AUTHOR=Wang Jun , Guo Xin , Li Heng , Qi Haizhen , Qian Jing , Yan Shasha , Shi Junling , Niu Weining 

TITLE=Hydrogen Sulfide From Cysteine Desulfurase, Not 3-Mercaptopyruvate Sulfurtransferase, Contributes to Sustaining Cell Growth and Bioenergetics in E. coli Under Anaerobic Conditions

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.02357

DOI=10.3389/fmicb.2019.02357

ISSN=1664-302X

ABSTRACT=<p>Endogenous hydrogen sulfide (H<sub>2</sub>S), which is primarily generated by 3-mercaptopyruvate sulfurtransferase (3-MST) in <italic>Escherichia coli</italic> (<italic>E. coli</italic>) 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 H<sub>2</sub>S in <italic>E. coli</italic> under anaerobic conditions. A significant decrease in H<sub>2</sub>S production under anaerobic conditions was observed in <italic>E. coli</italic> upon deletion of IscS, but not in 3-MST-deficient bacteria (Δ<italic>mstA</italic>). Furthermore, the H<sub>2</sub>S-producing activity of recombinant IscS using <italic>L</italic>-cysteine as a substrate exhibited an approximately 2.6-fold increase in the presence of dithiothreitol (DTT), indicating that H<sub>2</sub>S 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 <italic>E. coli</italic> cells H<sub>2</sub>S production from IscS is regulated under oxidative and reductive stress. A mutant <italic>E. coli</italic> (Δ<italic>iscS</italic>) strain lacking a chromosomal copy of the IscS-encoding gene <italic>iscS</italic> 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 Na<sub>2</sub>S (an H<sub>2</sub>S 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 Na<sub>2</sub>S to culture medium stimulates ATP synthesis in the mutant <italic>E. coli</italic> (Δ<italic>iscS</italic>) strain in the logarithmic growth phase but suppresses ATP synthesis in wild-type <italic>E. coli</italic>. Our results reveal a new H<sub>2</sub>S-producing pathway in <italic>E. coli</italic> under anaerobic conditions and show that hydrogen sulfide from IscS contributes to sustaining cell growth and bioenergetics under oxygen-deficient conditions.</p>