Quinolone trafficking via outer membrane vesicles in Pseudomonas aeruginosa
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Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen often infecting the lungs of individuals with the heritable genetic disease cystic fibrosis and the peritoneum of those undergoing continuous peritoneal dialysis. Often these infections are not caused by colonization with P. aeruginosa alone but instead by a consortium of pathogenic bacteria. Little is known about growth and persistence of P. aeruginosa in vivo, and less is known about the impact of coinfecting bacteria on P. aeruginosa pathogenesis and physiology. In this dissertation I used a rat dialysis membrane peritoneal model to evaluate the in vivo transcriptome of P. aeruginosa in monoculture and in coculture with Staphylococcus aureus. Monoculture results indicate that approximately 5% of all P. aeruginosa genes are differentially regulated during growth in vivo. Included in this analysis are genes important for iron acquisition and growth in lowoxygen environments. The presence of S. aureus caused decreased transcription of P. aeruginosa iron-regulated genes during in vivo coculture, indicating that the presence of S. aureus increases usable iron for P. aeruginosa in the environment. This lysis was shown to be dependent on antimicrobial quinolones produced by P. aeruginosa. I demonstrate that these quinolones are present in outer membrane vesicles (MVs). Not only were these quinolones present in MVs, but the quorum sensing molecule; 2-heptyl-3-hydroxy-4-quinolone (Pseudomonas Quinolone Signal; PQS) was also packaged into MVs and was necessary for MV formation. These findings illustrate that a prokaryote possesses a signal trafficking system with features common to those used by higher organisms and outlines a novel mechanism for delivery of a signal critical for coordinating group behaviors in P. aeruginosa. Although MVs are involved in important processes besides signaling, the molecular mechanism is unknown. To provide insight into the molecular mechanism of MV formation, I examined the interaction of PQS with bacterial lipids. In this work, I demonstrated that PQS interacts strongly with the acyl chains and 4’-phosphate of bacterial lipopolysaccharide. The results of my studies provide molecular insight into P. aeruginosa MV formation and demonstrate that quorum signals serve important non-signaling functions. Finally, I propose a model of PQSmediated MV formation where PQS interacts with specific outer membrane components to allow the necessary curvature for MV formation.