Copper is a required micronutrient that is also toxic at excess concentrations. Currently, little is known about the role of copper in interactions between bacterial pathogens and their human hosts. In this study, we elucidate a mechanism for copper homeostasis in the human pathogen Mycobacterium tuberculosis via characterization of a putative copper exporter, CtpV. CtpV was shown to be required by M. tuberculosis to maintain resistance to copper toxicity. Furthermore, the deletion of ctpV resulted in a 98-gene transcriptional response, which elucidates the increased stress experienced by the bacteria in the absence of this detoxification mechanism. Interestingly, although the ΔctpV mutant survives close to the wild-type levels in both murine and guinea pig models of tuberculosis, animals infected with the ΔctpV mutant displayed decreased lung damage, and mutant-infected mice had a reduced immune response to the bacteria as well as a significant increase in survival time relative to mice infected with wild-type M. tuberculosis. Overall, our study provides the first evidence for a connection between bacterial copper response and the virulence of M. tuberculosis, supporting the hypothesis that copper response could be important to intracellular pathogens, in general.

Copper (Cu) is a required micronutrient, but it is highly toxic at high concentrations. Therefore, the levels of Cu must be tightly regulated in all living cells. The phagosome of Mycobacterium tuberculosis has been shown to have variable levels of Cu. Previously, we showed that M. tuberculosis contains a copper-sensitive operon, cso , that is induced during early infection in mice. In this study, we showed that ctpV , a gene in the cso operon, is a copper-responsive gene and most likely encodes an efflux pump for Cu. Furthermore, the transcription of key genes in the cso operon is induced by Cu ions and not by other ions, such as Ni and Zn ions. To elucidate copper-responsive genes other than those in the cso operon, we utilized DNA microarrays to profile mycobacterial responses to physiological levels of Cu. A transcriptome analysis identified a novel set of 30 copper-responsive genes in M. tuberculosis , one-half of which were induced only when toxic levels of Cu were added. Interestingly, several transcriptional regulators, including the furA gene, were induced during toxic Cu exposure, indicating that there was a generalized response to oxidative stressors rather than a Cu-specific response. In general, the Cu-induced transcriptome generated should help elucidate the role of the Cu response in maintaining M. tuberculosis survival during infection and could provide novel targets for controlling this virulent pathogen.

Chronic tuberculosis represents a major health problem for one-third of the world's population today. A key question relevant to chronic tuberculosis is the physiological status of Mycobacterium tuberculosis during this important stage of infection. To examine the molecular bases of chronic tuberculosis and the role of host immunity in mycobacterial growth, we determined the mycobacterial transcriptional profiles during chronic and reactivation phases of murine tuberculosis using in vivo microarray analysis (IVMA). Following 28 days of aerosol infection, mycobacterial counts remained stable, although the bacilli were metabolically active with a 50% active transcriptome. The expression of genes involved in lipid and carbohydrate pathways was significantly enriched during the middle stage of chronic tuberculosis, suggesting a nutrient-rich microenvironment. A total of 137 genes were significantly regulated in mid-chronic tuberculosis (45 and 60 days) compared to an early stage (14 days) of infection. Additional sets of genes, including the virulence regulator virS , were up-regulated during the reactivation stage, indicating their possible roles in mycobacterial resurgence. Interestingly, a set of potential transcriptional regulators was significantly induced at the late stage of chronic tuberculosis. Bioinformatic analysis identified a large number of genes that could be regulated by one of the potential transcriptional regulators encoded by rv0348, including the sigF operon. Taken together, IVMA provided a better definition of the transcriptional machinery activated during chronic and reactivation stages of tuberculosis and identified a novel transcriptional regulator. A similar approach can be adopted to study key stages of intracellular pathogens.

Infection withMycobacterium aviumsubsp.paratuberculosiscauses Johne's disease in cattle and is a serious problem for the dairy industry worldwide. Development of models to mimic aspects of Johne's disease remains an elusive goal because of the chronic nature of the disease. In this report, we describe a surgical approach employed to characterize the very early stages of infection of calves withM. aviumsubsp.paratuberculosis. To our surprise, strains ofM. aviumsubsp.paratuberculosiswere able to traverse the intestinal tissues within 1 h of infection in order to colonize distant organs, such as the liver and lymph nodes. Both the ileum and the mesenteric lymph nodes were persistently infected for months following intestinal deposition ofM. aviumsubsp.paratuberculosisdespite a lack of fecal shedding of mycobacteria. During the first 9 months of infection, humoral immune responses were not detected. Nonetheless, using flow cytometric analysis, we detected a significant change in the cells participating in the inflammatory responses of infected calves compared to cells in a control animal. Additionally, the levels of cytokines detected in both the ileum and the lymph nodes indicated that there were TH1-type-associated cellular responses but not TH2-type-associated humoral responses. Finally, surgical inoculation of a wild-type strain and a mutantM. aviumsubsp.paratuberculosisstrain (with an inactivatedgcpEgene) demonstrated the ability of the model which we developed to differentiate between the wild-type strain and a mutant strain ofM. aviumsubsp.paratuberculosisdeficient in tissue colonization and invasion. Overall, novel insights into the early stages of Johne's disease were obtained, and a practical model of mycobacterial invasiveness was developed. A similar approach can be used for other enteric bacteria.

Johne's disease, caused byMycobacterium paratuberculosisinfection, is a worldwide problem for the dairy industry and has a possible involvement in Crohn's disease in humans. To identify virulence determinants of this economically important pathogen, a library of 5,060 transposon mutants was constructed using Tn5367insertion mutagenesis, followed by large-scale sequencing to identify disrupted genes. In this report, 1,150 mutants were analyzed and 970 unique insertion sites were identified. Sequence analysis of the disrupted genes indicated that the insertion of Tn5367was more prevalent in genomic regions with G+C content (50.5 to 60.5%) lower than the average G+C content (69.3%) of the rest of the genome. Phenotypic screening of the library identified disruptions of genes involved in iron, tryptophan, or mycolic acid metabolic pathways that displayed unique growth characteristics. Bioinformatic analysis of disrupted genes identified a list of potential virulence determinants for further testing with animals. Mouse infection studies showed a significant decrease in tissue colonization by mutants with a disruption in thegcpE,pstA,kdpC,papA2,impA,umaA1, orfabG2_2gene. Attenuation phenotypes were tissue specific (e.g., for theumaA1mutant) as well as time specific (e.g., for theimpAmutant), suggesting that those genes may be involved in different virulence mechanisms. The identified potential virulence determinants represent novel functional classes that could be necessary for mycobacterial survival during infection and could provide suitable targets for vaccine and drug development against Johne's and Crohn's diseases.

Mycobacterium tuberculosis, a pathogen infecting one third of the world population, faces numerous challenges within the host, including high levels of copper. We have previously shown that M. tuberculosis CsoR is a copper inducible transcriptional regulator. Here we examined the hypothesis that csoR is necessary for maintaining copper homeostasis and surviving under various stress conditions. With an unmarked csoR knockout strain, we were able to characterize the role of csoR in M. tuberculosis as it faced copper and host stress. Growth under high levels of copper demonstrated that M. tuberculosis survives copper stress significantly better in the absence of csoR. Yet under minimal levels of copper, differential expression analysis revealed that the loss of csoR results in a cell wide hypoxia-type stress response with the induction of the DosR regulon. Despite the stress placed on M. tuberculosis by the loss of csoR, survival of the knockout strain was increased compared to wild type during the early chronic stages of mouse infection, suggesting that csoR could play an active role in modulating M. tuberculosis fitness within the host. Overall, analysis of CsoR provided an increased understanding of the M. tuberculosis copper response with implications for other intracellular pathogens harboring CsoR.