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

SummaryType 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.

Global Regulator of Virulence A (GrvA) Coordinates Expression of Discrete Pathogenic Mechanisms in Enterohemorrhagic Escherichia coli through Interactions with GadW-GadE

“…RNA-seq analysis revealed that deletion of grvA leads to the upregulation of gadE, a known transcriptional repressor of LEE-encoded regulator ler (52,53). As such, the contribution of gadE to GrvA-dependent control of the LEE and adherence to cultured intestinal epithelial cells was examined.…”

“…GadE is a negative regulator of LEE expression, acting directly on the LEE1 promoter to repress ler transcription (52,53). In the preceding experiments, the upregulation of ler by GrvA was determined to correspond with gadE repression.…”

“…GrvA was shown to activate LEE-encoded master regulator ler through downregulation of gadE, the product of which directly represses ler transcription in EHEC (52,53,76). Negative control of gadE by GrvA is predicted to occur indirectly through the P3 promoter, requiring an intact gadW (Fig.…”

“…GrvA regulates the expression of Ͼ700 genes in EHEC O157:H7 strain TW14359. The model is inferred from the results of experiments performed in this and previous studies (20,21,52,53,55). See the text for further details.…”

Control of Acid Resistance Pathways of Enterohemorrhagic Escherichia coli Strain EDL933 by PsrB, a Prophage-Encoded AraC-Like Regulator

“…Recently, we and others showed that the prototypical EHEC O157:H7 strain, EDL933, carries three prophage-encoded loci, patE, psrA, and psrB, which encode AraC-like transcriptional regulators that downregulate the expression of the LEE-en-coded type III secretion pathway (24,25). Our previous work also demonstrated that PatE is involved in transcriptional activation of AR pathways of strain EDL933 (24).…”