As inhabitants of soda lakes, Thioalkalivibrio versutus are halo- and alkaliphilic bacteria that have previously been shown to respire with the first demonstrated Na+-translocating cytochrome-c oxidase (CO). The enzyme generates a sodium-motive force (Ds) as high as -270 mV across the bacterial plasma membrane. However, in these bacteria, operation of the possible Ds consumers has not been proven. We obtained motile cells and used them to study the supposed Na+ energeticcycle in these bacteria. The resulting motility was activated in the presence of the protonophore2-heptyl-4-hydroxyquinoline N-oxide (HQNO), in line with the same effect on cell respiration, andwas fully blocked by amiloride—an inhibitor of Na+-motive flagella. In immotile starving bacteria, ascorbate triggered CO-mediated respiration and motility, both showing the same dependence on sodium concentration. We concluded that, in T. versutus, Na+-translocating CO and Na+-motive flagella operate in the Na+ energetic cycle mode. Our research may shed light on the energetic reasonfor how these bacteria are confined to a narrow chemocline zone and thrive in the extreme conditions of soda lakes.@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

Stable development of a heterotrophic bacterial satellite with a peculiar cell morphology has been observed in several enrichment cultures of haloalkaliphilic benthic filamentous cyanobacteria from a hypersaline soda lake in Kulunda Steppe (Altai, Russia). The organism was isolated in pure culture (strain Omega) using sonicated cyanobacterial cells as substrate and it was identified as a deep phylogenetic lineage within the recently proposed phylum Balneolaeota. It is an obligately aerobic heterotroph utilizing proteins and peptides for growth. The cell morphology significantly varied from semicircles to long filaments depending on the growth conditions. The cultures are red-orange colored due to a presence of carotenoids. The isolate is an obligate alkaliphile with a pH range for growth from 8.5 to 10.5 (optimum at 9.5-10) and moderately salt-tolerant with a range from 0.3 to 3 M total Na⁺ (optimum at 1 M). The genome analysis of strain Omega demonstrated a presence of gene, encoding a proteorhodopsin forming a separate branch in the sodium-translocating proteorhodopsin family. Experiments with washed cells of Omega confirmed light-dependent sodium export. A possible physiological role of the sodium proteorhodopsin in strain Omega is discussed. Phylogenomic analysis demostrated that strain Omega forms an deep, independent branch of a new genus and family level within a recently established phylum Balneolaeota.

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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

A chemolithoautotrophic sulfur-oxidizing bacterium (SOB) strain ALCO 1 capable of growing at both near-neutral and extremely alkaline pH was isolated from hypersaline soda lakes in S-W Siberia (Altai, Russia). Strain ALCO 1 represents a novel separate branch within the halothiobacilli in the Gammaproteobacteria, which, so far, contained only neutro-halophilic SOB. On the basis of its unique phenotypic properties and distant phylogeny, strain ALCO 1 is proposed as a new genus and species Thioalkalibacter halophilus gen. nov. sp. nov. ALCO 1 was able to grow within a broad range of salinity (0.5-3.5 M of total sodium) with an optimum at around 1 M Na+, and pH (7.2-10.2, pHopt at around 8.5). Na+ was required for sulfur-dependent respiration in ALCO 1. The neutral (NaCl)-grown chemostat culture had a much lower maximum growth rate (μmax), respiratory activity and total cytochrome c content than its alkaline-grown counterpart. The specific concentration of osmolytes (ectoine and glycine-betaine) produced at neutral pH and 3 M NaCl was roughly two times higher than at pH 10 in soda. Altogether, strain ALCO 1 represents an interesting chemolithoautotrophic model organism for comparative investigations of bacterial adaptations to high salinity and pH.@en