Hydrogen peroxide activates the SoxRS regulon in vivo.

By multiplex reverse transcription-PCR, we demonstrate that the SoxRS response, which protects cells against superoxide toxicity, is triggered also by hydrogen peroxide. SoxR-dependent inductions of 7. 3-, 7.6-, 4.6-, 2.2-, and 2.6-fold were quantified for soxS, micF, sodA, inaA, and fpr transcripts, respectively. This finding suggests an extensive and tight connectivity between different regulatory pathways in the Escherichia coli response to oxidative stress.