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Abstract
Endogenous hydrogen sulfide (H2S), which is primarily generated by 3-mercaptopyruvate sulfurtransferase (3-MST) in Escherichia coli (E. coli) under aerobic conditions, renders bacteria highly resistant to oxidative stress. However, the biosynthetic pathway and physiological role of this gas under anaerobic conditions remains largely unknown. In the present study, we demonstrate that cysteine desulfurase (IscS), not 3-MST, is the primary source of endogenous H2S in E. coli under anaerobic conditions. A significant decrease in H2S production under anaerobic conditions was observed in E. coli upon deletion of IscS, but not in 3-MST-deficient bacteria (ΔmstA). Furthermore, the H2S-producing activity of recombinant IscS using L-cysteine as a substrate exhibited an approximately 2.6-fold increase in the presence of dithiothreitol (DTT), indicating that H2S production catalyzed by IscS was greatly increased under reducing conditions. The activity of IscS was regulated under the different redox conditions and the midpoint redox potential was determined to be −329 ± 1.6 mV. Moreover, in E. coli cells H2S production from IscS is regulated under oxidative and reductive stress. A mutant E. coli (ΔiscS) strain lacking a chromosomal copy of the IscS-encoding gene iscS showed significant growth defects and low levels of ATP under both aerobic and anaerobic conditions. The growth defects could be fully restored after addition of 500 μM Na2S (an H2S donor) under anaerobic conditions, but not by the addition of cysteine, sodium sulfite or sodium sulfate. We also showed that the addition of 500 μM Na2S to culture medium stimulates ATP synthesis in the mutant E. coli (ΔiscS) strain in the logarithmic growth phase but suppresses ATP synthesis in wild-type E. coli. Our results reveal a new H2S-producing pathway in E. coli under anaerobic conditions and show that hydrogen sulfide from IscS contributes to sustaining cell growth and bioenergetics under oxygen-deficient conditions.
Highlights
The noxious gas hydrogen sulfide (H2S) is recognized as a third gas signaling molecule together with nitric oxide (NO) and carbon monoxide (CO), which play important roles in mammals, including in inflammation, vascular tone, angiogenesis, cancer, and protection against oxidative stress (Chen et al, 2012; Kimura, 2014; Niu et al, 2018a)
In Escherichia coli (E. coli) grown in Luria-Bertani (LB) broth, H2S is primarily generated by 3-MST under aerobic culture conditions and can defend against oxidative stress induced by antibiotics (Shatalin et al, 2011; Mironov et al, 2017)
We report that endogenous H2S production in E. coli under anaerobic conditions was primarily generated from cysteine desulfurase but not 3-mercaptopyruvate sulfurtransferase
Summary
The noxious gas hydrogen sulfide (H2S) is recognized as a third gas signaling molecule together with nitric oxide (NO) and carbon monoxide (CO), which play important roles in mammals, including in inflammation, vascular tone, angiogenesis, cancer, and protection against oxidative stress (Chen et al, 2012; Kimura, 2014; Niu et al, 2018a). Cysteine desulfurase is one of the key enzymes involved in H2S biogenesis (Scuffi et al, 2014) Based on these results, we hypothesize that cysteine desulfurase in E. coli is probably involved in the synthesis of H2S under anaerobic conditions and that endogenous H2S production may sustain cellular bioenergetics under oxygen-deficient conditions. We report that endogenous H2S production in E. coli under anaerobic conditions was primarily generated from cysteine desulfurase but not 3-mercaptopyruvate sulfurtransferase. The addition of exogenous Na2S (an H2S donor), but not cysteine, sodium sulfite or sodium sulfate can stimulate ATP synthesis in the mutant E. coli ( iscS) strain under anaerobic conditions, indicating that H2S from cysteine desulfurase in E. coli contributes to sustaining cell growth and bioenergetics
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