Article

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: 3.83). 12/2007; 189(21):7752-64. DOI:10.1128/JB.01797-06
Source: PubMed

ABSTRACT 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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Keywords

AlgR
 
AlgR controls numerous virulence factors
 
algR deletion strain
 
algR mutant
 
biofilm growth
 
biofilm-grown PAO1
 
biofilm-specific manner
 
chromosomal mutated AlgR binding site
 
DeltaalgR
 
N-butyryl homoserine lactone
 
normal biofilm development
 
quorum-sensing genes
 
Rhl quorum-sensing system
 
rhlI promoter
 
rhlI promoters
 
static biofilm assays
 
Strain PSL317
 
type IV pilus-mediated twitching motility
 
wild-type biofilm phenotype
 
wild-type strain PAO1