ATP-binding cassette systems in Burkholderia pseudomallei and Burkholderia mallei.

BACKGROUND: ATP binding cassette (ABC) systems are responsible for the import and export of a wide variety of molecules across cell membranes and comprise one of largest protein superfamilies found in prokarya, eukarya and archea. ABC systems play important roles in bacterial lifestyle, virulence and survival. In this study, an inventory of the ABC systems of Burkholderia pseudomallei strain K96243 and Burkholderia mallei strain ATCC 23344 has been compiled using bioinformatic techniques. RESULTS: The ABC systems in the genomes of B. pseudomallei and B. mallei have been reannotated and subsequently compared. Differences in the number and types of encoded ABC systems in belonging to these organisms have been identified. For example, ABC systems involved in iron acquisition appear to be correlated with differences in genome size and lifestyles between these two closely related organisms. CONCLUSION: The availability of complete inventories of the ABC systems in B. pseudomallei and B. mallei has enabled a more detailed comparison of the encoded proteins in this family. This has resulted in the identification of ABC systems which may play key roles in the different lifestyles and pathogenic properties of these two bacteria. This information has the potential to be exploited for improved clinical identification of these organisms as well as in the development of new vaccines and therapeutics targeted against the diseases caused by these organisms.

The identification and evaluation of ATP binding cassette systems in the intracellular bacterium Francisella tularensis.

Francisella tularensis is a facultative intracellular bacterium responsible for the disease tularemia. Analysis of the fully sequenced genome of the virulent F. tularensis strain SCHU S4 has led to the identification of twenty ATP binding cassette (ABC) systems, of which five appear to be non-functional. The fifteen complete systems comprise three importers, five exporters, four systems involved in non-transport processes, and three systems of unknown or ill-defined function. The number and classification of the ABC systems in F. tularensis is similar to that observed in other intracellular bacteria, indicating that some of these systems may be important for the intracellular lifestyle of these organisms. Among the ABC systems identified in the genome are systems that may be involved in the virulence of F. tularensis SCHU S4. Six ABC system proteins were evaluated as candidate vaccine antigens against tularemia, although none provided significant protection against F. tularensis. However, a greater understanding of these systems may lead to the development of countermeasures against F. tularensis.

An association between ATP binding cassette systems, genome sizes and lifestyles of bacteria.

Comparative bioinformatic analyses of ATP binding cassette (ABC) systems encoded in bacterial genomes have been undertaken in order to examine whether the range and distribution of these systems correlates with niches occupied by different organisms. In general, bacteria with larger genomes were found to encode more ABC systems than those with smaller genomes. Environmental bacteria, generally containing the largest genomes, showed the greatest number and diversity of ABC systems. Extracellular bacteria have larger genomes and show higher relative numbers of ABC transporters in comparison to intracellular bacteria. Similar results were obtained when comparing bacteria with different respiratory requirements since aerobic bacteria have larger genomes and also display greater numbers of ABC systems than anaerobes. These results suggest that the number of ABC systems encoded in bacterial genomes correlates with genome size and also with the physiological niche in which bacteria live. Furthermore, the distribution of the ABC systems into families indicates that the process of reductive evolution is responsible for retaining particular types of ABC systems as bacteria adapt to particular niches.

Identification of a LolC homologue in Burkholderia pseudomallei, a novel protective antigen for melioidosis.

Melioidosis is an emerging disease of humans in Southeast Asia and tropical Australia. The bacterium causing this disease, Burkholderia pseudomallei, is also considered a bioterrorism agent, and as yet there is no licensed vaccine for preventing B. pseudomallei infection. In this study, we evaluated selected proteins (LolC, PotF, and OppA) of the ATP-binding cassette systems of B. pseudomallei as candidate vaccine antigens. Nonmembrane regions of the B. pseudomallei proteins were expressed and purified from Escherichia coli and then evaluated as vaccine candidates in an established mouse model of B. pseudomallei infection. When delivered with the monophosphoryl lipid A-trehalose dicorynomycolate adjuvant, the proteins stimulated antigen-specific humoral and cellular immune responses. Immunization with LolC or PotF protein domains afforded significant protection against a subsequent challenge with B. pseudomallei. The most promising vaccine candidate, LolC, provided a greater level of protection when it was administered with immune-stimulating complexes complexed with CpG oligodeoxynucleotide 10103. Immunization with LolC also protected against a subsequent challenge with a heterologous strain of B. pseudomallei, demonstrating the potential utility of this protein as a vaccine antigen for melioidosis.

The ABC transporter protein OppA provides protection against experimental Yersinia pestis infection.

The identification of Yersinia pestis as a potential bioterrorism agent and the emergence of antibiotic-resistant strains have highlighted the need for improved vaccines and treatments for plague. The aim of this study was to evaluate the potential for ATP-binding cassette (ABC) transporter proteins to be exploited as novel vaccines against plague. Western blotting of ABC transporter proteins using sera from rabbits immunized with killed whole Y. pestis cells or human convalescent-phase sera identified four immunologically reactive proteins: OppA, PstS, YrbD, and PiuA. Mice immunized with these proteins developed antibody to the immunogen. When the immunized mice were challenged with Y. pestis, the OppA-immunized mice showed an increased time to death compared to other groups, and protection appeared to correlate with the level of immunoglobulin G antibody to OppA.