Ecological, evolutionary, and molecular mechanisms driving pyocin diversity in pseudomonas aeruginosa.

Bacteriocins are narrow-spectrum antibiotics produced in nearly all lineages of bacteria, meaning that these antimicrobials target closely related individuals. The bacteriocins of Pseudomonas aeruginosa, called pyocins, are highly prevalent and diverse in populations of this species. Laboratory studies have shown that pyocins can function to mediate the outcome of interactions, often allowing for the coexistence of multiple strains, as no one pyocin genotype is competitively superior. Although this has been demonstrated under laboratory conditions, the function of pyocins in natural settings and the ecological, evolutionary, and genetic mechanisms underlying pyocin diversity remains unclear. As such, for my dissertation, I conducted research that investigated the driving forces underlying diversity in pyocin phenotype and genotype in free-living isolates of P. aeruginosa. In Chapter II, I collected P. aeruginosa isolates from spatially structured household bathroom and kitchen sink drains to examine relationships among pyocin phenotype with spatial structure, environment of isolation, resource competition, and phylogenetic distance. I found isolates from different houses and different drain types to vary in pyocin-mediated inhibition, suggesting that dispersal limitations and environmental conditions help shape pyocin diversity. I also found that pyocin-mediated inhibition was most likely to occur between isolates that were intermediately phylogenetically related, but inhibition was not driven by resource competition. In Chapter III, I searched genome sequences of the isolates in my collection for pyocin genes to investigate the relationships between pyocin genotype and spatial structure, environment of isolation, and pyocin phenotype. I found isolates collected from bathroom sink drains to encode more pyocin genes than those collected from kitchen sink isolates, and isolates from different houses varied primarily with respect to pyocin immunity genes. These findings indicate that environment of isolation and, to a lesser extent, spatial structure contribute to differences in pyocin gene content. I found that while immunity genes and particular killing genes partially contribute to the outcome of inhibitory interactions, pyocin-mediated inhibition is a complex process likely driven by differing levels of expression, alternative mechanisms of resistance, and receptor specificity