FIG.4.

Oxidative stress responses of rodA and pbp2b mutants. (A) Survival rates in the presence of increasing concentrations of menadione (Mnd). Symbols: ▵, control; ○, 6G4; , 18C3; and • (marked with an asterisk), rodA-pbp2. The control experiments were done with the strain 2C3, which was derived from CNRZ368 by pGh9:ISS1 transposition and which was neither affected in its oxidative stress response nor in its cell morphology. Cells were grown overnight in milk medium diluted 100-fold into fresh TPPY medium. At an OD₆₀₀ of 0.6, the culture was split and samples were treated with menadione for 3 h. Cells were then plated on TPPY liquid medium and incubated for 20 h in jars. The percentage of surviving cells was determined by comparing the number of CFU in treated samples with the number in untreated samples. All experiments were performed in triplicate. The results of typical experiments are presented here. (B) Growth inhibition of various mutants on TPPY medium in the presence of H₂O₂ and methyl viologen. The concentrations of the oxidative agents used in this experiment were 1 mM for H₂O₂ and 20 mM for methyl viologen (paraquat). The inhibition of growth was measured by determining the ratio of the OD₆₀₀ after a 20-h incubation in the presence of oxidizing agent to the OD₆₀₀ in the absence of treatment. All experiments were performed in triplicate. The data from typical experiments are displayed here.