The Characterization of the Fucose Sensing Kinase (FUSK) and the Fucose Sensing Response Regulator (FUSR) and Their Role in Virulence Regulation in Enterohemorrhagic Escherichia Coli O157:H7




Pacheco, Alline Roberta

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EHEC causes outbreaks of bloody diarrhea worldwide, by colonizing the human large intestine, where it forms attaching and effacing (AE) lesions on the intestinal epithelium. AE lesion development requires the presence of the locus of enterocyte effacement (LEE) that encodes for a molecular syringe, a type three secretion system (T3SS), which translocates effectors to the host cell. Expression of the LEE is controlled by the AI-3/Epi/NE interkingdom signaling cascade. The two-component systems QseBC and QseEF are at the core of the AI-3/Epi/NE signaling, controlling expression of flagellar motility genes, the LEE and type 3 secreted effectors in response to AI-3 and the catecholamine hormones Epi and NE. The network of regulatory proteins that form the AI-3/Epi/NE continues to expand, as shown by recent studies from our laboratory. Microarray analyses indicate that a putative two-component system (TCS), herein named FusKR, is repressed by QseBC and QseEF. FusK is the histidine kinase and FusR is the response regulator. In this work, we started to unravel the role of FusKR in EHEC pathogenicity. We constructed isogenic knockouts of fusK and fusR, and investigated their participation in virulence gene regulation in EHEC. Microarray analysis shows that deletion of fusK and fusR alters transcription of virulence and metabolic genes. Phenotypic analyses show that fusK- and fusR- strains are hypervirulent in vitro, overexpress the LEE genes and produces higher amounts of the T3 secreted protein EspB. Nonetheless, the fusK mutant is attenuated for colonization of the mammalian intestine. Biochemical studies revealed that FusK senses fucose. Fucose is an important carbon source for commensal and pathogenic bacteria during intestinal colonization. Transcriptional analyses shows that FusKR signal transduction system regulates fucose utilization indirectly, through regulation of the predicted membrane transporter Z0461, involved in optimal fucose uptake. Gut commensal Bacteroides thetaiomicron (B.theta) degrades mucin, releasing free monosaccharides, including fucose, into the gut lumen. Co-culture of B.theta and EHEC on mucin indicates that this commensal supplies mucin-derived fucose to EHEC, reducing expression of the LEE. Our studies demonstrate that a novel TCS, FusKR, modulates intestinal colonization by EHEC, and it is involved in complex interactions with the microbiota during infection.

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