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Journal of Bacteriology, March 2005, p. 2038-2049, Vol. 187, No. 6
0021-9193/05/$08.00+0     doi:10.1128/JB.187.6.2038-2049.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

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

Gregory Jubelin,1 Anne Vianney,2 Christophe Beloin,3 Jean-Marc Ghigo,3 Jean-Claude Lazzaroni,2 Philippe Lejeune,1 and Corinne Dorel1*

Unité de Microbiologie et Génétique Composante INSA,1 Unité de Microbiologie et Génétique, Université Claude Bernard Lyon I, Villeurbanne,2 Groupe de Génétique des Biofilms, Institut Pasteur, Paris, France3

Received 2 August 2004/ Accepted 6 December 2004

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-salt-content 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.

* Corresponding author. Mailing address: Unité de Microbiologie et Génétique Composante INSA, 10 rue Dubois, 69 622 Villeurbanne Cedex, France. Phone: 33(0)4-72-43-19-86. Fax: 33(0)4-72-43-15-84. E-mail: corinne.dorel{at}insa-lyon.fr.

Journal of Bacteriology, March 2005, p. 2038-2049, Vol. 187, No. 6
0021-9193/05/$08.00+0     doi:10.1128/JB.187.6.2038-2049.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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