Rapidly evolving changes and gene loss associated with host switching in Corynebacterium pseudotuberculosis

Abstract

Phylogenomics and genome scale positive selection analyses were performed on 29 Corynebacterium pseudotuberculosis genomes that were isolated from different hosts, including representatives of the Ovis and Equi biovars. A total of 27 genes were identified as undergoing adaptive changes. An analysis of the clades within this species and these biovars, the genes specific to each branch, and the genes responding to selective pressure show clear differences, indicating that adaptation and specialization is occurring in different clades. These changes are often correlated with the isolation host but could indicate responses to some undetermined factor in the respective niches. The fact that some of these more-rapidly evolving genes have homology to known virulence factors, antimicrobial resistance genes and drug targets shows that this type of analysis could be used to identify novel targets, and that these could be used as a way to control this pathogen.

Fig 1. Target groups (foreground branches) 1 to 6 of a Corynebacterium pseudotuberculosis phylogeny.

Fig 2. Target groups (foreground branches) 7 and 8 of a Corynebacterium pseudotuberculosis phylogeny excluding the Equi strains 262, I37 and 162.

Fig 3. Circular map showing the position of pathogenicity islands and positively selected genes in relation to Corynebacterium pseudotuberculosis strain 31 genome.

PAI–Pathogenicity Island, PS–positively selected, CDS–coding sequences.

Fig 4. Genome variations in different branches of Corynebacterium pseudotuberculosis.

HGT–horizontal gene transfer, PS–positive selection.