Characterization of the Citrobacter rodentium Cpx regulon and its role in host infection

Abstract

Summary Envelope‐localized proteins, such as adhesins and secretion systems, play critical roles in host infection by Gram‐negative pathogens. As such, their folding is monitored by envelope stress response systems. Previous studies demonstrated that the Cpx envelope stress response is required for virulence of Citrobacter rodentium, a murine pathogen used to model infections by the human pathogens enteropathogenic and enterohemorrhagic Escherichia coli; however, the mechanisms by which the Cpx response promotes host infection were previously unknown. Here, we characterized the C. rodentium Cpx regulon in order to identify genes required for host infection. Using transcriptomic and proteomic approaches, we found that the Cpx response upregulates envelope‐localized protein folding and degrading factors but downregulates pilus genes and type III secretion effectors. Mouse infections with C. rodentium strains lacking individual Cpx‐regulated genes showed that the chaperone/protease DegP and the disulfide bond oxidoreductase DsbA were essential for infection, but Cpx regulation of these genes did not fully account for attenuation of C. rodentium ΔcpxRA. Both deletion of dsbA and treatment with the reducing agent dithiothreitol activated the C. rodentium Cpx response, suggesting that it may sense disruption of disulfide bonding. Our results highlight the importance of envelope protein folding in host infection by Gram‐negative pathogens.

Maintaining Integrity Under Stress: Envelope Stress Response Regulation of Pathogenesis in Gram-Negative Bacteria

“…Deleting cpxRA attenuates the ability of C. rodentium to colonize and cause death in mice, in some cases completely (Thomassin et al, 2015, 2017; Vogt et al, 2019). cpx gene expression is induced during infection suggesting that the response is activated during host colonization (Thomassin et al, 2015, 2017).…”

“…Deleting cpxP or nlpE had no significant impact on colonization, virulence or ability to bind to HeLa cells unlike the cpxRA null mutant which was attenuated in all these aspects (Giannakopoulou et al, 2018). Attenuation of virulence was found to be independent of type III secretion and growth rate, as secretion profiles and growth rates remain relatively the same as compared to wildtype in cpxRA mutants (Thomassin et al, 2015; Vogt et al, 2019).…”

“…Interestingly, it was recently reported that deleting the Cpx-regulated genes degP/htrA and dsbA led to a reduction in secreted protein levels of the T3SS translocator protein EspB in C. rodentium (Vogt et al, 2019). Furthermore, deleting degP or dsbA caused C. rodentium to become completely avirulent, unlike cpxRA , which in this study resulted in less attenuation of virulence compared to previous studies (Thomassin et al, 2015, 2017; Vogt et al, 2019). The reason for the difference between these studies is currently unknown.…”

Here, there, and everywhere: How pathogenicEscherichia colisense and respond to gastrointestinal biogeography

“…CpxRA was found to regulate expression of hundreds of genes and proteins at the transcriptional and post‐transcriptional/post‐translational level, including downregulation of the Kfc pilus, several T3S effectors, and Pdu propanediol utilisation microcompartment proteins, the expression of which are energetically expensive and could impair in vivo growth. CpxRA‐regulated genes encoding DegP, a periplasmic protease, and DsbA, a disulfide bond oxidoreductase, were found to be essential for virulence in mice (Vogt et al, ). As mammalian cells do not have TCSs, they present key targets for antimicrobial drugs (Bem et al, ).…”

“…CpxRA plays an important role in the envelope stress response of E. coli, by monitoring membrane protein folding, as reviewed by Guest and Raivio (2016). CpxRA was found to regulate CpxRA-regulated genes encoding DegP, a periplasmic protease, and DsbA, a disulfide bond oxidoreductase, were found to be essential for virulence in mice (Vogt et al, 2018). As mammalian cells do not have TCSs, they present key targets for antimicrobial drugs (Bem et al, 2015).…”