Analysis of plasmid and its role in phytopathogenic bacteria Xanthomonas citri pv. viticola strains

The most significant bacterial disease infecting grape is bacterial leaf spot (BLS), caused by Xanthomonas citri pv. viticola (Xcv) strain. In the field, BLS severity depends on host genotype, pathogen pressure and environmental conditions. Plasmids, the extra chromosomal DNA components of phytopathogenic bacteria, play a crucial role in disease development as well as in the diverse evolution of the pathogen. Genome diversity and distribution of genes responsible for various factors present on plasmid in the pathogen are not well understood. The current research aimed to investigate various plasmid-borne traits in Xcv strains collected from twenty-three different locations. Four different curing agents viz. ethidium bromide (EtBr), acridine orange (AO), sodium dodecyl sulphate (SDS) and elevated heat were used to cure the plasmid. The findings revealed uniform plasmid size of approximately 23 kb among all isolates of India. The study also reveals the effect of plasmid curing on various traits, including morphology, pathogenicity, exopolysaccharide production, and antibiotic sensitivity. Exopolysaccharide production and pathogenicity were significantly reduced in the cured isolates. Cured Xcv isolates also exhibited significant variation in tested traits, displaying phenotypic differences in color, size, shape, elevation, appearance and margin. The study further emphasized the crucial role of plasmids as carriers for genetic exchange among plant pathogenic bacteria, contributing to bacterial adaptation to the environment. Additionally, the research highlighted the presence of antibiotic resistance traits on the plasmids and the importance of plasmid-mediated mechanisms in bacterial adaptation.