Quorum-sensing synthase mutations re-calibrate autoinducer concentrations in clinical isolates of Pseudomonas aeruginosa to enhance pathogenesis

Quorum sensing is a mechanism of bacterial communication that controls virulence gene expression. Pseudomonas aeruginosa regulates virulence via two synthase/transcription factor receptor pairs: LasI/R and RhlI/R. LasR is considered the master transcriptional regulator of quorum sensing, as it upregulates rhlI/R . However, clinical isolates often have frequent inactivating mutations in lasR , while maintaining Rhl-dependent signaling. We sought to understand how quorum sensing progresses in isolates with lasR mutations, specifically via activation of RhlR. We found that clinical isolates with lasR inactivating mutations often harbored concurrent mutations in rhlI . Using ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry, we discovered that strains lacking lasR overproduced the RhlI-synthesized autoinducer and that RhlI variants re-calibrated autoinducer concentrations to wild-type levels, restoring virulent phenotypes. These findings provide the molecular basis for the plasticity of quorum sensing in an infection niche.