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Journal of Bacteriology, June 2005, p. 4086-4094, Vol. 187, No. 12
0021-9193/05/$08.00+0     doi:10.1128/JB.187.12.4086-4094.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

ClpXP Protease Controls Expression of the Type III Protein Secretion System through Regulation of RpoS and GrlR Levels in Enterohemorrhagic Escherichia coli

Sunao Iyoda* and Haruo Watanabe

Department of Bacteriology, National Institute of Infectious Diseases, Toyama 1-23-1, Shinjuku-ku, Tokyo 162-8640, Japan

Received 24 January 2005/ Accepted 18 March 2005

Expression of the type III protein secretion system (TTSS), encoded in the locus of enterocyte effacement (LEE) of enterohemorrhagic Escherichia coli (EHEC), has been shown to be controlled by various regulators. In a search for additional regulatory genes, we identified a DNA fragment containing clpX and clpP that has a positive regulatory effect on LEE expression in EHEC O157. The expression of LEE-encoded Esp proteins was significantly reduced in a clpXP deletion mutant. Deletion of grlR, a negative regulatory gene within LEE, markedly increased LEE expression even in the clpXP mutant. To verify the regulatory mechanism of GrlR expression, a chromosomal epitope-tagged allele of grlR (grlR-FLAG) was constructed. GrlR-FLAG expression was increased significantly in the clpXP deletion mutant, suggesting that the GrlR level is under the control of ClpXP, and this regulation is critical for the ClpXP-dependent expression of LEE in EHEC. Deletion of rpoS, the gene encoding a stationary-phase-inducing sigma factor that is a substrate for ClpXP protease, partially restored LEE expression in the clpXP mutant. A multicopy plasmid carrying rpoS strongly repressed expression of Esp proteins, suggesting that positive regulation by ClpXP is partially mediated through a negative effect of RpoS on LEE expression. We also found that rpoS deletion induces transcription of pchA, which encodes one of the positive regulators for LEE expression in EHEC. These results suggest that ClpXP controls expression of LEE through the regulation of RpoS and GrlR levels in EHEC.

* Corresponding author. Mailing address: Department of Bacteriology, National Institute of Infectious Diseases, Toyama 1-23-1, Shinjuku-ku, Tokyo 162-8640, Japan. Phone: 81-3-5285-1111. Fax: 81-3-5285-1163. E-mail: siyoda{at}nih.go.jp.

Journal of Bacteriology, June 2005, p. 4086-4094, Vol. 187, No. 12
0021-9193/05/$08.00+0     doi:10.1128/JB.187.12.4086-4094.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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