(C) Iron sensitivity assay. Cells were grown overnight in PS medium and cultures were diluted in fresh media at an density of 1 x 106 cells/ml, treated in the absence or presence of 500 µM FeSO4. Viability of cultures was measured at the indicated time point by dilution plating. Percent survival was determined as the number of viable cells at each time divided by the number of viable cells before exposure to FeSO4. Data shown are mean ± SE (n=3). * indicates p-value < 0.05 and ** indicates p-value < 0.01 compared with data obtained from iron treated wild type and mutant by paired student t-test. 