title: The Pseudomonas putida Lon protease is involved in N-acyl homoserine lactone quorum sensing regulation.
abstract: BACKGROUND
  In Pseudomonas putida and Pseduomonas aeruginosa, the similar PpuR/RsaL/PpuI and LasR/RsaL/LasI acyl homoserine lactones (AHLs) quorum sensing (QS) systems have been shown to be under considerable regulation by other global regulators. A major regulator is the RsaL protein which strongly directly represses the transcription of the P. putida ppuI and P. aeruginosa lasI AHL synthases. In this study we screened a transposon mutant bank of P. putida in order to identify if any other regulators were involved in negative regulation of AHL QS.
  
  
  RESULTS
  In our screen we identified three Tn5 mutants which displayed overproduction of AHLs in P. putida strain WCS358. Two of the mutants had a Tn5 located in the rsaL gene, whereas in one mutant the transposon was located in the lon protease gene. Lon proteases play important roles in protein quality control via degradation of misfolded proteins. It was determined that in the P. putida lon mutant, AHL levels, PpuR levels and ppuI promoter activity all increased significantly; we therefore postulated that PpuR is a target for Lon. The Lon protease had no effect on AHL production in P. aeruginosa.
  
  
  CONCLUSIONS
  The Lon protease is a negative regulator of AHL production in P. putida WCS358. The Lon protease has also been shown by others to influence AHL QS in Vibrio fischeri and Agrobacterium tumefaciens and can thus become an important regulator of AHL QS timing and regulation in bacteria.
authors.affiliation: International Centre for Genetic Engineering and Biotechnology, Padriciano, Trieste, Italy. bertani@icgeb.org <bertani@icgeb.org>
authors.forename: Iris
authors.initials: I
authors.lastname: Bertani
authors.forename: Giordano
authors.initials: G
authors.lastname: Rampioni
authors.forename: Livia
authors.initials: L
authors.lastname: Leoni
authors.forename: Vittorio
authors.initials: V
authors.lastname: Venturi
mesh_terms: D015107:4-Butyrolactone / Q000031:analogs & derivatives* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D002855:Chromatography, Thin Layer; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D015246:Deoxyribonuclease EcoRI / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D011401:Promoter Regions, Genetic / Q000235:genetics; D049070:Protease La / Q000235:genetics / Q000378:metabolism*; D016958:Pseudomonas putida / Q000235:genetics / Q000378:metabolism*; D053038:Quorum Sensing; D015183:Restriction Mapping; D017422:Sequence Analysis, DNA
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; C088386:homoserine lactone; D015246:Deoxyribonuclease EcoRI; D049070:Protease La; D015107:4-Butyrolactone