Regulation of Burkholderia pseudomallei Virulence Gene Expression: Role of PhoBR System

Burkholderia pseudomallei is the causative agent of melioidosis, a potentially lethal, tropical disease characterized by abscess formation in human internal organs.  Little is known about the regulation of virulence gene expression in this bacterium.  The goal of this study is to characterize the role of the PhoBR phosphate-responsive regulatory system in virulence gene regulation and its global regulatory functions.  phoB deletion and overexpression mutant strains were constructed in B. pseudomallei via allelic exchange procedure.  B. pseudomallei has the ability to infect macrophages and form plaques on a macrophage monolayer; however, PhoBR is not involved in this aspect of B. pseudomallei pathogenicity as the phoB deletion and overexpression strains were wild-type in plaque forming efficiency.  Burkholderia thailandensis was used as a surrogate for B. pseudomallei to determine phosphate-limiting growth conditions to be below 200 μM.  While final cell densities correlated with phosphate limitations, the generation time was not affected.  DNA microarray analysis is underway to identify PhoBR-regulated genes under phosphate-limiting and non-limiting conditions.  Study of the relationship between PhoBR and virulence may contribute to an increased understanding of B. pseudomallei pathogenesis which may be exploited for antimicrobial and vaccine development.