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: Anette Steidle, Marie Allesen-Holm, Kathrin Riedel, Gabriele Berg, Michael Givskov, Søren Molin, Leo Eberl
• Journal: Applied and environmental microbiology (Appl Environ Microbiol) Vol. 68 Issue 12 Pg. 6371-82 (Dec 2002) ISSN: 0099-2240 [Print] United States
• PMID: 12450862 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Lactones
• Ligases
• N-acylhomoserine lactone synthase

Topics

• Amino Acid Sequence
• Base Sequence
• Biofilms
• Cloning, Molecular
• Feedback
• Genes, Bacterial (physiology)
• Lactones (metabolism)
• Ligases (genetics)
• Molecular Sequence Data
• Open Reading Frames
• Pseudomonas putida (genetics, physiology)