title: Identification and characterization of an N-acylhomoserine lactone-dependent quorum-sensing system in Pseudomonas putida strain IsoF.
abstract: Recent reports have shown that several strains of Pseudomonas putida produce N-acylhomoserine lactones (AHLs). These signal molecules enable bacteria to coordinately express certain phenotypic traits in a density-dependent manner in a process referred to as quorum sensing. In this study we have cloned a genomic region of the plant growth-promoting P. putida strain IsoF that, when present in trans, provoked induction of a bioluminescent AHL reporter plasmid. Sequence analysis identified a gene cluster consisting of four genes: ppuI and ppuR, whose predicted amino acid sequences are highly similar to proteins of the LuxI-LuxR family, an open reading frame (ORF) located in the intergenic region between ppuI and ppuR with significant homology to rsaL from Pseudomonas aeruginosa, and a gene, designated ppuA, present upstream of ppuR, the deduced amino acid sequence of which shows similarity to long-chain fatty acid coenzyme A ligases from various organisms. Using a transcriptional ppuA::luxAB fusion we demonstrate that expression of ppuA is AHL dependent. Furthermore, transcription of the AHL synthase ppuI is shown to be subject to quorum-sensing regulation, creating a positive feedback loop. Sequencing of the DNA regions flanking the ppu gene cluster indicated that the four genes form an island in the suhB-PA3819 intergenic region of the currently sequenced P. putida strain KT2440. Moreover, we provide evidence that the ppu genes are not present in other AHL-producing P. putida strains, indicating that this gene cluster is so far unique for strain IsoF. While the wild-type strain formed very homogenous biofilms, both a ppuI and a ppuA mutant formed structured biofilms with characteristic microcolonies and water-filled channels. These results suggest that the quorum-sensing system influences biofilm structural development.
authors.affiliation: Department of Microbiology, TUM, D-85350 Freising, Germany.
authors.forename: Anette
authors.initials: A
authors.lastname: Steidle
authors.forename: Marie
authors.initials: M
authors.lastname: Allesen-Holm
authors.forename: Kathrin
authors.initials: K
authors.lastname: Riedel
authors.forename: Gabriele
authors.initials: G
authors.lastname: Berg
authors.forename: Michael
authors.initials: M
authors.lastname: Givskov
authors.forename: Søren
authors.initials: S
authors.lastname: Molin
authors.forename: Leo
authors.initials: L
authors.lastname: Eberl
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D018441:Biofilms; D003001:Cloning, Molecular; D005246:Feedback; D005798:Genes, Bacterial / Q000502:physiology*; D007783:Lactones / Q000378:metabolism*; D008025:Ligases / Q000235:genetics*; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D016958:Pseudomonas putida / Q000235:genetics* / Q000502:physiology
chemical_list: D007783:Lactones; D008025:Ligases; C449816:N-acylhomoserine lactone synthase