Mycobacterium tuberculosis Requires Phosphate-Responsive Gene Regulation to Resist Host Immunity

Mycobacterium tuberculosis persists in the lungs of mammalian hosts despite inducing an immune response dominated by the macrophage-activating cytokine interferon-gamma (IFN-gamma). We identified the M. tuberculosis phosphate uptake system component PstA1 as a factor required to resist IFN-gamma dependent immunity. A ∆pstA1 mutant was fully virulent in IFN-gamma-/- mice but was attenuated in mice lacking the IFN-gamma-inducible nitric oxide synthase (NOS2). This phenotype suggests that ∆pstA1 bacteria are hypersensitive to an IFN-gamma-dependent immune mechanism(s) other than NOS2. In other species, the Pst system participates in phosphate-responsive gene regulation by interacting with a two-component signal transduction system. We identified genes that exhibited dysregulated expression in the ∆pstA1 mutant and showed that aberrant gene expression was dependent on the two-component system response regulator RegX3. Deletion of regX3 suppressed the replication and virulence defects of ∆pstA1 bacteria in NOS2-/- mice, suggesting that the ∆pstA1 mutant is attenuated, in part, due to aberrant RegX3-dependent gene expression. Our data imply that phosphate is an important signal controlling M. tuberculosis gene expression during replication in the lung. Aerobically growing logarithmic phase Wt or pstA1/regX3/pstA1regX3 mutant strains were grown in phosphate replete media and analyzed after several hours. Experiments were repeated in triplicate (pstA1 mutant) or quadruplicate (regX3/pstA1regX3 mutant).