Two-component systems play a central role in the adaptation of pathogenic bacteria to the environment prevailing within host tissues. The genes encoding the response regulator DevR (Rv3133c/DosR) and the cytoplasmic portion (DevS 201 ) of the histidine kinase DevS (Rv3132c/DosS), a putative two-component system of Mycobacterium tuberculosis, were cloned and the protein products were overexpressed, purified and refolded as N-terminally His 6 -tagged proteins from Escherichia coli.

The devR-devS two-component system of Mycobacterium tuberculosis was identified earlier and partially characterized in our laboratory. A devR: :kan mutant of M. tuberculosis was constructed by allelic exchange. The devR mutant strain showed reduced cell-tocell adherence in comparison to the parental strain in laboratory culture media. This phenotype was reversed on complementation with a wild-type copy of devR. The devR mutant and parental strains grew at equivalent rates within human monocytes either in the absence or in the presence of lymphocytic cells. The expression of DevR was not modulated upon entry of M. tuberculosis into human monocytes. However, guinea pigs infected with the mutant strain showed a significant decrease in gross lesions in lung, liver and spleen ; only mild pathological changes in liver and lung; and a nearly 3 log lower bacterial burden in spleen compared to guinea pigs infected with the parental strain. Our results suggest that DevR is required for virulence in guinea pigs but is not essential for entry, survival and multiplication of M. tuberculosis within human monocytes in vitro. The attenuation in virulence of the devR mutant in guinea pigs together with DevR-DevS being a bona fide signal transduction system indicates that DevR plays a critical and regulatory role in the adaptation and survival of M. tuberculosis within tissues.

The Mycobacterium tuberculosis prrA-prrB (Rv0903c-Rv0902c) two-component regulatory system is expressed during intracellular growth in human macrophages and is required for early intracellular multiplication in murine macrophages, suggesting its importance in establishing infection. To better understand the function of the prrA-prrB two-component system, we defined the transcriptional characteristics of the prrA and prrB genes during exponential and stationary growth and upon exposure to different environmental stresses and attempted to generate a prrA-prrB deletion mutant. The prrA and prrB genes constitute an operon and are cotranscribed during logarithmic growth, with transcriptional levels decreasing in stationary phase and during hypoxia. Despite the transcriptional differences, PrrA protein levels remained relatively stable throughout growth and in hypoxia. Under conditions of nitrogen limitation, prrAB transcription was induced, while acidic pH stress and carbon starvation did not significantly alter transcript levels. Deletion of the prrAB operon on the chromosome of M. tuberculosis H37Rv occurred only in the presence of an episomal copy of the prrAB genes, indicating that this two-component system is essential for viability. Characterization of the prrAB locus in M. tuberculosis Mt21D3, a previously described prrA transposon mutant, revealed that this strain is not a true prrA knockout mutant. Rather, Tn5367 transposon insertion into the prrA promoter only decreased prrA and prrB transcription and PrrA levels in Mt21D3 compared to those in the parental Mt103 clinical strain. These data provide the first report describing the essentiality of the M. tuberculosis prrAB two-component system and reveal insights into its potential role in mycobacterial growth and metabolism.T uberculosis continues to be a global health emergency. According to 2009 WHO statistics, 9.4 million new cases of tuberculosis were diagnosed and 1.7 million people died from the disease (equivalent to 4,700 deaths each day) (29). This global emergency is further exacerbated by multidrug-resistant and extensively drug-resistant Mycobacterium tuberculosis strains that are resistant to our best antibiotics and thus difficult to treat (14). A hallmark in the life cycle of M. tuberculosis is its intracellular residence within the human macrophage. To ensure its intracellular survival, M. tuberculosis must adapt to the host environment by appropriately regulating the expression of genes involved in virulence and metabolism. Understanding how M. tuberculosis regulatory systems coordinate complex adaptations is critical to deciphering the ongoing interactions that govern establishment and progression of tuberculosis disease.Like most bacteria, M. tuberculosis uses two-component systems to execute transcriptional reprogramming in response to changing environments. Of the 11 paired two-component systems, two orphan histidine kinase genes, and six orphan response regulator genes (15), at least three M. tuberculosis response regulators (phoP, devR,...