The evolutionary tale of tailocins in Pectobacterium show genus-wide homologous recombination and inversions of tail fiber genes

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Abstract

Pectobacterium species comprise globally present phytopathogens known to co-inhabit infected plants. During such co-infection, these pathogens can have cooperative and/or antagonistic interactions to prevent intrusion, dominate a niche, displace established strains, or release nutrients. The phage tail-like bacteriocins, also called tailocins, play an important role in shaping such bacterial communities because of their ability to kill closely related strains of the same species. Adopting a comparative pangenomics approach, we performed a phylogenetically structured study on the diversity and evolution of the carotovoricin, the only tailocin present in the Pectobacterium species. We discovered that the carotovoricin biosynthesis gene cluster was domesticated by the ancestor of the Pectobacterium genus, and its overall retention and purifying selection indicate its significance in bacterial community interactions. We identified differential conservation within the carotovoricin locus with exceptional variability and phylogenetic discord in the genes encoding the tail fibers, known to play a major role in host range specificity. We identified an evolutionary mechanism involving recombination-mediated exchange of these tail fiber genes across the Pectobacterium genus, which complements the existing DNA sequence inversion mechanism to achieve tailocin polymorphism. In particular, the genus-wide exchange of tail fiber locus discovered here is a novel strategy adopted by the plant pathogen.

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