Cytochrome c oxidases (Coxs) are the basic energy transducers in the respiratory chain of the majority of aerobic organisms. Coxs studied to date are redox-driven proton-pumping enzymes belonging to one of three subfamilies: A-, B-, and C-type oxidases. The C-type oxidases (cbb3 cytochromes), which are widespread among pathogenic bacteria, are the least understood. In particular, the proton-pumping machinery of these Coxs has not yet been elucidated despite the availability of X-ray structure information. Here, we report the discovery of the first (to our knowledge) sodium-pumping Cox (Scox), a cbb3 cytochrome from the extremely alkaliphilic bacterium Thioalkalivibrio versutus. This finding offers clues to the previously unknown structure of the ionpumping channel in the C-type Coxs and provides insight into the functional properties of this enzyme.@en

The research aims at finding out the distinctive lines of energetics in natronophilic microorganisms started to be described (Banciu & Muntyan, 2015). Among used methods were analyses of respiratory characteristics, electrical potential generation, pH changes in cells/vesicles suspension upon light/oxygen impulses, effects of ionophores and uncouplers, visualization of sodium transport using radioisotope 22Na, phylogenetics. Summary of results: So far, a novel type of primary energy transformer, Na+‐motive cytochrome oxidase, which has been proven to operate in natronophilic strains of the genus Thioalkalivibrio (Muntyan et al., 2015), has been discovered, and then found in several other extremophiles. It has been demonstrated that in these same strains, cell motility is provided by Na+‐motive flagella. In addition, it was shown that the rhodopsin‐like pigment, proteorhodopsin, in the new natronophilic strain of a novel deep‐lineage of the phylum Balneolaeota, Cyclonatronum proteinivorum, pumps Na+ from cells (Sorokin et al., 2018). The screening of Na+‐motive energy mechanisms revealed the sodium energy cycle, consisting of (i) primary mechanisms for generating Na+‐potential and (ii) Na+‐potential consumers, represented by flagella and FoF1‐ATPase. Conclusion: Along the way, we first discovered that several species of bacteria simultaneously have in their genomes: (i) oxygen‐consuming generators of Na+‐potential (Na+‐pumping cbb3 oxidases) and (ii) consumers of Na+‐ potential such as Na+‐ATPase of F0F1‐type and flagella. Thus, for the first time, it became possible to establish the presence of a complete Na+‐cycle in energetics of oxygen‐respiring bacteria.@en