FIG 4 .

ZntA and ZitB are the primary zinc efflux transporters in S. Typhimurium. (A) A ΔzntA mutant (pink) was impaired for growth, represented by a delayed exit from lag phase, in both 0.125 mM ZnSO₄ and 0.25 mM ZnSO₄, while a ΔzntB mutant (aqua) and a ΔzitB mutant (light green) exhibited growth comparable to wild type (blue) under these conditions. (B) Significance of the growth defect for the ΔzntA mutant in panel A was determined by calculating the mean time required to reach 50% of the maximum final OD₆₀₀ for each strain. (C) A ΔzntB ΔzitB double mutant (purple) exhibited growth comparable to wild type (blue) when exposed to elevated zinc concentrations. A ΔzntA ΔzntB mutant (red) behaved similarly to a ΔzntA mutant, whereas a ΔzntA ΔzitB mutant (green) displayed a more severe growth delay at 0.125 mM ZnSO₄ and was unable to grow at 0.25 mM ZnSO₄. A ΔzntA ΔzntB ΔzitB triple mutant (orange) exhibited growth characteristics identical to those of a ΔzntA ΔzitB double mutant. (D) Significance of the growth defects for the mutants in panel C was determined by calculating the mean time required to reach 50% of the maximum final OD₆₀₀ for each strain. Statistical significance of the growth defects was determined by unpaired two-tailed t test, and an asterisk indicates P values of <0.001 for ΔzntA, ΔzntA ΔzntB, ΔzntA ΔzitB, and ΔzntA ΔzntB ΔzitB mutants compared to wild type at all concentrations. Error bars represent standard deviations.