Type VII secretion in Bacillus anthracis.

摘要

Specialized secretion systems in bacteria are uniquely evolved for the conditional introduction of effectors into the extracellular environment independent of the general secretory (Sec) pathway. These secretion machines are employed by bacteria to achieve aims particular to a given niche or pathogenic attribute. One such system, designated Type VII secretion, is distinct in its restriction to Gram-positive bacteria. Type VII secretion systems export WXG100 proteins; six such proteins identified in Bacillus anthracis genome have been designated EsxB, EsxL, EsxP, EsxQ, EsxW, and EsxV. We report detection of EsxB and EsxW in culture supernatants, demonstrating functional secretion in this organism. In this dissertation investigations of EsxB and EsxW secretion requirements and mechanism are undertaken in an attempt to understand the biology of this system and its contribution to the anthrax life cycle. In B. anthracis, we observe complex regulation of WXG100 substrate expression and secretion, distinct domain architecture in some substrates, and dynamic WXG100 substrate interactions divergent from other investigated Type VII secretion systems. In addition, the lack of conserved genetic requirements for secretion suggests that both the mechanism and the translocation machinery through which these WXG100 proteins are secreted is not conserved when compared to the prototypical Type VII secretion system, Mycobacterium tuberculosis ESX-1. On the other hand, the WXG100 protein EsxB is shown here to maintain structural features found for those of M. tuberculosis and Staphylococcus aureus, suggesting functional conservation.;As Type VII pathway genes are found in pathogenic and non-pathogenic bacteria occupying a range of environments, we propose that WXG100 proteins may represent structural and/or regulatory substrates of a highly adaptable secretion mechanism utilized to diverse ends in Gram-positive organisms, perhaps by facilitating the export of hitherto unidentified effectors unique to each organism. Future experimentation will seek to ascertain the utility of WXG100 export in B. anthracis and the secretion portal which supports their egress.;Further, in the course of this investigation, two proteins designated BepA and BepB are observed to have an extracellular topology that cannot be rationalized within our current knowledge of B. anthracis protein secretion. Work presented within this dissertation highlights the utilization of specialized secretion systems in B. anthracis. Further investigation of how B. anthracis takes advantage of non-classical secretion for the regulated and particular introduction of effectors into its environment will better our understanding of the complex biology that culminates in anthrax disease.