Appropriate DevR (DosR)-Mediated Signaling Determines Transcriptional Response, Hypoxic Viability and Virulence of Mycobacterium tuberculosis

Background: The DevR(DosR) regulon is implicated in hypoxic adaptation and virulence of Mycobacterium tuberculosis. The present study was designed to decipher the impact of perturbation in DevR-mediated signaling on these properties. Methodology/Principal Findings: M. tb complemented (Comp) strains expressing different levels of DevR were constructed in Mut1* background (expressing DevR N-terminal domain in fusion with AphI (DevR(N)-Kan) and in Mut2 Delta devR background (deletion mutant). They were compared for their hypoxia adaptation and virulence properties. Diverse phenotypes were noted; basal level expression (similar to 5.3 +/- 2.3 mu M) when induced to levels equivalent to WT levels (similar to 25.8 +/- 9.3 mu M) was associated with robust DevR regulon induction and hypoxic adaptation (Comp 9* and 10*), whereas low-level expression (detectable at transcript level) as in Comp 11* and Comp15 was associated with an adaptation defect. Intermediate-level expression (similar to 3.3 +/- 1.2 mu M) partially restored hypoxic adaptation functions in Comp2, but not in Comp1* bacteria that co-expressed DevR(N)-Kan. Comp* strains in Mut1* background also exhibited diverse virulence phenotypes; high/very low-level DevR expression was associated with virulence whereas intermediate-level expression was associated with low virulence. Transcription profiling and gene expression analysis revealed up-regulation of the phosphate starvation response (PSR) in Mut1* and Comp11* bacteria, but not in WT/Mut2 Delta devR/other Comp strains, indicating a plasticity in expression pathways that is determined by the magnitude of signaling perturbation through DevR(N)-Kan. Conclusions/Significance: A minimum DevR concentration of similar to 3.3 +/- 1.2 mu M (as in Comp2 bacteria) is required to support HspX expression in the standing culture hypoxia model. The relative intracellular concentrations of DevR and DevR(N)-Kan appear to be critical for determining dormancy regulon induction, hypoxic adaptation and virulence. Dysregulated DevR(N)-Kan- mediated signaling selectively triggers the PSR in bacteria expressing no/very low level of DevR. Our findings illustrate the important role of appropriate two-component-mediated signaling in pathogen physiology and the resilience of bacteria when such signaling is perturbed.