clones C1 and C2 were exposed to bacteriophage-containing lysates. Although phage BP-933W could lysogenize C1, C2, and E. coli K-12 strain MG1655, it was not found to have integrated into the bacterial chromosome in C1-Φ and C2-Φ lysogens. Interestingly, for the E. coli K-12 lysogen (K-12-Φ), BP-933W DNA had integrated at the wrbA gene (K-12-Φ). Both C1-Φ and C2-Φ lysogens regained sensitivity to oxidative stress, were more effectively killed by a 1.5-kGy gamma irradiation dose, and had regained cytotoxicity and acid resistance phenotypes. Further, the K-12-Φ lysogen became cytotoxic, more sensitive to gamma irradiation and oxidative stress, and slightly more acid resistant. IMPORTANCE Gamma irradiation of food products can provide an effective means of eliminating bacterial pathogens such as enterohemorrhagic Escherichia coli (EHEC) O157:H7, a significant foodborne pathogen that can cause severe disease due to the production of Stx. To decipher the mechanisms of adaptive resistance of the O157:H7 strain EDL933, we evolved clones of this bacterium resistant to a lethal dose of gamma irradiation by repeatedly exposing bacterial cells to irradiation following a growth restoration over six successive passages. Our findings provide evidence that adaptive selection involved modifications in the bacterial genome, including deletion of the CP-933V and BP-933W prophages. These mutations in EHEC O157:H7 resulted in loss of stx1 and stx2, loss of cytotoxicity to epithelial cells, and decreased resistance to acidity, critical virulence determinants of EHEC, concomitant with increased resistance to lethal irradiation and oxidative stress. These findings demonstrate that the potential adaptation of EHEC to high doses of radiation would involve elimination of the Stx-encoding phages and likely lead to a substantial attenuation of virulence.

Project description:The large intestinal pathogen enterohemorrhagic Escherichia coli (EHEC) O157:H7 detects host cues to regulate virulence gene expression during colonization and infection. However, virulence regulatory mechanisms of EHEC O157:H7 in the human large intestine are not fully understood. Herein, we identified a virulence-regulating pathway where the PhoQ/PhoP two-component regulatory system senses low magnesium levels and signals to the O island 119-encoded Z4267 (LmiA; low magnesium-induced regulator A), directly activating loci of enterocyte effacement genes to promote EHEC O157:H7 adherence in the large intestine. Disruption of this pathway significantly decreased EHEC O157:H7 adherence in the mouse intestinal tract. Moreover, feeding mice a magnesium-rich diet significantly reduced EHEC O157:H7 adherence in vivo This LmiA-mediated virulence regulatory pathway is also conserved among several EHEC and enteropathogenic E. coli serotypes; therefore, our findings support the use of magnesium as a dietary supplement and provide greater insights into the dietary cues that can prevent enteric infections.IMPORTANCE Sensing specific gut metabolites is an important strategy for inducing crucial virulence programs by enterohemorrhagic Escherichia coli (EHEC) O157:H7 during colonization and infection. Here, we identified a virulence-regulating pathway wherein the PhoQ/PhoP two-component regulatory system signals to the O island 119-encoded low magnesium-induced regulator A (LmiA), which, in turn, activates locus of enterocyte effacement (LEE) genes to promote EHEC O157:H7 adherence in the low-magnesium conditions of the large intestine. This regulatory pathway is widely present in a range of EHEC and enteropathogenic E. coli (EPEC) serotypes. Disruption of this pathway significantly decreased EHEC O157:H7 adherence in the mouse intestinal tract. Moreover, mice fed a magnesium-rich diet showed significantly reduced EHEC O157:H7 adherence in vivo, indicating that magnesium may help in preventing EHEC and EPEC infection in humans.

Dataset Information

Transcriptional regulators of the GAD acid stress island are carried by effector protein-encoding prophages and indirectly control type III secretion in enterohemorrhagic Escherichia coli O157:H7.

Publications

Transcriptional regulators of the GAD acid stress island are carried by effector protein-encoding prophages and indirectly control type III secretion in enterohemorrhagic Escherichia coli O157:H7.

Similar Datasets

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