Genomic acquisitions in emerging populations of Xanthomonas vasicola pv. vasculorum infecting corn in the U.S. and Argentina

Xanthomonas vasicola pv. vasculorum (Xvv) is an emerging bacterial plant pathogen that causes bacterial leaf streak on corn. First described in South Africa in 1949, reports of this bacteria have greatly increased in the past years in South America and in the U.S., where it is now present in most of the corn producing states. Phenotypic characterization showed that the emerging U.S. and South American Xvv populations may have increased virulence in corn compared to older strains. To understand the genetic mechanisms behind the increased virulence in this group, we used comparative genomics to identify gene acquisitions in Xvv genomes from the U.S. and Argentina. We sequenced 41 genomes of Xvv and the related sorghum-infecting X. vasicola pv. holcicola (Xvh). A comparison of all available X. vasicola genomes showed the phylogenetic relationships in the group and identified clusters of genes associated with the emerging Xvv populations. The newly acquired gene clusters showed evidence of horizontal transfer to Xvv and included candidate virulence factors. One cluster, in particular, corresponded to a prophage transferred from Xvh to all Xvv from Argentina and the U.S. The prophage contains putative secreted proteins, which represent candidates for virulence determinants in these populations and await further molecular characterization.