Alexander Mironov a , b , Tatyana Seregina b , Maxim Nagornykh b , Lyly G. Luhachack c , Natalya Korolkova a , Liubov Errais Lopes a , Vera Kotova a , Gennady Zavilgelsky a , Rustem Shakulov a , Konstantin Shatalin c , Evgeny Nudler c , d , 1
22 May 2017
Hydrogen sulfide (H 2S) is a highly toxic gas that interferes with cellular respiration; however, at low physiological amounts, it plays an important role in cell signaling. Remarkably, in bacteria, endogenously produced H 2S has been recently recognized as a general protective molecule, which renders multiple bacterial species highly resistant to oxidative stress and various classes of antibiotics. The mechanism of this phenomenon remains poorly understood. In this paper, we use Escherichia coli as a model system to elucidate its major enzymatic source of H 2S and establish the principle biochemical pathways that account for H 2S-mediated protection against reactive oxygen species. Understanding those mechanisms has far-reaching implications in preventing bacterial resistance and designing effective antimicrobial therapies.
Endogenous hydrogen sulfide (H 2S) 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 H 2S in Escherichia coli. Cellular resistance to H 2O 2 strongly depends on the activity of mstA, a gene that encodes 3MST. Deletion of the ferric uptake regulator (Fur) renders ∆ mstA cells hypersensitive to H 2O 2. Conversely, induction of chromosomal mstA from a strong pLtetO-1 promoter (P tet - mstA) renders ∆ fur cells fully resistant to H 2O 2. Furthermore, the endogenous level of H 2S 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 H 2S 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 H 2S. These findings led us to propose a model to explain the interplay between l-cysteine metabolism, H 2S production, and oxidative stress, in which 3MST protects E. coli against oxidative stress via l-cysteine utilization and H 2S-mediated sequestration of free iron necessary for the genotoxic Fenton reaction.