QscR, a modulator of quorum-sensing signal synthesis and virulence in Pseudomonas aeruginosa

The opportunistic pathogenic bacterium Pseudomonas aeruginosa uses quorum-s ensing signaling systems as global regulators of virulence genes. There are two quorum-sensing signal receptor and signal generator pairs, LasR-Lasl a nd RhlR-Rhll. The recently completed P. aeruginosa genome-sequencing projec t revealed a gene coding for a homolog of the signal receptors, LasR and Rh lR. Here we describe a role for this gene, which we call qscR. The qscR gen e product governs the timing of quorum-sensing-controlled gene expression a nd it dampens virulence in an insect model. We present evidence that sugges ts the primary role of QscR is repression of lasl. A qscR mutant produces t he Lasl-generated signal prematurely, and this results in premature transcr iption of a number of quorum-sensing-regulated genes. When fed to Drosophil a melanogaster, the qscR mutant kills the animals more rapidly than the par ental P. aeroginosa. The repression of lasl by QscR could serve to ensure t hat quorum-sensing-controlled genes are not activated in environments where they are not useful.