Genomic correlates of tailocin sensitivity in <i>Pseudomonas syringae</i>

Phage-derived bacteriocins, also referred to as tailocins, are structures encoded by bacterial genomes and deployed into the extracellular environment to kill sensitive cells. Tailocins display great potential as agricultural antimicrobials due to their durability, efficiency, and specificity of killing with prophylactic application demonstrated to prevent infection by multiple phytopathogens. Previous reports suggest that tailocins of Pseudomonas syringae interact with sugar moieties in the lipopolysaccharide (LPS) to target sensitive cells. However, it remains unclear how genetic and genomic variation at loci encoding LPS biosynthesis influences tailocin resistance and/or sensitivity across the species. We therefore carried out a genome-wide association study investigating tailocin sensitivity across a diverse set of P. syringae genomes. Our results demonstrate that genes strongly correlated with tailocin sensitivity are localized to one contiguous region on the chromosome encoding LPS structures similar to the common polysaccharide antigen of P. aeruginosa. We further find that enzymes involved in the biosynthesis and transport of D-rhamnose and L-rhamnose are associated with tailocin sensitivity classes A and B, respectively, with large-scale recombination of the O-antigen biosynthesis region likely underlying rapid and fundamental changes in LPS structure between strains. Building on these results, we identify rfbD as a genomic indicator for predicting tailocin sensitivity and use this information to test tailocin interactions with previously unscreened strains, including some in which LPS chains have been characterized. Overall, our results strongly support that tailocin sensitivity for P. syringae is broadly determined by recombination events across strains that leads to differential production of either d or L-rhamnose moieties in the main O-antigen chain.