Inhibiting the stringent response blocks Mycobacterium tuberculosis entry into quiescence and reduces persistence

The stringent response enables Mycobacterium tuberculosis (Mtb) to shut down its replication and metabolism under various stresses. Here we show that Mtb lacking the stringent response enzyme Rel(Mtb) was unable to slow its replication rate during nutrient starvation. Metabolomics analysis revealed that the nutrient-starved rel(Mtb)-deficient strain had increased metabolism similar to that of exponentially growing wild-type bacteria in nutrient-rich broth, consistent with an inability to enter quiescence. Deficiency of rel(Mtb) increased the susceptibility of mutant bacteria to killing by isoniazid during nutrient starvation and in the lungs of chronically infected mice. We screened a pharmaceutical library of over 2 million compounds for inhibitors of Rel(Mtb) and showed that the lead compound X9 was able to directly kill nutrient-starved M. tuberculosis and enhanced the killing activity of isoniazid. Inhibition of Rel(Mtb) is a promising approach to target M. tuberculosis persisters, with the potential to shorten the duration of TB treatment.