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Infection and Immunity, September 2009, p. 3552-3568, Vol. 77, No. 9
0019-9567/09/$08.00+0     doi:10.1128/IAI.00418-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

The RNA Binding Protein CsrA Is a Pleiotropic Regulator of the Locus of Enterocyte Effacement Pathogenicity Island of Enteropathogenic Escherichia coli{triangledown}

Shantanu Bhatt,1,2 Adrianne Nehrling Edwards,2 Hang Thi Thu Nguyen,3 Didier Merlin,3 Tony Romeo,2,4 and Daniel Kalman1,2*

Department of Pathology and Laboratory Medicine, Emory University, Atlanta, Georgia 30322,1 Microbiology and Molecular Genetics Program, Emory University, Atlanta, Georgia 30322,2 Department of Medicine, Division of Digestive Diseases, Emory University School of Medicine, Atlanta, Georgia 30322,3 Department of Microbiology and Cell Science, P.O. Box 110700, University of Florida, Gainesville, Florida 32611-07004

Received 15 April 2009/ Returned for modification 22 May 2009/ Accepted 26 June 2009

The attaching and effacing (A/E) pathogen enteropathogenic Escherichia coli (EPEC) forms characteristic actin-filled membranous protrusions upon infection of host cells termed pedestals. Here we examine the role of the RNA binding protein CsrA in the expression of virulence genes and proteins that are necessary for pedestal formation. The csrA mutant was defective in forming actin pedestals on epithelial cells and in disrupting transepithelial resistance across polarized epithelial cells. Consistent with reduced pedestal formation, secretion of the translocators EspA, EspB, and EspD and the effector Tir was substantially reduced in the csrA mutant. Purified CsrA specifically bound to the sepL espADB mRNA leader, and the corresponding transcript levels were reduced in the csrA mutant. In contrast, Tir synthesis was unaffected in the csrA mutant. Reduced secretion of Tir appeared to be in part due to decreased synthesis of EscD, an inner membrane architectural protein of the type III secretion system (TTSS) and EscF, a protein that forms the protruding needle complex of the TTSS. These effects were not mediated through the locus of enterocyte effacement (LEE) transcriptional regulator GrlA or Ler. In contrast to the csrA mutant, multicopy expression of csrA repressed transcription from LEE1, grlRA, LEE2, LEE5, escD, and LEE4, an effect mediated by GrlA and Ler. Consistent with its role in other organisms, CsrA also regulated flagellar motility and glycogen levels. Our findings suggest that CsrA governs virulence factor expression in an A/E pathogen by regulating mRNAs encoding translocators, effectors, or transcription factors.

* Corresponding author. Mailing address: Department of Pathology, 615 Michael St., Atlanta, GA 30322. Phone: (404) 712-2326. Fax: (404) 712-2979. E-mail: dkalman{at}emory.edu

{triangledown} Published ahead of print on 6 July 2009.

Editor: A. J. Bäumler

Infection and Immunity, September 2009, p. 3552-3568, Vol. 77, No. 9
0019-9567/09/$08.00+0     doi:10.1128/IAI.00418-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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