FIG 4 .

Inability to export zinc increases copper stress. (A) Endpoint growth of wild-type S. pneumoniae TIGR4 and ΔcopA, ΔczcD, and ΔcopA ΔczcD mutants in the presence of various concentrations of Zn²⁺ after 18 h of growth in THYB at pH 6.5 at 37°C. Error bars represent standard deviations and are representative of at least three independent experiments. *, P < 0.01 in a Student t test. (B) Timed growth curve of wild-type (WT) TIGR4 and the ΔczcD mutant under various concentrations of copper stress in THYB at pH 6.5 at 37°C. #, P < 0.01 in a paired t test. (C) Endpoint growth of wild-type S. pneumoniae TIGR4 and the ΔczcD mutant in a nonlethal concentration of Zn²⁺ (75 µM) and approximately the 50% lethal dose of Cu²⁺ (500 µM) after 18 h of growth in THYB at pH 6.5 at 37°C. *, P < 0.02 in a Student t test. ns, no significant difference.