Mycobacterium tuberculosis growth arrest on propionate at acidic pH is suppressed by mutations in phoPR and pyrazinamide treatment

Mycobacterium tuberculosis (Mtb) arrests its growth at acidic pH, when grown on specific single carbon sources, including propionate. To understand the basis of the propionate-driven growth arrest at acidic pH, we conducted a genetic selection for mutants enabling growth on propionate at pH 5.7. All the selected mutants had insertions in the two-component regulatory genes phoR or phoP . We hypothesized that growth arrest at acidic pH is caused by PhoPR diverting carbon from central carbon metabolism towards lipid anabolism and that when PhoPR is inactivated, growth is promoted through metabolizing propionate by the methyl citrate cycle (MCC) into pyruvate, a permissive carbon source for growth at acidic pH. Using chemical inhibition and mutants of the MCC pathway, we demonstrate that the enhanced growth is dependent on the MCC. Furthermore, stimulating lipid synthesis via the methylmalonyl-CoA pathway by adding vitamin B12 restricts growth in the phoPR mutant and, conversely, restricting lipid anabolism by inhibiting the triacylglycerol (TAG) synthase Tgs1 enhances growth of the phoPR mutant. Notably, CoA pools increased in the phoPR mutant grown on propionate, directly supporting our model. Given the role of CoA metabolism in pyrazinamide sensitivity, Mtb sensitivity to pyrazinamide was examined on propionate at acidic pH. Surprisingly, pyrazinamide treatment of WT Mtb suppresses growth arrest on propionate at acidic pH. In contrast, the phoPR mutant has enhanced sensitivity to pyrazinamide. Together, these findings support that propionate-driven growth arrest at acidic pH is caused by metabolic remodeling that is regulated by PhoPR and is associated with pyrazinamide sensitivity.