Identification of a regulatory cascade controlling Type III Secretion System 3 gene expression in Burkholderia pseudomallei.

A major and critical virulence determinant of many Gram-negative bacterial pathogens is the Type III Secretion Systems (T3SS). T3SS3 in Burkholderia pseudomallei is critical for bacterial virulence in mammalian infection models but its regulation is unknown. B. pseudomallei is the causative agent of melioidosis, a potentially fatal disease endemic in Southeast Asia and northern Australia. While screening for bacterial transposon mutants with a defective T3SS function, we discovered a TetR family regulator (bspR) responsible for the control of T3SS3 gene expression. The bspR mutant exhibited significant virulence attenuation in mice. BspR acts through BprP, a novel transmembrane regulator located adjacent to the currently delineated T3SS3 region. BprP in turn regulates the expression of structural and secretion components of T3SS3 and the AraC family regulator bsaN. BsaN and BicA likely form a complex to regulate the expression of T3SS3 effectors and other regulators which in turn affect the expression of Type VI Secretion Systems (T6SS). The complete delineation of the bspR initiated T3SS regulatory cascade not only contributes to the understanding of B. pseudomallei pathogenesis but also provides an important example of how bacterial pathogens could co-opt and integrate various regulatory motifs to form a new regulatory network adapted for its own purposes.