Mechanism of H 2 S-mediated protection against oxidative stress in Escherichia coli .

Endogenous hydrogen sulfide (H2 S) 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 H2 S in Escherichia coli Cellular resistance to H2 O2 strongly depends on the activity of mstA , a gene that encodes 3MST. Deletion of the ferric uptake regulator (Fur) renders ∆ mstA cells hypersensitive to H2 O2 Conversely, induction of chromosomal mstA from a strong pLtetO-1 promoter (P tet - mstA ) renders ∆ fur cells fully resistant to H2 O2 Furthermore, the endogenous level of H2 S is reduced in ∆ fur or ∆ sodA ∆ sodB cells 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 H2 S 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-regulated l-cystine transporter, TcyP, plays the principle role in the 3MST-mediated generation of H2 S. These findings led us to propose a model to explain the interplay between l-cysteine metabolism, H2 S production, and oxidative stress, in which 3MST protects E. coli against oxidative stress via l-cysteine utilization and H2 S-mediated sequestration of free iron necessary for the genotoxic Fenton reaction.