The identification and characterisation of PPIases from Burkholderia pseudomallei and Burkholderia thailandensis

Abstract

The aim of this study was to identify and characterise peptidyl-prolyl cis-trans isomerases (PPIases) from the bacterium Burkholderia pseudomallei, the causative agent of the disease melioidosis. The longer term goal was to assess their potential as vaccine candidates or antimicrobial targets. Using bioinformatic approaches, six putative FK506-binding proteins (FKBPs) proteins and three putative parvulin proteins were identified in B. pseudomallei. Of these, six were expressed and purified as recombinant proteins. The purified proteins were used to immunise BALB/c mice, with some providing protection against a subsequent B. pseudomallei infection. These proteins could therefore be proposed as potential vaccine candidates. Homologues of Mip or SurA, which are associated with virulence in other bacterial species, were identified in B. pseudomallei and closely related B. thailandensis. Recombinant Mip or SurA homologues from B. pseudomallei were shown to have characteristic PPIase enzyme activity. To evaluate the role of the Mip homologue from B. pseudomallei in virulence, an unmarked deletion mutant was constructed. The mutant had reduced intracellular survival; defects in putative virulence mechanisms and attenuated virulence in mice. To assess the role of a SurA homologue, closely related B. thailandensis was used as a model organism, with deletion of the gene resulting in defects in intracellular infection, outer membrane integrity and virulence. This indicates that PPIases from B. pseudomallei and B. thailandensis represent novel virulence determinants and potential antimicrobial targets for therapeutics against melioidosis.