title: An Invertron-Like Linear Plasmid Mediates Intracellular Survival and Virulence in Bovine Isolates of Rhodococcus equi.
abstract: We report a novel host-associated virulence plasmid in Rhodococcus equi, pVAPN, carried by bovine isolates of this facultative intracellular pathogenic actinomycete. Surprisingly, pVAPN is a 120-kb invertron-like linear replicon unrelated to the circular virulence plasmids associated with equine (pVAPA) and porcine (pVAPB variant) R. equi isolates. pVAPN is similar to the linear plasmid pNSL1 from Rhodococcus sp. NS1 and harbors six new vap multigene family members (vapN to vapS) in a vap pathogenicity locus presumably acquired via en bloc mobilization from a direct predecessor of equine pVAPA. Loss of pVAPN rendered R. equi avirulent in macrophages and mice. Mating experiments using an in vivo transconjugant selection strategy demonstrated that pVAPN transfer is sufficient to confer virulence to a plasmid-cured R. equi recipient. Phylogenetic analyses assigned the vap multigene family complement from pVAPN, pVAPA, and pVAPB to seven monophyletic clades, each containing plasmid type-specific allelic variants of a precursor vap gene carried by the nearest vap island ancestor. Deletion of vapN, the predicted "bovine-type" allelic counterpart of vapA, essential for virulence in pVAPA, abrogated pVAPN-mediated intramacrophage proliferation and virulence in mice. Our findings support a model in which R. equi virulence is conferred by host-adapted plasmids. Their central role is mediating intracellular proliferation in macrophages, promoted by a key vap determinant present in the common ancestor of the plasmid-specific vap islands, with host tropism as a secondary trait selected during coevolution with specific animal species.
authors.affiliation: Microbial Pathogenesis Unit, School of Biomedical Sciences and Centre for Immunity, Infection and Evolution, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Ana
authors.initials: A
authors.lastname: Valero-Rello
authors.affiliation: Microbial Pathogenesis Unit, School of Biomedical Sciences and Centre for Immunity, Infection and Evolution, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Alexia
authors.initials: A
authors.lastname: Hapeshi
authors.affiliation: Division of Infection and Immunity, Roslin Institute, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Elisa
authors.initials: E
authors.lastname: Anastasi
authors.affiliation: Division of Infection and Immunity, Roslin Institute, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Sonsiray
authors.initials: S
authors.lastname: Alvarez
authors.affiliation: Microbial Pathogenesis Unit, School of Biomedical Sciences and Centre for Immunity, Infection and Evolution, University of Edinburgh, Edinburgh, United Kingdom Division of Infection and Immunity, Roslin Institute, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Mariela
authors.initials: M
authors.lastname: Scortti
authors.affiliation: School of Biomolecular and Biomedical Science, University College Dublin, Dublin, Ireland.
authors.forename: Wim G
authors.initials: WG
authors.lastname: Meijer
authors.affiliation: Division of Infection and Immunity, Roslin Institute, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Iain
authors.initials: I
authors.lastname: MacArthur
authors.affiliation: Microbial Pathogenesis Unit, School of Biomedical Sciences and Centre for Immunity, Infection and Evolution, University of Edinburgh, Edinburgh, United Kingdom Division of Infection and Immunity, Roslin Institute, University of Edinburgh, Edinburgh, United Kingdom Grupo de Patogenómica Bacteriana, Facultad de Veterinaria, Universidad de León, León, Spain v.boland@ed.ac.uk.
authors.forename: José A
authors.initials: JA
authors.lastname: Vázquez-Boland
mesh_terms: D000818:Animals; D002417:Cattle; D016000:Cluster Analysis; D003227:Conjugation, Genetic; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D022761:Gene Transfer, Horizontal; D005798:Genes, Bacterial; D008264:Macrophages / Q000382:microbiology*; D008807:Mice, Inbred BALB C; D050296:Microbial Viability; D008969:Molecular Sequence Data; D010802:Phylogeny; D010957:Plasmids; D016929:Rhodococcus equi / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification / Q000502:physiology*; D017422:Sequence Analysis, DNA; D017385:Sequence Homology; D014774:Virulence; D037521:Virulence Factors / Q000235:genetics
chemical_list: D004269:DNA, Bacterial; D037521:Virulence Factors