title: Quorum sensing modulates colony morphology through alkyl quinolones in Pseudomonas aeruginosa.
abstract: BACKGROUND
  Acyl-homoserine lactone (acyl-HSL) and alkyl quinolone (AQ) based quorum-sensing (QS) systems are important for Pseudomonas aeruginosa virulence and biofilm formation. The effect of QS on biofilm formation is influenced by various genetic and environmental factors. Here, we used a colony biofilm assay to study the effect of the central acyl-HSL QS regulator, LasR, on biofilm formation and structure in the representative clinical P. aeruginosa isolate ZK2870.
  
  
  RESULTS
  A lasR mutant exhibited wrinkled colony morphology at 37°C in contrast to the smooth colony morphology of the wild-type. Mutational analysis indicated that wrinkling of the lasR mutant is dependent on pel, encoding a biofilm matrix exopolysaccharide. Suppressor mutagenesis and complementation analysis implicated the AQ signaling pathway as the link between las QS and colony morphology. In this pathway, genes pqsA-D are involved in the synthesis of 4-hydroxyalkyl quinolines ("Series A congeners"), which are converted to 3,4-dihydroxyalkyl quinolines ("Series B congeners", including the well-characterized Pseudomonas Quinolone Signal, PQS) by the product of the LasR-dependent pqsH gene. Measurement of AQ in the wild-type, the lasR pqsA::Tn suppressor mutant as well as the defined lasR, pqsH, and lasR pqsH mutants showed a correlation between 4-hydroxyalkyl quinoline levels and the degree of colony wrinkling. Most importantly, the lasR pqsH double mutant displayed wrinkly morphology without producing any 3,4-dihydroxyalkyl quinolines. Constitutive expression of pqsA-D genes in a lasR pqsR::Tnmutant showed that colony wrinkling does not require the AQ receptor PqsR.
  
  
  CONCLUSIONS
  Taken together, these results indicate that the las QS system represses Pel and modulates colony morphology through a 4-hydroxyalkyl quinoline in a PqsR-independent manner, ascribing a novel function to an AQ other than PQS in P. aeruginosa.
authors.affiliation: Department of Microbiology, Oregon State University, Corvallis, 97331, USA.
authors.forename: Rashmi
authors.initials: R
authors.lastname: Gupta
authors.forename: Martin
authors.initials: M
authors.lastname: Schuster
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D018441:Biofilms / Q000254:growth & development*; D015964:Gene Expression Regulation, Bacterial; D005816:Genetic Complementation Test; D016296:Mutagenesis; D011135:Polysaccharides, Bacterial / Q000378:metabolism; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000254:growth & development*; D015363:Quinolones / Q000378:metabolism*; D053038:Quorum Sensing; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; C080365:LasR protein, Pseudomonas aeruginosa; D011135:Polysaccharides, Bacterial; D015363:Quinolones; D015534:Trans-Activators; C064841:exopolysaccharide, Pseudomonas