title: Genomic acquisition of a capsular polysaccharide virulence cluster by non-pathogenic Burkholderia isolates.
abstract: BACKGROUND
  Burkholderia thailandensis is a non-pathogenic environmental saprophyte closely related to Burkholderia pseudomallei, the causative agent of the often fatal animal and human disease melioidosis. To study B. thailandensis genomic variation, we profiled 50 isolates using a pan-genome microarray comprising genomic elements from 28 Burkholderia strains and species.
  
  
  RESULTS
  Of 39 genomic regions variably present across the B. thailandensis strains, 13 regions corresponded to known genomic islands, while 26 regions were novel. Variant B. thailandensis isolates exhibited isolated acquisition of a capsular polysaccharide biosynthesis gene cluster (B. pseudomallei-like capsular polysaccharide) closely resembling a similar cluster in B. pseudomallei that is essential for virulence in mammals; presence of this cluster was confirmed by whole genome sequencing of a representative variant strain (B. thailandensis E555). Both whole-genome microarray and multi-locus sequence typing analysis revealed that the variant strains formed part of a phylogenetic subgroup distinct from the ancestral B. thailandensis population and were associated with atypical isolation sources when compared to the majority of previously described B. thailandensis strains. In functional assays, B. thailandensis E555 exhibited several B. pseudomallei-like phenotypes, including colony wrinkling, resistance to human complement binding, and intracellular macrophage survival. However, in murine infection assays, B. thailandensis E555 did not exhibit enhanced virulence relative to other B. thailandensis strains, suggesting that additional factors are required to successfully colonize and infect mammals.
  
  
  CONCLUSIONS
  The discovery of such novel variant strains demonstrates how unbiased genomic surveys of non-pathogenic isolates can reveal insights into the development and emergence of new pathogenic species.
authors.affiliation: Genome Institute of Singapore, 60 Biopolis Street, 138672 Singapore. simb@gis.a-star.edu.sg
authors.forename: Bernice Meng Qi
authors.initials: BM
authors.lastname: Sim
authors.forename: Narisara
authors.initials: N
authors.lastname: Chantratita
authors.forename: Wen Fong
authors.initials: WF
authors.lastname: Ooi
authors.forename: Tannistha
authors.initials: T
authors.lastname: Nandi
authors.forename: Ryan
authors.initials: R
authors.lastname: Tewhey
authors.forename: Vanaporn
authors.initials: V
authors.lastname: Wuthiekanun
authors.forename: Janjira
authors.initials: J
authors.lastname: Thaipadungpanit
authors.forename: Sarinna
authors.initials: S
authors.lastname: Tumapa
authors.forename: Pramila
authors.initials: P
authors.lastname: Ariyaratne
authors.forename: Wing-Kin
authors.initials: WK
authors.lastname: Sung
authors.forename: Xiao Hui
authors.initials: XH
authors.lastname: Sem
authors.forename: Hui Hoon
authors.initials: HH
authors.lastname: Chua
authors.forename: Kalpana
authors.initials: K
authors.lastname: Ramnarayanan
authors.forename: Chi Ho
authors.initials: CH
authors.lastname: Lin
authors.forename: Yichun
authors.initials: Y
authors.lastname: Liu
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Feil
authors.forename: Mindy B
authors.initials: MB
authors.lastname: Glass
authors.forename: Gladys
authors.initials: G
authors.lastname: Tan
authors.forename: Sharon J
authors.initials: SJ
authors.lastname: Peacock
authors.forename: Patrick
authors.initials: P
authors.lastname: Tan
mesh_terms: D000818:Animals; D019117:Burkholderia / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity*; D019121:Burkholderia Infections / Q000276:immunology; D049810:Genetic Speciation; D014644:Genetic Variation; D016680:Genome, Bacterial; D006801:Humans; D053858:Metabolic Networks and Pathways / Q000235:genetics; D051379:Mice; D005810:Multigene Family; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis; D014774:Virulence / Q000235:genetics
chemical_list: D011135:Polysaccharides, Bacterial
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