Attenuation of virulence in Mycobacterium tuberculosis expressing a constitutively active iron repressor

Proc Natl Acad Sci U S A. 1999 Oct 26;96(22):12844-8. doi: 10.1073/pnas.96.22.12844.


Iron is an essential nutrient for the survival of most organisms and has played a central role in the virulence of many infectious disease pathogens. Mycobacterial IdeR is an iron-dependent repressor that shows 80% identity in the functional domains with its corynebacterial homologue, DtxR (diphtheria toxin repressor). We have transformed Mycobacterium tuberculosis with a vector expressing an iron-independent, positive dominant, corynebacterial dtxR hyperrepressor, DtxR(E175K). Western blots of whole-cell lysates of M. tuberculosis expressing the dtxR(E175K) gene revealed the stable expression of the mutant protein in mycobacteria. BALB/c mice were infected by tail vein injection with 2 x 10(5) organisms of wild type or M. tuberculosis transformed with the dtxR mutant. At 16 weeks, there was a 1.2 log reduction in bacterial survivors in both spleen (P = 0.0002) and lungs (P = 0.006) with M. tuberculosis DtxR(E175K). A phenotypic difference in colonial morphology between the two strains also was noted. A computerized search of the M. tuberculosis genome for the palindromic consensus sequence to which DtxR and IdeR bind revealed six putative "iron boxes" within 200 bp of an ORF. Using a gel-shift assay we showed that purified DtxR binds to the operator region of five of these boxes. Attenuation of M. tuberculosis can be achieved by the insertion of a plasmid containing a constitutively active, iron-insensitive repressor, DtxR(E175K), which is a homologue of IdeR. Our results strongly suggest that IdeR controls genes essential for virulence in M. tuberculosis.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Bacterial Proteins / genetics*
  • Base Sequence
  • Cloning, Molecular
  • Corynebacterium / genetics
  • DNA, Bacterial
  • DNA-Binding Proteins / genetics*
  • Iron / metabolism*
  • Mice
  • Mice, Inbred BALB C
  • Molecular Sequence Data
  • Mycobacterium tuberculosis / genetics
  • Mycobacterium tuberculosis / pathogenicity*
  • Repressor Proteins / genetics*
  • Sequence Homology, Nucleic Acid
  • Virulence / genetics*


  • Bacterial Proteins
  • DNA, Bacterial
  • DNA-Binding Proteins
  • DtxR protein, Corynebacterium diphtheriae
  • Repressor Proteins
  • Iron