FIG 1.

PDF overexpression restores growth in the presence of excess zinc. (A) A ΔzntA ΔzitB efflux-deficient mutant S. Typhimurium strain exhibits dose-dependent inhibition of exit from lag phase in the presence of supplemental ZnSO₄. The overexpression of PDF from an inducible plasmid (pdef) restores bacterial growth in the presence of zinc, in contrast to a vector control (pTrc99A). (B) The mean times required to reach the 50% maximum final OD₆₀₀ in panel A were compared at different ZnSO₄ concentrations in the absence or presence of PDF overexpression. (C) Overexpression of a PDF-C90S mutant (pdef-C90S) fails to restore the growth of the ΔzntA ΔzitB strain in the presence of ZnSO₄, while overexpression of a PDF-C130S mutant (pdef-C130S) partially relieves zinc inhibition. Significance was determined by an unpaired two-tailed t test relative to the vector control. **, P ≤ 0.01; ***, P ≤ 0.001; ****, P ≤ 0.0001; ns, nonsignificant (n = 3 to 6). Data are represented as means, with error bars showing standard deviations.