FIG 4 .

Unregulated heme synthesis alters iron homeostasis. (A) Growth was measured in minimal medium containing vehicle or 1 µM iron chelator EDDHA. Graphed is the final growth as measured by the OD₆₀₀ for each S. aureus strain in medium containing EDDHA relative to vehicle. The data are the average of the means from five independent experiments each in at least biological triplicate with standard error of the mean shown. Statistical significance was determined using a one-way ANOVA with Dunnett’s correction for multiple comparisons, comparing the ΔhemX::P_lgt strain to each other strain. *, P < 0.05. (B) The activity of the iron limitation-responsive promoter P_isdA was measured by recording fluorescence intensity over time in rich medium containing vehicle or the iron chelator 2,2-dipyridyl. The data are the average of the means from three independent experiments each in biological triplicate with standard error of the mean shown. Statistical significance was determined using a one-way ANOVA with Sidak’s correction for multiple comparisons, comparing data for the WT and ΔhemX mutant under each condition. **, P < 0.01; ns, not significant.