Figure 1. Kinetics of H₂O₂ degradation by actively growing C. neoformans cells and the effect of concentration of peroxide on fungal viability.

A: 1 mM H₂O₂ was added to KN99 cells growing in YNB, pH 4 at OD₆₅₀ = 1.5 (□), YNB medium alone ( ), spent media (Δ) and to heat killed C. neoformans cells (▪). Various concentrations of H₂O₂ were added to the cells growing either in YPD (B) or in YNB (C) medium. At various time points samples were withdrawn, cells were separated by centrifugation and the supernatant was used for the quantitative estimation of H₂O₂. Percentage of residual H₂O₂ was plotted against treatment time. Error bars reflect standard error calculated from three independent experiments. D: Exponentially growing cells at OD₆₅₀ = 1.5 were incubated with various concentrations of H₂O₂. At various time points aliquots were withdrawn, cells collected by centrifugation at 4°C, washed two times with cold PBS. Washed cells were serially diluted and plated on solid YPD media, then incubated at 30°C. After 3 days colony forming units (CFU) were counted. Fraction of viable cells was plotted against H₂O₂ treatment time.