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

Tulane University Health Sciences Center, Department of Microbiology and Immunology, New Orleans, LA 70112, USA.
Journal of Bacteriology (Impact Factor: 2.81). 12/2007; 189(21):7752-64. DOI: 10.1128/JB.01797-06
Source: PubMed


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 (DeltaalgR) 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.

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    • "However, AlgU regulates genes in addition to the alginate biosynthetic genes, including other transcriptional regulators, such as algR and the heat shock sigma factor rpoH [24], [25]. Previous studies have shown an increase in type III secretion systems, a decrease in flagellum production and the decrease in C4-HSL-dependent quorum sensing in biofilms are associated with mucA mutation [26]–[28]. Recently it was shown that the mucA22 mutation also affects the osmotic stress sensitivity of P. aeruginosa but only in stationary phase, suggesting that mucA22, in addition to affecting alginate production during growth, affects cellular physiology in non-growing cells, a factor that could be significant during chronic infections [29], [30]. "
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    • "Furthermore, GacA has been shown to positively affect lasR, rhlR, and rhlI transcription (Pessi et al. 2001). The alginate biosynthesis regulatory protein AlgR has been reported to negatively regulate the rhl system and rhlAB expression (Morici et al. 2007). Furthermore, the lipase LipC, has been described to positively affect rhamnolipid production (Rosenau et al. 2010). "
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    • "Proteins identified by peptide de novo sequencing are numbered and listed in Table 3 Appl Microbiol Biotechnol aeruginosa especially in cystic fibrosis, and its production is regulated by the transcription regulator AlgR (Ramsey and Wozniak 2005). AlgR is known to suppress rhamnolipid production during biofilm development (Morici et al. 2007), which may suggest that the high production of rhamnolipid in our experiments is enhanced by the absence of alginate production. "
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