Post-transcriptional regulation of virulence gene expression in enterohemorrhagic E. coli O157:H7

Pathogenic bacteria must be able to withstand harsh conditions in environmental reservoirs until the opportune time of infecting a host. Foodborne pathogens survive within distinct niches in the environment and adapt methods to persist during food processing and preparation until ultimately infecting a human host. Once inside the gastrointestinal (GI) tract, foodborne pathogens combat host defense mechanisms to finally colonize the small or large intestines. Virulence genes required for colonization must be precisely controlled to ensure expression at the appropriate location. To accomplish these feats, pathogens integrate signals from the environment into outputs that modulate gene expression to adapt to changing conditions. These outputs affect transcription, as well as post-transcriptional and post-translational regulation. Post-transcriptional regulation, in particular, allows for rapid adaptation to changing environments. Post-transcriptional regulation occurs through the activity of small non-coding RNAs (sRNAs) and/or RNA-binding proteins.
The foodborne pathogen enterohemorrhagic Escherichia coli O157:H7 (EHEC) causes GI illness associated with consuming undercooked meats and contaminated produce. EHEC encodes the locus of enterocyte effacement (LEE), a pathogenicity island critical for tight adherence of EHEC to the epithelial barrier of the colon. The infectious dose of EHEC is unusually low, requiring as few as 50 bacteria to cause disease, suggesting that EHEC evolved mechanisms to tightly control virulence gene expression. LEE expression in EHEC responds to different signals that lead to transcriptional and post-transcriptional outputs to control this critical virulence factor and promote expression when appropriate.
In this dissertation, we characterize two pathways that promote LEE expression post-transcriptionally in EHEC. We identify a new mechanism of sRNA activation of gene expression, describing an sRNA that promotes LEE expression in response to low oxygen conditions, which mimic the environment EHEC encounters when establishing infection in the colon. In addition, we characterize an RNA helicase that promotes LEE expression by repressing the expression of a negative LEE-regulator. In total, we describe complex regulatory pathways that control virulence gene expression, providing new insights into post-transcriptional gene regulation in bacteria.