Genetic Diversity and Microevolution of Burkholderia pseudomallei in the Environment

The soil dwelling Gram-negative bacterium Burkholderia pseudomallei is the cause of melioidosis, a serious human infection that occurs in Southeast Asia and northern Australia. The purpose of this study was to evaluate the population genetic structure of B. pseudomallei in the environment. To achieve this, we undertook soil sampling and culture for the presence of B. pseudomallei in 100 equally spaced points within an area of disused land in northeast Thailand, and undertook detailed genotyping of primary plate colonies isolated from three independent sampling points. Our results demonstrated that multiple B. pseudomallei genotypes were present within a single soil sample, and that different genotypes were present at independent but nearby sampling points. The B. pseudomallei genetic population was unevenly distributed within a given sample, with a predominant genotype co-existing with several genotypes present as a minority population. We discuss the implications of this structuring of genotypic frequency in terms of micro-evolutionary dynamics and ecology, and how our results may inform future sampling strategies

Melioidosis Vaccines: A Systematic Review and Appraisal of the Potential to Exploit Biodefense Vaccines for Public Health Purposes

The designation of Burkholderia pseudomallei as a category B select agent has resulted in considerable research funding to develop a protective vaccine. This bacterium also causes a naturally occurring disease (melioidosis), an important cause of death in many countries including Thailand and Australia. In this study, we explored whether a vaccine could be used to provide protection from melioidosis. An economic evaluation based on its use in Thailand indicated that a vaccine could be a cost-effective intervention if used in high-risk populations such as diabetics and those with chronic kidney or lung disease. A literature search of vaccine studies in animal models identified the current candidates, but noted that models failed to take account of the common routes of infection in natural melioidosis and major risk factors for infection, primarily diabetes. This review highlights important areas for future research if biodefence-driven vaccines are to play a role in reducing the global incidence of melioidosis

FhuA Barrel-Cork Hybrids Are Active Transporters and Receptors

The crystal structure of Escherichia coli FhuA reveals a β-barrel domain that is closed by a globular cork domain. It has been assumed that the proton motive force of the cytoplasmic membrane through the interaction of the TonB protein with the TonB box of the cork opens the FhuA channel. Yet, deletion of the cork results in an FhuA derivative, FhuAΔ5–160, that still displays TonB-dependent substrate transport and phage receptor activity. To investigate this unexpected finding further, we constructed FhuAΔ5–160 derivatives of FhuA proteins from Salmonella paratyphi B, Salmonella enterica serovar Typhimurium, and Pantoea agglomerans. The FhuAΔ5–160 proteins inserted correctly into the outer membrane, and with the exception of the P. agglomerans protein, transported ferrichrome and albomycin. FhuA hybrids consisting of the β-barrel of one strain and the cork of another strain were active and showed higher TonB-dependent ferrichrome transport rates than the corkless derivatives. Exceptions were the E. coli β-barrel/Salmonella serovar Typhimurium cork hybrid protein and the Salmonella serovar Typhimurium β-barrel/P. agglomerans cork hybrid protein, both of which were less active than the β-barrels alone. Each of the FhuA mutant proteins displayed activity for each of their ligands, except for phage T5, only when coupled to TonB. The hybrid FhuA proteins displayed a similar activity with the E. coli TonB protein as with their cognate TonB proteins. Sensitivity to phages T1, T5, and φ80, rifamycin CGP 4832, and colicin M was determined by the β-barrel, whereas sensitivity to phage ES18 and microcin J25 required both the β-barrel and cork domains. These results demonstrate that the β-barrel domain of FhuA confers activity and specificity and responds to TonB and that the cork domains of various FhuA proteins can be interchanged and contribute to the activities of the FhuA hybrids