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Burkholderia pseudomalleiis the causative agent of melioidosis, a disease endemic to regions of Southeast Asia and Northern Australia. Both humans and a range of other animal species are susceptible to melioidosis, and the production of a group 3 polysaccharide capsule in B. pseudomalleiis essential for virulence. B. pseudomalleicapsular polysaccharide (CPS) I comprises unbranched manno-heptopyranose residues and is encoded by a 34.5-kb locus on chromosome 1. Despite the importance of this locus, the role of all of the genes within this region is unclear. We inactivated 18 of these genes and analyzed their phenotype using Western blotting and immunofluorescence staining. Furthermore, by combining this approach with bioinformatic analysis, we were able to develop a model for CPS I biosynthesis and export. We report that inactivating gmhA, wcbJ, and wcbNin B. pseudomalleiK96243 retains the immunogenic integrity of the polysaccharide despite causing attenuation in the BALB/c murine infection model. Mice immunized with the B. pseudomalleiK96243 mutants lacking a functional copy of either gmhAor wcbJwere afforded significant levels of protection against a wild-type B. pseudomalleiK96243 challenge.

ABSTRACTMacrophage infectivity potentiators (Mips) are a group of virulence factors encoded by pathogenic bacteria such as Legionella, Chlamydia, and Neisseriaspecies. Mips are part of the FK506-binding protein (FKBP) family, whose members typically exhibit peptidylprolyl cis-transisomerase (PPIase) activity which is inhibitable by the immunosuppressants FK506 and rapamycin. Here we describe the identification and characterization of BPSS1823, a Mip-like protein in the intracellular pathogen Burkholderia pseudomallei. Recombinant BPSS1823 protein has rapamycin-inhibitable PPIase activity, indicating that it is a functional FKBP. A mutant strain generated by deletion of BPSS1823in B. pseudomalleiexhibited a reduced ability to survive within cells and significant attenuation in vivo, suggesting that BPSS1823 is important for B. pseudomalleivirulence. In addition, pleiotropic effects were observed with a reduction in virulence mechanisms, including resistance to host killing mechanisms, swarming motility, and protease production.