title: Type VI secretion is a major virulence determinant in Burkholderia mallei.
abstract: Burkholderia mallei is a host-adapted pathogen and a category B biothreat agent. Although the B. mallei VirAG two-component regulatory system is required for virulence in hamsters, the virulence genes it regulates are unknown. Here we show with expression profiling that overexpression of virAG resulted in transcriptional activation of approximately 60 genes, including some involved in capsule production, actin-based intracellular motility, and type VI secretion (T6S). The 15 genes encoding the major sugar component of the homopolymeric capsule were up-expressed > 2.5-fold, but capsule was still produced in the absence of virAG. Actin tail formation required virAG as well as bimB, bimC and bimE, three previously uncharacterized genes that were activated four- to 15-fold when VirAG was overproduced. Surprisingly, actin polymerization was found to be dispensable for virulence in hamsters. In contrast, genes encoding a T6S system were up-expressed as much as 30-fold and mutations in this T6S gene cluster resulted in strains that were avirulent in hamsters. SDS-PAGE and mass spectrometry demonstrated that BMAA0742 was secreted by the T6S system when virAG was overexpressed. Purified His-tagged BMAA0742 was recognized by glanders antiserum from a horse, a human and mice, indicating that this Hcp-family protein is produced in vivo during infection.
authors.affiliation: Department of Microbiology, University of Georgia, Athens, GA 30602, USA.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Schell
authors.forename: Ricky L
authors.initials: RL
authors.lastname: Ulrich
authors.forename: Wilson J
authors.initials: WJ
authors.lastname: Ribot
authors.forename: Ernst E
authors.initials: EE
authors.lastname: Brueggemann
authors.forename: Harry B
authors.initials: HB
authors.lastname: Hines
authors.forename: Dan
authors.initials: D
authors.lastname: Chen
authors.forename: Lyla
authors.initials: L
authors.lastname: Lipscomb
authors.forename: H Stanley
authors.initials: HS
authors.lastname: Kim
authors.forename: Jan
authors.initials: J
authors.lastname: Mrázek
authors.forename: William C
authors.initials: WC
authors.lastname: Nierman
authors.forename: David
authors.initials: D
authors.lastname: Deshazer
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D042726:Burkholderia mallei / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D002460:Cell Line; D006224:Cricetinae; D005260:Female; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D005896:Glanders / Q000382:microbiology* / Q000401:mortality; D006736:Horses; D006801:Humans; D008264:Macrophages / Q000382:microbiology; D008647:Mesocricetus; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D005810:Multigene Family; D020411:Oligonucleotide Array Sequence Analysis; D015398:Signal Transduction; D014774:Virulence
chemical_list: D001426:Bacterial Proteins