REGULATION OF THE XCP SECRETION PATHWAY BY MULTIPLE QUORUM-SENSING MODULONS IN PSEUDOMONAS-AERUGINOSA

The virulence of the opportunistic pathogen Pseudomonas aeruginosa is largely dependent upon the extracellular production of a number of sec reted proteins with toxic or degradative activities, The synthesis of several exoenzymes is controlled in a cell-density-dependent manner by two interlinked quorum-sensing systems. Their secretion across the ou ter membrane occurs through the Xcp translocation machinery. The rep l ocus located at 40 min on the chromosome consists of two divergently t ranscribed operons, namely xcpPQ and xcpR to xcpZ, In this study, tran scriptional fusions were constructed between the xcpP and xcpR genes a nd the lacZ reporter, Transcriptional activation of the xcpP and xcpR genes in P aeruginosa is growth-phase dependent and the lasR-lasi auto induction system is required for this control, In the heterologous hos t Escherichia coli, the lasR gene product, together with its cognate a utoinducer N-(3-oxododecanoyl)-L-homoserine lactone (OdDHL), activates both the xcpP-lacZ and the xcpR-lacZ gene fusion. The second P. aerug inosa quorum-sensing modulon rhlR-rhll (vsmR-vsml) is also involved in the control of the rep genes. Expression of the lacZ fusions is stron gly reduced in PANO67, a pleiotropic mutant defective in the productio n of N-acyl-homoserine lactones responsible for the activation of RhlR , Furthermore, introduction of the lasR mutation in PANO67 results in additional diminution of xcpR transcription, indicating that the two s ystems can regulate their target genes independently, These data demon strate that expression of the rep secretion system depends on a comple x regulatory network involving cell-cell signalling which controls pro duction and secretion of virulence-associated factors.