CpxR/OmpR Interplay Regulates Curli Gene Expression in Response to Osmolarity inEscherichia coli

Abstract

Curli fibers could be described as a virulence factor able to confer adherence properties to both abiotic and eukaryotic surfaces. The ability to adapt rapidly to changing environmental conditions through signal transduction pathways is crucial for the growth and pathogenicity of bacteria. OmpR was shown to activate csgD expression, resulting in curli production. The CpxR regulator was shown to negatively affect curli gene expression when binding to its recognition site that overlaps the csgD OmpR-binding site. This study was undertaken to clarify how the interplay between the two regulatory proteins, OmpR and CpxR, can affect the transcription of the curli gene in response to variation of the medium osmolarity. Band-shift assays with purified CpxR proteins indicate that CpxR binds to the csgD promoter region at multiple sites that are ideally positioned to explain the csg repression activity of CpxR. To understand the physiological meaning of this in vitro molecular phenomenon, we analyzed the effects of an osmolarity shift on the two-component pathway CpxA/CpxR. We establish here that the Cpx pathway is activated at both transcriptional and posttranscriptional levels in response to a high osmolarity medium and that CpxR represses csgD expression in high-saltcontent medium, resulting in low curli production. However, csgD repression in response to high sucrose content is not mediated by CpxR but by the global regulatory protein H-NS. Therefore, multiple systems (EnvZ/OmpR, Cpx, Rcs, and H-NS) appear to be involved in sensing environmental osmolarity, leading to sophisticated regulation of the curli genes.

Uropathogenic Escherichia coli CFT073 Is Adapted to Acetatogenic Growth but Does Not Require Acetate during Murine Urinary Tract Infection

“…A probable role for acetyl phosphate metabolism in extraintestinal, gram-negative pathogenesis is in the indirect effect acetyl phosphate has on the histone-like protein H-NS (21). H-NS is capable of repressing numerous processes, often associated with horizontally acquired DNA that plays a role in pathogenesis (5,14,16,17,23,27,34). UPEC 536 hns upregulated numerous virulence factors (34) similarly to a CFT073 mutant that colonizes the murine urinary tract in a robust fashion (19).…”

Comparative Genetics of the rdar Morphotype inSalmonella

“…Phosphorylated CpxR (CpxR-P) acts as a repressor of agfD transcription in high salt concentrations, through binding to sites in both agfD and agfB promoter regions (35,46). Additional regulatory proteins affecting agfD transcription include HN-S and integration host factor (IHF) (24,35), as well as the RcsC/B (19) and TolQRA (63) systems.…”

GlcNAc-6P Levels Modulate the Expression of Curli Fibers byEscherichia coli

“…Three two-component regulatory systems, Rcs, CpxA/R, and OmpR/EnvZ, regulate curli gene expression. The Rcs pathway positively regulates capsule synthesis in response to changes in the cell surface and negatively regulates both curli operons (19,26,31,52). The CpxA/R system, which responds to envelope stress, negatively regulates both curli operons (16,18).…”