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Journal of Bacteriology, March 2001, p. 1531-1539, Vol. 183, No. 5
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.5.1531-1539.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Inhibition of Quorum Sensing by a Pseudomonas aeruginosa dksA Homologue

Pavel Branny,1 James P. Pearson,2 Everett C. Pesci,3 Thilo Köhler,1 Barbara H. Iglewski,4 and Christian Van Delden1,*

Department of Genetics and Microbiology, Centre Médical Universitaire, CH 1211 Geneva 4, Switzerland1; Department of Microbiology, Protein Design Labs, Fremont, California 945552; Department of Microbiology and Immunology, East Carolina University, Greenville, North Carolina 278583; and Department of Microbiology and Immunology, University of Rochester, Rochester, New York 146424

Received 23 August 2000/Accepted 27 November 2000

The Pseudomonas aeruginosa las (lasR-lasI) and rhl (rhlR-rhlI) quorum-sensing systems regulate the expression of several virulence factors, including elastase and rhamnolipid. P. aeruginosa strain PR1-E4 is a lasR deletion mutant that contains a second, undefined mutation which allows production of elastase and rhamnolipid despite a nonfunctional las system. We have previously shown that this strain accomplishes this by increasing the expression of the autoinducer synthase gene rhlI. In this report, we show that the elastolytic phenotype of mutant PR1-E4 can be complemented with a P. aeruginosa homologue of the Escherichia coli dnaK mutation suppressor gene dksA. When supplied in trans on a multicopy plasmid, this gene completely suppressed elastase production by mutant PR1-E4. Cloning and Northern blot analysis revealed that dksA was neither mutated nor less transcribed in mutant PR1-E4. When overexpressed, dksA also reduced rhamnolipid production by both mutant PR1-E4 and the wild type, PAO1. Using Northern blot analysis and lacZ reporter fusions, we show that dksA inhibits rhlI, rhlAB, and lasB transcription. Exogenous N-butyryl-L-homoserine lactone overcame the reduced expression of rhlI and restored rhlAB and lasB expression, as well as elastase production. Our results suggest that the overproduction of the P. aeruginosa DksA homologue inhibits quorum-sensing-dependent virulence factor production by downregulating the transcription of the autoinducer synthase gene rhlI.

* Corresponding author: Mailing address: Department of Genetics and Microbiology, Medical School of the University of Geneva, CMU, 9 av. Champel, CH-1211 Geneva 4, Switzerland. Phone: (4122) 702 56 55. Fax: (4122) 702 57 02. E-mail: Christian.vanDelden{at}medecine.unige.ch.

Journal of Bacteriology, March 2001, p. 1531-1539, Vol. 183, No. 5
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.5.1531-1539.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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