Distinct and novel shared regulatory mechanisms influence Mtb response to abundant ions.

(A) rv0500A disruption enhances Mtb response to acidic pH and high [Cl-]. WT, rv0500A::Tn, or rv0500A* (complemented mutant) Mtb carrying the Cl-/pH responsive rv2390c’::GFP reporter were grown in pH 7 or pH 5.7 media, ± 250 mM NaCl, for 9 days. GFP signal in fixed samples was measured by FACS, with fold signal induction compared to the corresponding strain grown in pH 7 control media. Data are shown as means ± SD from 3–4 independent experiments. p-values were obtained with an unpaired t-test, * p+. WT or phoP::Tn Mtb carrying the K+-responsive kdpF’::GFP reporter were grown in standard 7H9 media (control) or K+-free 7H9. Samples were taken at indicated time points, fixed, and GFP induction analyzed by FACS. Data are shown as means ± SD from 3 independent experiments. (C) rv0500A disruption enhances Mtb response to low [K+]. WT, rv0500A::Tn, or rv0500A* Mtb carrying the kdpF’::GFP reporter were grown in standard 7H9 media or K+-free 7H9 for 9 days. GFP reporter induction was determined as in (A). Data are shown as means ± SD from 3–5 independent experiments. p-values were obtained with an unpaired t-test, ** p<0.01, *** p<0.001.