sRNAs in EHEC virulence

PROJECT SUMMARY The ability of bacteria to rapidly sense and respond to changes in the environment is fundamental to colonization and survival. This is especially relevant for gastrointestinal pathogens that must effectively compete for nutrients with the microbiota as well as precisely coordinate gene expression to establish infection. Small RNAs (sRNAs) are emerging as important factors that enable efficient spatiotemporal expression of genes in response to the availability of a specific metabolite and/or environmental cues, and thus play a central role in pathogenesis. The bacterial pathogen enterohemorrhagic Escherichia coli O157:H7 (EHEC) colonizes the human colon and causes hemorrhagic colitis and hemolytic uremic syndrome (HUS), which can be fatal. EHEC encodes several important virulence factors, including the potent Shiga toxin that causes HUS and a type three secretion system (T3SS) and effectors necessary for attaching and effacing (AE) lesion formation on enterocytes. EHEC has a very low infectious dose, suggesting that EHEC has evolved mechanisms to exploit nutrients in the host and precisely control virulence gene expression to occur within appropriate host niches. Our studies underscore the importance of sRNAs in bacterial virulence by demonstrating that two sRNAs, DicF and MavR, play important roles in modulating EHEC virulence. DicF influences expression of the T3SS and is required for AE lesion formation. DicF also modulates expression of genes encoding Shiga toxin, transcriptional regulators, and adhesins. MavR regulates EHEC metabolism as well as stress responses and is essential for robust colonization of the mammalian gastrointestinal tract. Moreover, our data indicate that these sRNAs regulate target gene expression via unusual mechanisms. In this application, we will investigate the molecular mechanisms of DicF- and MavR-dependent gene regulation and comprehensively identify direct targets of DicF and MavR. The proposed studies will shed light not only on EHEC virulence but also on sRNA- dependent regulatory mechanisms that may be important for gene regulation in diverse bacterial pathogens.