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, LA, 70112, Department of Microbiology and Immunology, University of Rochester, Rochester, NY, 14642, Department of Genetics, Louisiana State University Health Sciences Center, New Orleans, LA, 70112, University of Cincinnati College of Medicine, Department of Molecular Genetics, Biochemistry and Microbiology, Cincinnati, OH 45267, Department of Biological Sciences, State University of New York at Binghamton, Binghamton, NY,13902, University of Colorado at Denver Health Science Center, Department of Microbiology, Aurora, CO 80045

^* To whom correspondence should be addressed. Email: Michael.schurr{at}uchsc.edu.

	Abstract

AlgR controls numerous virulence factors in Pseudomonas aeruginosa, including alginate, hydrogen cyanide (HCN) production, and type-IV pili 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 fimTUpilVWXY1Y2E, 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 C₄-HSL were detected in the biofilm effluent but not 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 similar 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 through a contact-dependent or biofilm-specific manner.