Polymicrobial interactions between co-infecting cystic fibrosis pathogens

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ABSTRACT In nature, microorganisms are typically found in multispecies communities, however most species are studied in isolation. Polymicrobial interactions in infections affect pathogenesis by influencing nutrient availability, colonization, and antibiotic resistance. In cystic fibrosis, a disease which is plagued by persistent respiratory infections, the interactions of the bacterial pathogens Pseudomonas aeruginosa and Staphylococcus aureus affect disease severity. It is common for bacteria to sense other microbes and respond antagonistically within multispecies communities. Since P. aeruginosa frequently resides in multispecies environments and has the capacity to secrete a plethora of antimicrobials, this proposal aims to investigate such a sensing and response phenomenon between P. aeruginosa and S. aureus. It was recently discovered by our lab that P. aeruginosa senses molecules released by S. aureus, and subsequently responds by producing antimicrobials that are active against S. aureus, independent of the previously described bacterial cell wall sensing by P. aeruginosa. The proposed research will take a multi-dimensional approach to analyze the polymicrobial interactions between these co-infecting pathogens. To identify the specific S. aureus exoproducts that P. aeruginosa senses, an array of promoter-reporters will be employed to determine active molecules by fractionating S. aureus supernatant and using mass spectrometry, as well as by screening a S. aureus transposon library. The antimicrobial response by P. aeruginosa will be characterized by global transcriptional analysis using RNA-seq. Further, regulation of signaling cascades will be elucidated by Tn-seq, illuminating which genes are essential to antimicrobial production. The known and novel antimicrobials induced by this interspecies sensing will be determined by biochemical fractionation, identification of the active fractions with antimicrobial activity, and mass spectrometry. Due to a surge in antibiotic resistance in both P. aeruginosa and S. aureus, and the effect of these two pathogens on cystic fibrosis disease outcomes, it is imperative to elucidate the interactions between these co-infecting pathogens. This work will yield new insight into interbacterial communication, and reveal the molecular mechanisms governing antimicrobial production pathways that could be novel targets for the development of therapeutics for chronic bacterial infections.