Role of the Pseudomonas aeruginosa las and rhl quorum-sensing systems in rhlI regulation

In Pseudomonas aeruginosa the LasR-LasI and RhlR-RhlI quorum-sensing (QS) systems control expression of numerous virulence genes in a population density-dependent fashion. In this study, we investigated regulation of the autoinducer synthase gene rhlI, which is responsible for C-4-HSL signal production. Primer extension analysis was used to map the rhlI transcriptional start site and an upstream regulatory region was identified. Expression studies revealed that (i) this regulatory region is important for rhlI expression and (ii) although the rhl QS system will induce rhlI, las is the dominant regulator. Furthermore, we found that control of rhlI in Escherichia coli is markedly different than in P. aeruginosa. (C) 2002 Published by Elsevier Science B.V. on behalf of the Federation of European Microbiological Societies.