Effect of Spx on PQ induced expression of msrA. A. RT-PCR analysis of the expression of msrA in wild-type strain (168) and spx mutant (BSY5000). 100% expression for each strain is defined as the expression of msrA without any oxidants treatment. Strains 168 and BSY5000 were grown in ED minimal medium to mid-exponential phase and incubated with or without PQ (100 μM) for 15 min. B. Disc inhibition assay of PQ induced oxidative stress for wild-type 168 strain and spx disrupted strain (BSY5000). C. msrA expression in a clpX mutant strain. RT-PCR analysis of the expression of msrA in wild-type 168 strain, clpX mutant (BSY6000) and clpX, spx double mutant (BSY4260). 100% expression is defined as the expression of msrA in wild-type strain 168. Strains were grown in LB rich medium to mid-exponential phase.