Investigating Plasmid Diversity in Xanthomonas euvesicatoria pv. perforans Population

Plasmids are key drivers of horizontal gene transfer. These genetic elements promote diversification and rapid adaptation of bacterial populations to changing environments by transferring beneficial traits within and between bacterial species. Xanthomonas euvesicatoria pv. perforans is a devastating plant pathogen that causes bacterial spot disease in tomato and pepper. The pathogen population in Florida contains several distinct genetic lineages that differ in relative frequency. The objective of this study was to characterize plasmid diversity and gene content and plasmid distribution in relation to chromosomal phylogeny. Our in silico-based plasmid prediction revealed the presence of diverse plasmids ranging from approximately 16 to 235 kb. A network approach based on shared k-mer content uncovered 10 distinct plasmid groups with high genetic similarity (cliques). Interestingly, these plasmid cliques were confined to specific phylogenetic clusters, suggesting potential incompatibility or restricted plasmid movement between clusters. Some of the predicted plasmids carry virulence genes coding for type III secretion effectors, including transcription activator-like effectors and genes related to biocide resistance, such as copper. We also identified gene reshuffling between the plasmids, likely carried out by transposons present within them. Overall, these results provide foundational insights into plasmid diversity in X. euvesicatoria pv. perforans with implications for the role of these mobile genetic elements in genome dynamics and pathogen adaptation.