Isobavachalcone, a plant-derived chalcone, attenuates Pseudomonas aeruginosa pathogenicity by targeting the PqsR quorum-sensing regulator

The emergence of multidrug-resistant Pseudomonas aeruginosa has substantially compromised the efficacy of conventional antibiotics, underscoring the urgent need for novel anti-infective strategies. Anti-virulence approaches reduce pathogenicity without inhibiting growth. Quorum sensing (QS) networks regulate virulence factors in P. aeruginosa, and traditional Chinese medicine monomers are valuable resources for QS inhibitor discovery. Among the three QS systems (pqs, las, and rhl), the pqs pathway is the core regulator of multiple virulence determinants. Using a chromosomal pqsA′-lacZ reporter strain, we identified the natural chalcone isobavachalcone as a specific inhibitor of the pqs system. Isobavachalcone inhibited the pqs pathway in a concentration-dependent manner (IC₅₀ = 11.81 μg/mL) without affecting bacterial growth. It significantly reduced pyocyanin production by downregulating phz1 and phz2 expression, and suppressed swarming, swimming, and twitching motility. Genetic complementation confirmed that overexpression of PqsR completely reversed this inhibition, identifying PqsR as the primary target. Molecular docking, molecular dynamics simulations, circular dichroism, and isothermal titration calorimetry demonstrated that isobavachalcone directly binds to the ligand-binding domain of PqsR, primarily through hydrophobic interactions (Kd = 5.974 μM), inducing conformational changes in its secondary structure. Site-directed mutagenesis identified isoleucine 236 (ILE-236) as the critical residue for stable isobavachalcone–PqsR complex formation. In plant (Chinese cabbage) and animal (Caenorhabditis elegans) infection models, isobavachalcone reduced P. aeruginosa virulence. Collectively, these findings demonstrate that isobavachalcone suppresses P. aeruginosa pathogenicity by targeting the pqs pathway without inhibiting growth, providing a theoretical basis for developing novel anti-P. aeruginosa agents.