Mutation analysis of the Pseudomonas aeruginosa mvfR and pqsABCDE gene promoters demonstrates complex quorum-sensing circuitry

The LysR-type transcriptional regulator MvfR (PqsR) (multiple virulence factor regulator) plays a critical role in Pseudomonas aeruginosa pathogenicity via the transcriptional regulation of multiple quorum-sensing (QS)-regulated virulence factors. LasR activates full mvfR transcription, and MvfR subsequently activates pqsA–E expression. This study identifies and characterizes the key cis-regulatory elements through which mvfR and pqsA–E transcription is regulated in the highly virulent P. aeruginosa strain PA14. Deletion and site-directed mutagenesis indicate that: (1) LasR activates mvfR transcription by binding to a las/rhl box, CTAACAAAAGACATAG, centred at −513 bp upstream of the MvfR translational start site; and (2) RhlR represses pqsA transcription by binding to a las/rhl box, CTGTGAGATTTGGGAG, centred at −311 bp upstream of the pqsA transcriptional initiation site. Furthermore, it is shown that MvfR activates pqsA–E transcription by binding to a LysR box, TTCGGACTCCGAA, centred at −45 bp relative to the pqsA transcriptional initiation site, demonstrating that this LysR box has a critical role in the physical interaction between the MvfR protein and the pqsA promoter. These results provide new insights into the regulatory relationships between LasR and mvfR, and between MvfR/RhlR and the pqs operon, and elucidate further the complex regulation of the P. aeruginosa QS circuitry.