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Journal of Bacteriology, November 2007, p. 7752-7764, Vol. 189, No. 21
0021-9193/07/$08.00+0     doi:10.1128/JB.01797-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Pseudomonas aeruginosa AlgR Represses the Rhl Quorum-Sensing System in a Biofilm-Specific Manner ^,

Department of Microbiology and Immunology, Program in Molecular Pathogenesis and Immunity, Tulane University Health Sciences Center, New Orleans, Louisiana 70112,¹ Department of Microbiology and Immunology, University of Rochester, Rochester, New York 14642,² Department of Genetics, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112,³ University of Cincinnati College of Medicine, Department of Molecular Genetics, Biochemistry, and Microbiology, Cincinnati, Ohio 45267,⁴ Department of Biological Sciences, State University of New York at Binghamton, Binghamton, New York 13902,⁵ University of Colorado at Denver and Health Sciences Center, Department of Microbiology, Aurora, Colorado 80045⁶

Received 28 November 2006/ Accepted 22 August 2007

AlgR controls numerous virulence factors in Pseudomonas aeruginosa, including alginate, hydrogen cyanide production, and type IV pilus-mediated twitching motility. In this study, the role of AlgR in biofilms was examined in continuous-flow and static biofilm assays. Strain PSL317 (algR) produced one-third the biofilm biomass of wild-type strain PAO1. Complementation with algR, but not fimTU-pilVWXY1Y2E, restored PSL317 to the wild-type biofilm phenotype. Comparisons of the transcriptional profiles of biofilm-grown PAO1 and PSL317 revealed that a number of quorum-sensing genes were upregulated in the algR deletion strain. Measurement of rhlA::lacZ and rhlI::lacZ promoter fusions confirmed the transcriptional profiling data when PSL317 was grown as a biofilm, but not planktonically. Increased amounts of rhamnolipids and N-butyryl homoserine lactone were detected in the biofilm effluent but not the planktonic supernatants of the algR mutant. Additionally, AlgR specifically bound to the rhlA and rhlI promoters in mobility shift assays. Moreover, PAO1 containing a chromosomal mutated AlgR binding site in its rhlI promoter formed biofilms and produced increased amounts of rhamnolipids similarly to the algR deletion strain. These observations indicate that AlgR specifically represses the Rhl quorum-sensing system during biofilm growth and that such repression is necessary for normal biofilm development. These data also suggest that AlgR may control transcription in a contact-dependent or biofilm-specific manner.

Published ahead of print on 31 August 2007.

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