| Mycobacterium tuberculosis is the causative agent of tuberculosis, a respiratory disease that represents a serious threat to global health. M. tuberculosis is an intracellular pathogen that resides within the phagosome of human macrophages. Although its intracellular environment confers many advantages, including sheltering the bacteria from the host immune response, the phagosome can also be a toxic location. However, M. tuberculosis is able to survive in this environment due to its ability to produce detoxification mechanisms in response to external stimuli, as well as its ability to manipulate the host cell's formation of the phagosomal microenvironment.;Here, we present evidence that M. tuberculosis encodes mechanisms involved in the detection of copper in its environment, as well as detoxification mechanisms to prevent copper-mediated cell death. We show that M. tuberculosis specifically transcribes a set of genes in response to exposure to toxic levels of copper, including both general stress-response mechanisms as well as a copper-specific response. A key aspect of the M. tuberculosis response to copper comes from its copper-responsive induction of the cso operon. We have initiated the in-depth characterization of two genes within the cso operon. The first gene, csoR, encodes a copper-binding transcriptional regulator responsible for the copper-dependent induction of cso. The third gene in the cso operon, ctpV, encodes a copper exporter required for detoxification after prolonged exposure to toxic levels of copper. We show that mycobacterial copper response plays a role in disease pathology, as the knockout mutant DeltactpV induces reduced disease pathology relative to wild type within murine and guinea pig models of infection. Additionally, human macrophage cells infected with DeltactpV display reduced cytokine expression. We also provide evidence for a relationship between mycobacterial infection and the lessened expression of host copper response mechanisms. Further, we initiate the development of tools which will allow us to more directly measure the host and bacterial copper levels upon mycobacterial infection.;Overall, this thesis provides the first characterization of M. tuberculosis copper response, and demonstrates the relevance of this response to the in vivo lifestyle of this deadly bacterium. |
