We performed comparative genomics on 66 Xanthomonas campestris pv. campestris (Xcc) strains to investigate the interplay between pathogenicity and xanthan production. Our analysis revealed an open pan-genome and a striking evolutionary dichotomy: the xanthan biosynthesis (gum) cluster is highly conserved to maintain polymer integrity, while the O-antigen (wxc) cluster is hypervariable, likely driven by immune evasion. Functional validation showed that variants of Rmd exhibit a 22-fold activity span with minimal impact on xanthan gum yield. Conversely, wxc diversity significantly influences xanthan yield via metabolic feedback without affecting viscosity. Furthermore, we demonstrated that host restriction-modification systems drive exogenous DNA instability by targeting specific methylation motifs. Site-directed mutagenesis of these motifs successfully restored plasmid stability. These findings provide a population-scale framework for Xcc evolution and offer validated strategies for overcoming barriers to genetic engineering.
Wang et al. (Wed,) studied this question.