Regulation of quorum sensing by RpoS in Pseudomonas aeruginosa

The LasR-LasI and RhlR-RhlI quorum-sensing systems are global regulators of gene expression in the opportunistic pathogen Pseudomonas aeruginosa. Prev ious studies suggest that the RhlR-RhlI system activates expression of rpoS . We constructed merodiploid strains of P. aeruginosa containing the native rpoS gene and an rpob-lan fusion. Studies of lacZ transcription in these s trains indicated that rpoS was not regulated by RhlR-RhlI. We also generate d an rpoS null mutant. This rpoS mutant showed elevated levels of rhlI (but not rhlR) transcription, elevated levels of the RhlI-generated acylhomoser ine lactone quorum-sensing;signaI, and elevated levels of RhlR-RhlI-regulat ed gene transcription. These findings indicate that there is a relationship between RpoS and quorum sensing, but rather than the RhlR-RhlI system infl uencing the expression of rpoS, it appears that RpoS regulates rhlI.