PqsE has a conserved sequence, yet a variable impact in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is an opportunistic pathogen responsible for several acute and chronic infections. The production of many of its virulence factors is tightly regulated by three interlinked quorum sensing (QS) systems named las, rhl, and pqs. The pqs system relies on 4-hydroxy-2-alkylquinolines (HAQs) as signaling molecules to activate the transcriptional regulator MvfR (PqsR), which drives HAQ biosynthesis via the pqsABCDE operon. The final gene in this operon encodes PqsE, a multifunctional protein unique to P. aeruginosa. Beyond its thioesterase activity in HAQ biosynthesis, PqsE stabilizes RhlR, the transcriptional regulator of the rhl system, facilitating the regulation of virulence-related genes. Due to its pathogenic relevance, PqsE is considered a potential therapeutic target against P. aeruginosa infections. While the role of PqsE toward the RhlR regulon is increasingly understood in reference P. aeruginosa strains such as PA14 and PAO1, its broader relevance remains underexplored. In this study, pqsE and rhlR were found to be genetically conserved across a diverse panel of 12 P. aeruginosa strains. Phenotypic assays and metabolite quantification revealed that PqsE broadly influences virulence factors and multicellular behaviors, including pyocyanin production and biofilm formation. While the magnitude of PqsE-dependent phenotypes varied between strains, key functions were consistently maintained, underscoring both conservation and strain-specific modulation. Notably, PqsE proved essential for HAQ biosynthesis in most strains, challenging prior assumptions of its dispensability. This study contributes to a deeper understanding of QS regulation, highlighting that while PqsE contributes to conserved functions across P. aeruginosa strains, its impact is strain dependent.IMPORTANCEPseudomonas aeruginosa is a versatile opportunistic pathogen, naturally tolerant and readily acquiring resistance to multiple antibiotics. Consequently, the World Health Organization identified this bacterium as a high-priority pathogen for researching and developing new antimicrobial strategies. P. aeruginosa utilizes quorum sensing, a cell-to-cell communication system, to regulate the expression of several of its virulence factors. Here, we confirm that the PqsE protein is conserved, and its function in quorum sensing, especially toward the RhlR regulator, is variable across a panel of 12 P. aeruginosa strains. Since PqsE is conserved and unique to this bacterium, it has been proposed as an ideal target for antivirulence therapies, offering new alternatives to combat antimicrobial resistance. However, our results question the relevance of PqsE as an appropriate target.