FIG. 3.
(A) Sensitivity of O. tritici strains to chromate. Cultures of O. tritici 5bvl1 (♦), O. triticiT (▪), O. triticiT chrFCAB (▴), O. triticiT chrCAB (×), O. triticiT chrAB (□), and O. triticiT chrB (○) strains were grown in Tris-glucose medium for 15 h at 37°C in the presence of the indicated concentrations of chromate. (B) Clonogenic survival at different chromate concentrations. The cultures were plated on LB plates, and the colonies were counted after 3 days of incubation at 37°C. Strain symbols are as defined above for panel A. (C) Chromate uptake by O. tritici strains. Exponential-phase cells were incubated at 37°C with chromate for 3 h, and cellular chromium concentrations were measured as described in Materials and Methods. (D) Survival of O. tritici 5bvl1 (♦), O. tritici (○), E117 mutant (▴), and E117:chrA (×) strains at different chromate concentrations. The cultures were also plated on LB plates, and the colonies were counted after 3 days of incubation at 37°C. (E) Chromate uptake. Exponential growing cells were exposed to 1 mM chromate for 3 h. Values are means ± standard deviations (error bars) from three independent experiments. (F) Chromate efflux by O. tritici 5bvl1 (○), E117 mutant (▪), and E117:chrA (▴) strains. Cells were first preincubated with 0.1 mM chromate for 1 h to induce the chr operon and then pulse-loaded for 15 min with high chromate concentrations (1 mM chromate for E117 mutant and 5 mM chromate for strains 5bvl1 and E117:chrA), resulting in approximately equal initial levels of cellular chromium. Cells were washed and then incubated in fresh medium for 0 to 30 min at 37°C to assess efflux of cellular chromium. Results are the percentages of remaining cellular concentrations of Cr after normalization for protein content (means ± standard deviations [error bars] from three independent experiments).