title: Transcriptome reprogramming by plasmid-encoded transcriptional regulators is required for host niche adaption of a macrophage pathogen.
abstract: Rhodococcus equi is a facultative intracellular pathogen of macrophages, relying on the presence of a conjugative virulence plasmid harboring a 21-kb pathogenicity island (PAI) for growth in host macrophages. The PAI encodes a family of 6 virulence-associated proteins (Vaps) in addition to 20 other proteins. The contribution of these to virulence has remained unclear. We show that the presence of only 3 virulence plasmid genes (of 73 in total) is required and sufficient for intracellular growth. These include a single vap family member, vapA, and two PAI-located transcriptional regulators, virR and virS. Both transcriptional regulators are essential for wild-type-level expression of vapA, yet vapA expression alone is not sufficient to allow intracellular growth. A whole-genome microarray analysis revealed that VirR and VirS substantially integrate themselves into the chromosomal regulatory network, significantly altering the transcription of 18% of all chromosomal genes. This pathoadaptation involved significant enrichment of select gene ontologies, in particular, enrichment of genes involved in transport processes, energy production, and cellular metabolism, suggesting a major change in cell physiology allowing the bacterium to grow in the hostile environment of the host cell. The results suggest that following the acquisition of the virulence plasmid by an avirulent ancestor of R. equi, coevolution between the plasmid and the chromosome took place, allowing VirR and VirS to regulate the transcription of chromosomal genes in a process that ultimately promoted intracellular growth. Our findings suggest a mechanism for cooption of existing chromosomal traits during the evolution of a pathogenic bacterium from an avirulent saprophyte.
authors.affiliation: Department of Infectious Diseases, University of Georgia, Athens, Georgia, USA.
authors.forename: Garry B
authors.initials: GB
authors.lastname: Coulson
authors.affiliation: UCD School of Biomolecular and Biomedical Science and UCD Conway Institute, University College Dublin, Dublin, Ireland.
authors.forename: Aleksandra A
authors.initials: AA
authors.lastname: Miranda-CasoLuengo
authors.affiliation: UCD School of Biomolecular and Biomedical Science and UCD Conway Institute, University College Dublin, Dublin, Ireland.
authors.forename: Raúl
authors.initials: R
authors.lastname: Miranda-CasoLuengo
authors.affiliation: UCD School of Biomolecular and Biomedical Science and UCD Conway Institute, University College Dublin, Dublin, Ireland.
authors.forename: Xiaoguang
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Infectious Diseases, University of Georgia, Athens, Georgia, USA.
authors.forename: Jenna
authors.initials: J
authors.lastname: Oliver
authors.affiliation: Department of Infectious Diseases, University of Georgia, Athens, Georgia, USA.
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Willingham-Lane
authors.affiliation: UCD School of Biomolecular and Biomedical Science and UCD Conway Institute, University College Dublin, Dublin, Ireland wim.meijer@ucd.ie hondalus@uga.edu.
authors.forename: Wim G
authors.initials: WG
authors.lastname: Meijer
authors.affiliation: Department of Infectious Diseases, University of Georgia, Athens, Georgia, USA wim.meijer@ucd.ie hondalus@uga.edu.
authors.forename: Mary K
authors.initials: MK
authors.lastname: Hondalus
mesh_terms: D000193:Actinomycetales Infections / Q000382:microbiology*; D000222:Adaptation, Physiological; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D008264:Macrophages / Q000382:microbiology*; D051379:Mice; D010957:Plasmids / Q000235:genetics* / Q000378:metabolism; D016929:Rhodococcus equi / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D014158:Transcription, Genetic; D059467:Transcriptome; D037521:Virulence Factors / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D037521:Virulence Factors