Understanding the dynamics of Pseudomonas syringae tailocin targeting allows for predictive protective microbial inoculation of Actinidia chinensis

The Pseudomonas syringae complex is an important group within the Gammaproteobacteria and comprises several pathovars of agricultural significance. Genome mining of the P. syringae species complex has uncovered high-molecular-weight phage tail complexes termed tailocins. Tailocins exert specific bactericidal action against both closely and more distantly related bacteria and significantly shape the ecology of the microbiome. Tailocin targeting specificity is currently understood to be dependent on tail-fibers (TFs) binding to specific molecular epitopes, including lipopolysaccharide (LPS) as a bacterial cell surface receptor for tailocin TF-targeting domains. Recent work in P. syringae has strongly correlated variation at the common polysaccharide antigen of LPS with tailocin sensitivity. Here we provide biochemical evidence for LPS as the major receptor for P. syringae tailocins; examine the mechanisms and genetic basis of tailocin TF targeting; and predict strains that can provide protective colonization of plants. We then use the understanding of these mechanisms that determine the tailocin targeting spectrum and genetic knockouts and complementation to modify the bacterial canker pathogen of kiwifruit plants to predict LPS-mediated tailocin targeting by naturally occurring host microbiota, and then demonstrate the efficacy of these applied microbiome-derived tailocin-carrying commensal strains as biocontrol agents.