Mechanism of H2S-mediated protection against oxidative stress inEscherichia coli

Abstract

Endogenous hydrogen sulfide (H2S) renders bacteria highly resistant to oxidative stress, but its mechanism remains poorly understood. Here, we report that 3-mercaptopyruvate sulfurtransferase (3MST) is the major source of endogenous H2S inEscherichia coli. Cellular resistance to H2O2strongly depends on the activity ofmstA, a gene that encodes 3MST. Deletion of the ferric uptake regulator (Fur) renders ∆mstAcells hypersensitive to H2O2. Conversely, induction of chromosomalmstAfrom a strong pLtetO-1 promoter (Ptet-mstA) renders ∆furcells fully resistant to H2O2. Furthermore, the endogenous level of H2S is reduced in ∆furor ∆sodA∆sodBcells but restored after the addition of an iron chelator dipyridyl. Using a highly sensitive reporter of the global response to DNA damage (SOS) and the TUNEL assay, we show that 3MST-derived H2S protects chromosomal DNA from oxidative damage. We also show that the induction of the CysB regulon in response to oxidative stress depends on 3MST, whereas the CysB-regulatedl-cystine transporter, TcyP, plays the principle role in the 3MST-mediated generation of H2S. These findings led us to propose a model to explain the interplay betweenl-cysteine metabolism, H2S production, and oxidative stress, in which 3MST protectsE. coliagainst oxidative stress vial-cysteine utilization and H2S-mediated sequestration of free iron necessary for the genotoxic Fenton reaction.