Whole-genome comparative analysis of Malaysian Burkholderia pseudomallei clinical isolates

Burkholderia pseudomallei, a soil-dwelling Gram-negative bacterium, is the causative agent of the endemic tropical disease melioidosis. Clinical manifestations of B. pseudomallei infection range from acute or chronic localized infection in a single organ to fulminant septicaemia in multiple organs. The diverse clinical manifestations are attributed to various factors, including the genome plasticity across B. pseudomallei strains. We previously characterized B. pseudomallei strains isolated in Malaysia and noted different levels of virulence in model hosts. We hypothesized that the difference in virulence might be a result of variance at the genome level. In this study, we sequenced and assembled four Malaysian clinical B. pseudomallei isolates, UKMR15, UKMPMC2000, UKMD286 and UKMH10. Phylogenomic analysis showed that Malaysian subclades emerged from the Asian subclade, suggesting that the Malaysian strains originated from the Asian region. Interestingly, the low-virulence strain, UKMH10, was the most distantly related compared to the other Malaysian isolates. Genomic island (GI) prediction analysis identified a new island of 23 kb, GI9c, which is present in B. pseudomallei and Burkholderia mallei, but not Burkholderia thailandensis. Genes encoding known B. pseudomallei virulence factors were present across all four genomes, but comparative analysis of the total gene content across the Malaysian strains identified 104 genes that are absent in UKMH10. We propose that these genes may encode novel virulence factors, which may explain the reduced virulence of this strain. Further investigation on the identity and role of these 104 proteins may aid in understanding B. pseudomallei pathogenicity to guide the design of new therapeutics for treating melioidosis.