title: Appropriate DevR (DosR)-mediated signaling determines transcriptional response, hypoxic viability and virulence of Mycobacterium tuberculosis.
abstract: 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.
  
  
  RESULTS
  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 Mut2ΔdevR background (deletion mutant). They were compared for their hypoxia adaptation and virulence properties. Diverse phenotypes were noted; basal level expression (∼5.3±2.3 µM) when induced to levels equivalent to WT levels (∼25.8±9.3 µM) 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 (∼3.3±1.2 µM) 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/Mut2ΔdevR/other Comp strains, indicating a plasticity in expression pathways that is determined by the magnitude of signaling perturbation through DevR(N)-Kan.
  
  
  CONCLUSIONS
  A minimum DevR concentration of ∼3.3±1.2 µM (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.
authors.affiliation: Department of Biotechnology, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Shyamasree De
authors.initials: SD
authors.lastname: Majumdar
authors.forename: Atul
authors.initials: A
authors.lastname: Vashist
authors.forename: Sakshi
authors.initials: S
authors.lastname: Dhingra
authors.forename: Rajesh
authors.initials: R
authors.lastname: Gupta
authors.forename: Alka
authors.initials: A
authors.lastname: Singh
authors.forename: Vijay K
authors.initials: VK
authors.lastname: Challu
authors.forename: V D
authors.initials: VD
authors.lastname: Ramanathan
authors.forename: Prahlad
authors.initials: P
authors.lastname: Kumar
authors.forename: Jaya Sivaswami
authors.initials: JS
authors.lastname: Tyagi
mesh_terms: D000693:Anaerobiosis; D000818:Animals; D000942:Antigens, Bacterial / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins; D015964:Gene Expression Regulation, Bacterial; D006168:Guinea Pigs; D009169:Mycobacterium tuberculosis / Q000378:metabolism / Q000472:pathogenicity*; D010641:Phenotype; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014158:Transcription, Genetic; D014774:Virulence
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C542863:DosR protein, Mycobacterium tuberculosis; C118127:HspX protein, Mycobacterium tuberculosis; D011494:Protein Kinases