Transcriptome of B. pseudomallei in different niches

Burkholderia pseudomallei, a Gram-negative pathogen, is the causative agent of melioidosis in humans. This bacterium can be isolated from the soil, stagnant and salt-water bodies and from human and animal clinical specimens. While extensive studies have contributed to the understanding of B. pseudomallei pathogenesis, little is known about how a harmless soil bacterium adapts when it shifts to a human host and exhibits its virulence. The bacterium's large genome encodes an array of factors that support the pathogen's ability to survive under stressful conditions, including the host internal milieu. In this study, we performed comparative transcriptome analysis of B. pseudomallei cultured in human plasma versus soil extract media to provide insights on B. pseudomallei gene expression that govern bacterial adaptation and infectivity in the host. A total of 455 genes were differentially regulated; genes up-regulated in B. pseudomallei grown in human plasma are involved in energy metabolism and cellular process whilst the down-regulated genes mostly include fatty acid and phospholipid metabolism, amino acid biosynthesis and regulatory function proteins. Further analysis identified a significant up-regulation of biofilm-related genes in plasma, which was validated using the biofilm-forming assay and scanning electron microscopy. In addition, genes encoding known virulence factors such as capsular polysaccharide and flagella were also over-expressed, suggesting an overall enhancement of B. pseudomallei virulence potential when present in human plasma. This ex vivo gene expression profile provides comprehensive information on B. pseudomallei's adaptation when shifted from the environment to the host. The induction of biofilm formation under host conditions may explain the difficulty in treating septic melioidosis.