Genomic Correlates of Tailocin Sensitivity in Pseudomonas syringae

Phage derived bacteriocins, also referred to as tailocins, are structures encoded by bacterial genomes and deployed into the extracellular environment to target and kill sensitive cells. Tailocins display great potential as agricultural antimicrobials due to their durability, efficiency, and specificity of killing with prophylactic application of these molecules having been shown to prevent infection by multiple phytopathogens. Although previous reports have strongly suggested that tailocins of Pseudomonas syringae bind sugar moieties in the LipoPolySaccharide (LPS) of target cells, the molecular mechanisms and binding interactions that enable tailocins from P. syringae to kill sensitive targets remain unclear. 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 P. syringae 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. We identify the rfbD gene as an additional genomic indicator to predict tailocin sensitivity and use this information to test tailocin interactions with unscreened strains from across phylogroups, including some in which LPS chains have been previously characterized. Overall, our results strongly support that tailocin sensitivity across P. syringae strains is largely determined by recombination events across strains that lead to differential production of either D or L-rhamnose moieties in the main LPS chain.