Disruption of Pseudomonas aeruginosa quorum sensing influences biofilm formation without affecting antibiotic tolerance

The opportunistic bacterial pathogen <i>Pseudomonas aeruginosa</i> is a leading cause of antimicrobial resistance-related deaths, and novel antimicrobial therapies are urgently required. <i>P. aeruginosa</i> infections are difficult to treat due to the bacterium's propensity to form biofilms, whereby cells aggregate to form a cooperative, protective structure. Autolysis, the self-killing of bacterial cells, and the bacterial cell-to-cell communication system, quorum sensing (QS), play essential roles in biofilm formation. Strains of <i>P. aeruginosa</i> that have lost the <i>lasI/R</i> QS system commonly develop in patients, and previous studies have characterized distinctive autolysis phenotypes in these strains. Yet, the underlying causes and implications of these autolysis phenotypes remain unknown. This study confirmed these autolysis phenotypes in the PA14 QS mutant strains, Δ<i>lasI</i> and Δ<i>lasR</i>, and investigated the consequences of QS loss and associated autolysis on biofilm formation and antibiotic susceptibility. QS mutants exhibited delayed biofilm formation but ultimately surpassed the wild-type (WT) in biofilm mass. However, the larger biofilm mass of the QS mutants was not reflected in higher live-cell numbers, indicating an altered biofilm structure. Nevertheless, QS mutant biofilms were not more susceptible to antibiotics than the WT. Artificial supplementation of Δ<i>lasI</i> with a QS signal molecule (autoinducer) restored the strain's QS system without the associated costs of QS, enabling Δ<i>lasI</i> to achieve higher pre-treatment and post-treatment live-cell numbers. Overall, the lack of QS functioning was not detrimental to biofilm antibiotic tolerance, though the artificial disruption of QS may reduce the advantages of QS mutants within <i>in vivo</i> mixed-strain populations. Much remains to be understood regarding the regulation and induction of the autolysis phenotypes observed in these strains, and future research to fully elucidate the control and consequences of autolysis may offer potential for novel antimicrobial therapies.