Comparative genomics of Rhodococcus equi virulence plasmids indicates host-driven evolution of the vap pathogenicity island

Iain MacArthur, Elisa Anastasi, Sonsiray Alvarez, Mariela Scortti, Jose Vazquez-Boland

Research output: Contribution to journalArticlepeer-review


The conjugative virulence plasmid is a key component of the Rhodococcus equi
accessory genome essential for pathogenesis. There are three host-associated virulence plasmid types: the equine pVAPA and porcine pVAPB circular variants and the linear pVAPN associated with bovine (ruminant) isolates. We recently
characterized the R. equi pangenome (Anastasi et al. 2016, GBE 8:3140-3148) and we report here the comparative analysis of the virulence plasmid genomes. Plasmids within each host-associated type were highly similar despite their diverse origins.
Variation was accounted for by scattered single nucleotide polymorphisms and short nucleotide indels, while larger indels —mostly in the plasticity region near the vap pathogencity island (PAI)— defined plasmid genomic subtypes. Only one of the
plasmids analyzed, of pVAPN type, was exceptionally divergent due to accumulation of indels in the housekeeping backbone. Each host-associated plasmid type carried a unique PAI differing in vap gene complement, suggesting animal host-specific
evolution of the vap multigene family. Complete conservation of the vap PAI was observed within each host-associated plasmid type. Both diversity of host-associated plasmid types and clonality of specific chromosomal-plasmid genomic type
combinations were observed within the same R. equi phylogenomic subclade. Our data indicate that the overall strong conservation of the R. equi host-associated virulence plasmids is the combined result of host-driven selection, lateral transfer
between strains, and geographical spread due to international livestock exchanges.
Original languageEnglish
Pages (from-to)1241-1247
JournalGenome Biology and Evolution
Issue number5
Early online date22 Mar 2017
Publication statusPublished - 1 May 2017


  • Rhodococcus equi
  • Pangenome analysis
  • Comparative genomics
  • Host-associated virulence plasmids
  • Host tropism


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