TERMINAL OXIDASE CYTOCHROME <i>bd</i> PROTECTS BACTERIA AGAINST HYDROGEN SULFIDE TOXICITY
Hydrogen sulfide (H<sub>2</sub>S) 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, H<sub>2</sub>S has a cytoprotective effect at nanomolar concentrations, but becomes cytotoxic at higher concentrations. The primary target of H<sub>2</sub>S is mitochondria. At submicromolar concentrations, H<sub>2</sub>S inhibits mitochondrial heme-copper cytochrome <i>c</i> oxidase, thereby blocking aerobic respiration and oxidative phosphorylation and eventually leading to cell death. Since the concentration of H<sub>2</sub>S 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 <i>bd</i>-type terminal oxidases of the enterobacterium <i>Escherichia coli</i>, a component of the gut microbiota, in maintaining aerobic respiration and growth in the presence of toxic concentrations of H<sub>2</sub>S in the light of recent experimental data.