Hfq reduces envelope stress by controlling expression of envelope‐localized proteins and protein complexes in enteropathogenic E scherichia coli

Summary G ram‐negative bacteria possess several envelope stress responses that detect and respond to damage to this critical cellular compartment. The σ E envelope stress response senses the misfolding of outer membrane proteins ( OMPs ), while the Cpx two‐component system is believed to detect the misfolding of periplasmic and inner membrane proteins. Recent studies in several G ram‐negative organisms found that deletion of hfq , encoding a small RNA chaperone protein, activates the σ E envelope stress response. In this study, we assessed the effects of deleting hfq upon activity of the σ E and Cpx responses in non‐pathogenic and enteropathogenic ( EPEC ) strains of E scherichia coli . We found that the σ E response was activated in Δ hfq mutants of all E . coli strains tested, resulting from the misregulation of OMPs . The Cpx response was activated by loss of hfq in EPEC , but not in E . coli   K ‐12. Cpx pathway activation resulted in part from overexpression of the bundle‐forming pilus ( BFP ) in EPEC Δ hfq . We found that Hfq repressed expression of the BFP via PerA , a master regulator of virulence in EPEC . This study shows that Hfq has a more extensive role in regulating the expression of envelope proteins and horizontally acquired virulence genes in E . coli than previously recognized.