pseudomallei or B. mallei grown under different conditions, even though the antibodies used in their western blot experiments recognized recombinant forms of BipB and BipD. The authors concluded that these two T3SS-3 molecules must be expressed in detectable amounts

only under very specific in vitro conditions [90]. Using a gfp reporter strain, Burtnick et al recently showed that the B. mallei Type 6 Secretion System-1 (T6SS-1) gene tssE is not expressed at detectable Salubrinal mouse levels when bacteria are grown in LSLB or tissue culture medium, but is expressed upon phagocytosis of the organisms by murine macrophages [49]. The protein preparations tested in our studies were obtained from bacteria cultured on LSLB agar plates at 37°C, conditions which may not be PRN1371 supplier optimal for expression of the BoaA and BoaB proteins. Additionally, Chantratita and colleagues reported that growth of B. pseudomallei under various conditions triggers a complex adaptive process altering the expression of surface molecules [91]. This process, termed phenotypic plasticity, was correlated with changes in the morphology of B. pseudomallei colonies grown on agar plates

and appears to modulate the environmental GSK126 mw fitness, as well as virulence, of the organism. Given their surface location and likely role in virulence (i.e. adherence to host cells), it is possible that BoaA and BoaB are subject to phenotypic plasticity and are expressed in detectable amounts only under very specific in vitro conditions. In concordance, the reduced adherence phenotype of the boaA and boaB mutant strains suggests increased level of expression of the genes when Burkholderia is incubated with epithelial cells. However, efforts to detect protein expression under these conditions MTMR9 (i.e. immunofluorescence, immunoprecipitation) have been unsuccessful. Of further note, studies have shown that sera from horses infected with B. mallei and sera from melioidosis patients contain antibodies reacting with BoaA (i.e.

B. mallei ATCC23344 locus tag number BMAA0649) [81] and with BoaB (i.e. B. pseudomallei K96243 locus tag number BPLS1705)[92], respectively, which indicates expression of the autotransporters in vivo. Determining the conditions and mechanisms that modulate expression of the Boa adhesins, and their influence on the binding of B. pseudomallei and B. mallei to host surfaces, represent key areas for future study. Disruption of boaA and boaB in the B. pseudomallei double mutant strain DD503.boaA.boaB was found to have a significant effect on the growth of the organism within murine macrophages (Fig 6B). At present, it is not clear whether BoaA and BoaB play a direct role in intracellular replication. It is possible that the absence of both Boa proteins in the OM of DD503.boaA.boaB affects the proper surface display of another molecule involved in this phenotypic trait.