Abstract:PcoI-PcoR is a quorum-sensing (QS) system influencing the biofilm formation and rhizosphere colonization in Pseudomonas fluorescens 2P24. The expression of the pcoI, a N-acyl-homoserne lactone (AHL) biosynthase gene, is under the regulation of a number of chromosomal factors, such as the GacS-GacA two-component system. In this paper, we investigated the upstream regulators that influence the transcription of pcoI gene using a chromosomal pcoI-lacZ fusion reporter strain PM203. Cosmids containing genomic DNA of the wild-type strain 2P24 were introduced into the reporter strain PM203 (gacA—, pcoI-lacZ) to screen positive transcriptional regulators of pcoI gene. One of them named pP32-24, which contained a 5-kb Pst I functional fragment was selected. Further analysis identified that the pcoI was the gene responsible for the increase of the pcoI-lacZ expression. The expression of pcoI-lacZ reporter was also improved in both PM101 (pcoI-lacZ) and its gacA- mutant PM203 after addition of exogenous AHL, indicating that the expression of pcoI is positively regulated by AHL (autoinduction) in strain 2P24. In addition, deletion mutagenesis and complementation experiments demonstrated that the transcriptional regulator PcoR positively controlled the expression of pcoI and the formation of biofilm. These results suggest that, in strain 2P24, the expression of PcoI-PcoR QS system is auto-inducted, and the transcriptional factor PcoR is involved in the regulation of pcoI transcription and the biofilm formation.
