The sRNA DicF integrates oxygen sensing to enhance enterohemorrhagicEscherichia colivirulence via distinctive RNA control mechanisms

Abstract

To establish infection, enteric pathogens integrate environmental cues to navigate the gastrointestinal tract (GIT) and precisely control expression of virulence determinants. During passage through the GIT, pathogens encounter relatively high levels of oxygen in the small intestine before transit to the oxygen-limited environment of the colon. However, how bacterial pathogens sense oxygen availability and coordinate expression of virulence traits is not resolved. Here, we demonstrate that enterohemorrhagicEscherichia coliO157:H7 (EHEC) regulates virulence via the oxygen-responsive small RNA DicF. Under oxygen-limited conditions, DicF enhances global expression of the EHEC type three secretion system, which is a key virulence factor required for host colonization, through the transcriptional activator PchA. Mechanistically, thepchAcoding sequence (CDS) base pairs with the 5′ untranslated region of the mRNA to sequester the ribosome binding site (RBS) and inhibit translation. DicF disruptspchA cis-interactions by binding to thepchACDS, thereby unmasking thepchARBS and promoting PchA expression. These findings uncover a feed-forward regulatory pathway that involves distinctive mechanisms of RNA-based regulation and that provides spatiotemporal control of EHEC virulence.