Figure 3.

PNPase-deficient cells are hypersensitive to H₂O₂ and PMS. (A) Sensitivity of wild-type (WT) and pnp mutant cells to H₂O₂. Cultures were grown, diluted, and inoculated as described in Figure 2A. (B) Sensitivity of wild-type and pnp mutant cells to phenazine methosulfate (PMS). (C) Sensitivity of wild-type and pnp mutant cells to H₂O₂ determined by cell density. Cultures were grown to exponential phase in liquid YT medium, treated with indicated concentrations of H₂O₂ for 90 min in a 96-well plate (n = 4), and incubated at 37 °C with shaking at 150 rpm. Cell density was measured in a plate reader at OD_550nm and is expressed as the percent of an untreated control. (D) Sensitivity to H₂O₂ determined by colony forming units (cfu). Exponentially growing cultures were challenged with the indicated concentrations of H₂O₂ for 90 min. The cultures were then diluted, plated on YT agar plates, and incubated overnight at 37 °C. The data are expressed as the percent of an untreated control.