Differential control of the Pcol/PcoR quorum-sensing system in Pseudomonas fluorescens 2P24 by sigma factor RpoS and the GacS/GacA two-component regulatory system

A quorum-sensing (QS) locus Pcol/PcoR had been identified previously in the biological control bacterium Pseudomonas fluorescens 2P24. In this paper, we investigated the upstream regulators that influence the transcription of the N-acyl homoserine (actone (AHL) biosynthase gene pcol using a chromosomal. pcol::lacZ fusion reporter strain. Stationary sigma factor RpoS was identified as a negative regulator of QS system using a random mini-Tn5 mutant procedure. Furthermore, deletion mutagenesis and complementation experiments demonstrated that the two-component system GacS/GacA positively regulated the QS system by upregulating pcol transcription. However, compared with the gacA or gacS mutant, introduction of a second mutation of rpoS in the gacA(-) or gacS(-) background did not lead to further change in the transcriptional expression of the pcol gene or the synthesis of AHL. Our results suggest that in strain 2P24, RpoS could only play its negative regulatory role on the pcol gene under a functional GacS/GacA system background. (C) 2008 Elsevier GmbH. All rights reserved.