Genomic acquisition of a capsular polysaccharide virulence cluster by non-pathogenic Burkholderia isolates.
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.
Sim
Bernice Meng Qi
BM
Genome Institute of Singapore, 60 Biopolis Street, 138672 Singapore. simb@gis.a-star.edu.sg
Chantratita
Narisara
N
Ooi
Wen Fong
WF
Nandi
Tannistha
T
Tewhey
Ryan
R
Wuthiekanun
Vanaporn
V
Thaipadungpanit
Janjira
J
Tumapa
Sarinna
S
Ariyaratne
Pramila
P
Sung
Wing-Kin
WK
Sem
Xiao Hui
XH
Chua
Hui Hoon
HH
Ramnarayanan
Kalpana
K
Lin
Chi Ho
CH
Liu
Yichun
Y
Feil
Edward J
EJ
Glass
Mindy B
MB
Tan
Gladys
G
Peacock
Sharon J
SJ
Tan
Patrick
P
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
D011135:Polysaccharides, Bacterial
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