Phage infection restores PQS signaling and enhances growth of a Pseudomonas aeruginosa lasI quorum-sensing mutant

Abstract

Bacteriophage (phage) therapy is reemerging as a valuable tool to combat multidrug resistant bacteria. A major hurdle in developing efficacious bacteriophage therapies is that bacteria acquire resistance to phage killing. In this context, it is noteworthy that quorum sensing (QS), the bacterial cell-to-cell communication mechanism that promotes collective undertaking of group behaviors including anti-phage defenses, enhances bacterial survival in the face of phage attack. QS relies on the production, release, accumulation, and detection of signal molecules called autoinducers. In the opportunistic pathogen Pseudomonas aeruginosa, the LasI/R QS system induces the RhlI/R QS system, and these two systems control, in opposing manners, the PQS QS system that relies on the autoinducer called PQS. A {Delta}lasI mutant is impaired in PQS synthesis, leading to accumulation of the precursor molecule HHQ. HHQ suppresses growth of the P. aeruginosa {Delta}lasI strain. We uncover a phage infection-induced mechanism that restores expression of the pqsH gene in the P. aeruginosa {Delta}lasI QS mutant. PqsH converts HHQ into PQS, preventing HHQ-mediated growth inhibition. Thus, phage-infected P. aeruginosa {Delta}lasI cells exhibit superior growth compared to uninfected cells. Phage infection also restores expression of virulence factors and the CRISPR-cas anti-phage defense system in the P. aeruginosa {Delta}lasI strain. This study highlights a challenge for phage therapy, namely that phage infection may make particular bacterial strains faster growing, more virulent, and resistant to phage killing. ImportanceThe emergence of multidrug resistant bacteria necessitates development of new antimicrobial therapies. Phage therapy relies on exploiting phages, natural enemies of bacteria, in the fight against pathogenic bacteria. For successful phage therapy development, potent phages that exhibit low propensity for acquisition of bacterial resistance are desired. Here, we show that phage infection restores QS, a cell-to-cell communication mechanism in a P. aeruginosa QS mutant, which increases its virulence and resistance to phage killing. Importantly, clinical isolates of P. aeruginosa frequently harbor mutations in particular QS genes. Thus, phage therapies against such P. aeruginosa strains may inadvertently increase bacterial virulence. Our study underscores the importance of characterizing phage-host interactions in the context of bacterial mutants that are relevant in clinical settings prior to selecting phages for therapy.