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REVIEW: Terminal Oxidase Cytochrome bd Protects Bacteria Against Hydrogen Sulfide Toxicity

Vitaliy B. Borisov1,a* and Elena Forte2

1Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119991 Moscow, Russia

2Department of Biochemical Sciences, Sapienza University of Rome, I-00185 Rome, Italy

* To whom correspondence should be addressed.

Received September 15, 2020; Revised September 15, 2020; Accepted October 26, 2020
Hydrogen sulfide (H2S) is often called the third gasotransmitter (after nitric oxide and carbon monoxide), or endogenous gaseous signaling molecule. This compound plays important roles in organisms from different taxonomic groups, from bacteria to animals and humans. In mammalian cells, H2S has a cytoprotective effect at nanomolar concentrations, but becomes cytotoxic at higher concentrations. The primary target of H2S is mitochondria. At submicromolar concentrations, H2S inhibits mitochondrial heme-copper cytochrome c oxidase, thereby blocking aerobic respiration and oxidative phosphorylation and eventually leading to cell death. Since the concentration of H2S in the gut is extremely high, the question arises – how can gut bacteria maintain the functioning of their oxygen-dependent respiratory electron transport chains under such conditions? This review provides an answer to this question and discusses the key role of non-canonical bd-type terminal oxidases of the enterobacterium Escherichia coli, a component of the gut microbiota, in maintaining aerobic respiration and growth in the presence of toxic concentrations of H2S in the light of recent experimental data.
KEY WORDS: respiratory chain, terminal oxidase, heme-copper oxidase, cytochrome bd, heme

DOI: 10.1134/S000629792101003X