Intensive microbiology studies of the past several decades of soda lakes, uncovered a rich functional diversity of haloalkaliphilic microbes driving carbon, nitrogen and sulfur cycles in these unique double-extreme habitats. One of the unexpected finding was a discovery there of aerobic extremely halophilic cellulotrophic natronoarchaea. Yet, little is still known about the identity of the soda lake bacteria able to use native cellulose as growth substrate, except for a single case of an anaerobic clostridium. In this work we present results of phenotypic and functional genomic analysis of an anaerobic bacterium, strain ANBcel5^T, enriched from hypersaline Siberian soda lakes with amorphous cellulose as growth substrate. Phylogenetic analysis placed the isolate into the family Chitinispirillaceae in the phylum Fibrobacterota as a new genus and species lineage with the 16S rRNA gene identity and Relative Evolutionary Divergence (RED) to its only known species Chitinispirillum alkaliphilum ACht6–1^T of 95.2 % and 0.847, respectively. In contrast, despite obvious morphological resemblance to ACht6–1^T, strain ANBcel5^T is a narrow cellulose-utilizing fermentative anaerobe fermenting cellulose and cellobiose to acetate, H₂ and succinate. It is a moderately salt-tolerant obligate alkaliphile growing optimally at 0.6 M total Na⁺ as carbonates and pH 9.5. Functional genome analysis of the isolate revealed the presence of multiple genes encoding extracellular endocellulases from the GH families 5 and 9, three sodium-translocating membrane complexes and osmolytes Nε-acetyl-β-lysine and glycine betaine biosynthesis. The bacterium is proposed to be classified as Cellulosispirillum alkaliphilum gen. nov., sp. nov. (DSM 113825 = UQM 41584).

Elemental sulfur disproportionation combined with obligate autotrophy is a unique type of sulfur-based anaerobic metabolism known in a limited number of bacteria, primarily found among the members of Desulfobacterota phylum. Until recently, the only characterized alkaliphilic representative of this group was Desulfurivibrio alkaliphilus, originally isolated as an H2-dependent sulfur reducer. In this study, we describe the properties of a novel species within this genus, Desulfurivibrio dismutans strain AMeS2, which was originally enriched and isolated from a soda lake sample as an autotrophic elemental sulfur disproportionating bacterium. Similar to D. alkaliphilus AHT 2T, D. dismutans AMeS2 is an obligately alkaliphilic and moderately salt-tolerant autotrophic bacterium. In contrast to known neutrophilic sulfur disproportionating bacteria, it is capable of disproportionating sulfur without Fe(III). It can also grow by dissimilatory sulfur reduction to sulfide or nitrate reduction to ammonium (DNRA) with formate (but not with H2) as the electron donor. The addition of formate to sulfur-disproportionating AMeS2 culture significantly increased the sulfur-reducing activity but did not completely abolish the oxidative branch of sulfur disproportionation. Genome analysis confirmed the presence of dissimilatory sulfur oxidation and dissimilatory sulfur and nitrate reduction machineries in the strain. S0 disproportionation occurs by means of cytoplasmic dissimilatory sulfite reductase (Dsr) donating electrons to, and periplasmic polysulfide reductase (PsrABC) receiving electrons from the menaquinone pool. Nitrate reduction to ammonium (DNRA) occurs by the combined action of a membrane formate dehydrogenase FdnGHI, periplasmic nitrate reductase, and octaheme c ammonifying nitrite reductase. Autotrophic growth is enabled by the Wood–Ljungdahl pathway (WLP). The genome also encodes proteins that presumably connect the oxidative branch of sulfur disproportionation with the carbon (WLP) cycle. Comparative proteomics of cells grown by sulfur disproportionation and formate-dependent DNRA demonstrated overexpression of the genes encoding Psr and rDSR at sulfur-disproportionating conditions, confirming their key role in this process. On the contrary, the genes encoding DNRA proteins are upregulated in the presence of nitrate. Thus, genomic and proteomic analyses revealed the pathways for energy conservation in a new representative of Desulfurivibrio growing at DNRA and under the thermodynamically challenging conditions of sulfur disproportionation.

Despite intensive microbiological characterization of soda lake microbial communities, no culturable representatives from the phylum Planctomycetota have been isolated from these haloalkaline habitats. In the context of studying polysaccharide utilization by soda lake microbial communities, we used polysaccharide hyaluronic acid as enrichment substrate at aerobic, moderate haloalkaline conditions (1 M total Na+, pH 9.5). This resulted in a
selective enrichment and isolation in pure culture of a bacterial strain AB-hyl4 belonging to Planctomycetota. The cells are tiny motile cocci growing in large aggregates, with the Gram-negative type of ultrastructure and producing a yellow pigment. This obligate aerobic saccharolytic heterotroph has an extremely narrow growth substrate range including, besides hyaluronic acid, melezitose and glycerol. The membrane lipids consist of phosphatidylcholine and two types of neutral lipids, including hopanoids and monounsaturated C17 and C19 hydrocarbons. Phylogenomic analysis placed the isolate into the family Phycisphaeraceae, class Phycisphaerae, as a new genus-level lineage. Its genome contained a gene encoding a polysaccharide lyase from the PL8 family which is probably responsible for the degradation of hyaluronic acid to a dimer, followed by its transport and hydrolysis into monomers in periplasm and final glycolytic degradation in cytoplasm. On the basis of distinct phenotypic and genomic properties, strain AB-hyl4T (DSM 117794 = UQM 41914) is proposed to be classified as
Natronomicrosphaera hydrolytica gen. nov., sp. nov.

Na.tro.no.ar.chae.a.ce’ae. N.L. neut. n. Natronoarchaeum, the type genus of the family; L. fem. pl. n. suff. -aceae, ending to denote a family; N.L. fem. pl. n. Natronoarchaeaceae, the family of the genus Natronoarchaeum.
The family Natronoarchaeaceae is a member of the order Halobacteriales, class Halobacteria, and is formed on the basis of phylogenomic analyses. It includes extremely halophilic and either aerobic or facultatively anaerobic archaea with variable key functionality, such as anaerobic sulfur respiration and potential to utilize various polysaccharides as growth substrates. The family currently contains four genera: the type genus Natronoarchaeum and the genera Salinarchaeum, Halostella, and Natranaeroarchaeum from various hypersaline
habitats.
DNA G+C content (mol%): 60.8–68.2 (whole genome sequences).
Type genus: Natronoarchaeum Shimane et al. 2010VP emend. Qui et al. 2014.

The family Desulfurivibrionaceae includes obligately anaerobic, moderately salt-tolerant, obligately alkaliphilic chemolithoautotrophic bacteria with a unique energy metabolism consisting of elemental sulfur disproportionation. H₂ or formate can also serve as additional electron donors for sulfur reduction, while nitrate can be ammonified with either sulfide or formate as the electron donors. The cultured representatives are found exclusively in saline soda lakes. The family consists of a single genus Desulfurivibrio with the type species D. alkaliphilus and a second yet undescribed species “D. dismutans” DNA G+C content (%): 60.0-60.3 (whole genome sequences)
Type genus : Desulfurivibrio Sorokin et al. 2008, VL123

Cy.clo.na.tron.a’ce.ae N.L. neut. n. Cyclonatronum, type genus of the family; L. fem. pl. n. suff. -aceae, ending to denote a family; N.L. fem. pl. n. Cyclonatronaceae, the Cyclonatronum family.
The family Cyclonatronaceae is amember of the order Balneolales, class Rhodothermia, and phylum Bacteroidota. It includes heterotrophic bacteria with either aerobic or fermentative metabolism that utilize peptides or sugars as growth substrates. The known members of the family are mesophilic, moderately salt-tolerant, chloride-independent, and obligate alkaliphiles found in saline soda lakes in Central Asia. The family currently includes two genera, the type genus Cyclonatronum and the genus Natronogracilivirga, both represented by a single species.
DNA G+C content (mol%): 49.7–51.5 (whole genome sequences).
Type genus: Cyclonatronum Zhilina et al. 2023, VL211.

The author regrets that there were errors in the JCM collection numbers in the Abstract and the protologue Table 3 of the paper by Sorokin et al. (Syst. Appl. Microbiol. 2024, 47, 126519). The correct JCM collection numbers should be: JCM 35396 and JCM 35397 instead of JCM 335396 and JCM 335397.

Natr.an.aer.o.vir.ga’ce.ae N.L. fem. n. Natranaerovirga, the type genus of the family, -aceae ending to denote a family; N.L. fem. pl. n. Natranaerovirgaceae, the Natranaerovirga family. The family Natranaerovirgaceae includes obligately
anaerobic fermentative bacteria from soda lakes. They are highly salt-tolerant alkaliphiles utilizing carbohydrates as energy and carbon source. The family belongs to the order “Lachnospirales,” class Clostridia, and consists of a single genus Natranaerovirga. The family-level status was established by phylogenomic
analysis based on the Genome Taxonomy Database classification (GDTB).
DNA G +C content (mol%): 31.3–32.3 (whole-genome sequence).
Type genus: Natranaerovirga Sorokin et al. 2012,  VL145.

Cy.clo.na.tro’num. Gr. masc. n. kyklos, a circle; N.L.neut. n. natron, soda; N.L. neut. n. Cyclonatronum,circle-shaped and soda-loving.
The genus Cyclonatronum is a member of theclass Rhodothermia of the phylum Bacteroidota. Itincludes obligately aerobic organoheterotrophs that mostly utilize proteins and peptides, and possess an active sodium-pumping proteorhodopsin. The genus currently includes a single species, Cyclonatronum proteinivorum, which is represented by a mesophilic, moderately salt-tolerant, chloride-independent, and obligate alkaliphile found in saline soda lakes in Central Asia.
DNA G +C content (mol%): 51.5 (genome sequence).
Type species: Cyclonatronum proteinivorum Zhilina et al. 2023, VL211.

Nitrate leaching from agricultural soils is increasingly found in groundwater, a primary source of drinking water worldwide. This nitrate influx can potentially stimulate the biological oxidation of iron in anoxic groundwater reservoirs. Nitrate-dependent iron-oxidizing (NDFO) bacteria have been extensively studied in laboratory settings, yet their ecophysiology in natural environments remains largely unknown. To this end, we established a pilot-scale filter on nitrate-rich groundwater to elucidate the structure and metabolism of nitrate-reducing iron-oxidizing microbiomes under oligotrophic conditions mimicking natural groundwaters. The enriched community stoichiometrically removed iron and nitrate consistently with the NDFO metabolism. Genome-resolved metagenomics revealed the underlying metabolic network between the dominant iron-dependent denitrifying autotrophs and the less abundant organoheterotrophs. The most abundant genome belonged to a new Candidate order, named Siderophiliales. This new species, “Candidatus Siderophilus nitratireducens,” carries genes central genes to iron oxidation (cytochrome c cyc2), carbon fixation (rbc), and for the sole periplasmic nitrate reductase (nap). Using thermodynamics, we demonstrate that iron oxidation coupled to nap based dissimilatory reduction of nitrate to nitrite is energetically favorable under realistic Fe3+/Fe2+ and NO3−/NO2− concentration ratios. Ultimately, by bridging the gap between laboratory investigations and nitrate real-world conditions, this study provides insights into the intricate interplay between nitrate and iron in groundwater ecosystems, and expands our understanding of NDFOs taxonomic diversity and ecological role.

Soda lakes are unique double-extreme habitats characterized by high salinity and soluble carbonate alkalinity, yet harboring rich prokaryotic life. Despite intensive microbiology studies, little is known about the identity of the soda lake hydrolytic bacteria responsible for the primary degradation of the biomass organic matter, in particular cellulose. In this study, aerobic and anaerobic enrichment cultures with three forms of native insoluble cellulose inoculated with sediments from five soda lakes in south-western Siberia resulted in the isolation of four cellulotrophic haloalkaliphilic bacteria and their four saccharolytic satellites. The final aerobic enrichment included a cellulotrophic bacteroidetes (strain ABcell3) related to Sporocytophaga accompanied by a hemicellulolytic Marinimicrobium strain ABcell2.
The anaerobic enrichments resolved in three primary cellulotrophic bacteria and their three saccharolytic bacteroidetes satellites. The culture selected on amorphous cellulose (ac) included a new cellulotrophic member of the Chitinispirillaceae (Fibrobacterota)—strain ANBcel5, and two different saccharolytic satellites from the Marinilabiliales and Balneolales orders. The final enrichment selected on Sigma 101 cellulose consisted of an endospore-forming cellulotrophic strain ANBcel31 belonging to the genus Herbivorax (Acetivibrionales) and its saccharolytic satellite from the Balneolales order. The anaerobic enrichment on a filter paper yielded a binary consortium with the cellulotrophic endospore-forming Halanaerobiales strain ANBcel28 in obligate syntrophy with a cellobiose-utilizing Natronincola. A functional genome analysis of the cellulotrophic isolates confirmed the presence of a large repertoire of genes encoding excreted cellulases, mostly from the GH9 and GH5 families, and indicated that in the endospore-forming anaerobic strains, ANBcel28 and ANBcel31 most of their endo-glucanases are assembled in cellulosomes. Overall, this study showed that cellulose can be mineralized in soda lakes at moderately saline and highly alkaline conditions either by aerobic or fermentative haloalkaliphilic bacteria.

Natr.an.aer.o.ar.chae’um N.L. neut. n. natron, soda; from Arabic n. natrun, soda, sodium carbonate; Gr. pref. an-, not (here: inseparable prefix); Gr. masc. n. aêr air; Gr. masc. adj. archaîos, ancient; N.L. neut. n. Natranaeroarchaeum, anaerobic natronophilic
archaeon. The genus Natranaeroarchaeum is classified as a member of the family Natronoarchaeaceae, order Halobacteriales, and class Halobacteria, according to phylogenomic analyses. It includes extremely halophilic and facultatively aerobic, obligately alkaliphilic, and saccharolytic archaea, capable of anaerobic sulfur respiration with sugars and starch as carbon and energy sources. The genus currently includes two species, the type species Natranaeroarchaeum sulfidigenes and Natranaeroarchaeum aerophilum, originating from hypersaline soda lakes. The DNA G+C content is 60.8–61.0 (whole-genome sequences). The genus three-letter abbreviation is Naa.
DNA G +C content (%): 60.8–61.0 (whole-genome sequences of type strains).
Type species: Natranaeroarchaeum sulfidigenes Sorokin et al. 2022a, VL211.
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The genus Natronospira is represented by a single species of extremely salt-tolerant aerobic alkaliphilic proteolytic bacterium, isolated from hypersaline soda lakes. When cells of Gram-positive cocci were used as a substrate instead of proteins at extremely haloalkaline conditions, two new members of this genus were enriched and isolated in pure culture from the same sites. Strains AB-CW1 and AB-CW4 are obligate aerobic heterotrophic proteolytic bacteria able to feed on both live and dead cells of staphylococci and a range of proteins and peptides. Similar to the type species, N. proteinivora, the isolates are extremely salt-tolerant obligate alkaliphiles. However, N. proteinivora was unable to use bacterial cells as a substrate. Electron microscopy showed direct contact between the prey and predator cells. Functional analysis of the AB-CW1 and AB-CW4 genomes identified two sets of genes coding for extracellular enzymes potentially involved in the predation and proteolysis, respectively. The first set includes several copies of lysozyme-like GH23 peptidoglycan-lyase and murein-specific M23 [Zn]-di-peptidase enabling the cell wall degradation. The second set features multiple copies of secreted serine and metallopeptidases apparently allowing for the strong proteolytic phenotype. Phylogenomic analysis placed the isolates into the genus Natronospira as two novel species members, and furthermore indicated that this genus forms a deep-branching lineage of a new family (Natronospiraceae) and order (Natronospirales) within the class Gammaproteobacteria. On the basis of distinct phenotypic and genomic properties, strain AB-CW1T (JCM 335396 = UQM 41579) is proposed to be classified as Natronospira elongata sp. nov., and AB-CW4T (JCM 335397 = UQM 41580) as Natronospira bacteriovora sp. nov.

Thi.o.ha.lo.phi.la.ce’ae N.L. masc. n. Thiohalophilus, the type genus of the family, -aceae ending to denote a family; N.L. fem. pl. n. Thiohalophilaceae the Thiohalophilus family.
The family Thiohalophilaceae incorporates aerobic, chemolithoautotrophic, sulfur-oxidizing bacteria from hypersaline habitats. They are moderate halophiles utilizing reduced sulfur compounds as the energy source with either O₂ or nitrite as the electron acceptors. The family is a member of the order Thiohalomonadales in the Gammaproteobacteria and consists of a single genus Thiohalophilus. The family-level classification in the order Thiohalomonadales was established by phylogenomic analysis according to the Genome Taxonomy DataBase method. DNA G +C content: 57.4 (genome of the type strain). Type genus: Thiohalophilus Sorokin et al. 2007, VL117.
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Me.thy.lo.ha.lo.mo.nad.al’es N.L. fem. n. Methylohalomonas, the type genus of the order; L. fem. pl. n. suff.-ales, ending to denote an order; N.L. fem. pl. n. Methylohalomonadales, order of the genus the Methylohalomonas.
The order Methylohalomonadales includes obligately methylotrophic bacteria from hypersaline salt lakes. They are moderately halophilic aerobes utilizing C1
compounds as energy and carbon sources via the serine cycle. The order forms a deep-branching phylogenetic lineage in the Gammaproteobacteria and consists
of a single family Methylohalomonadaceae and genus Methylohalomonas. The order-level classification was established by phylogenomic analysis based on the
Genome Taxonomy DataBase classification. Type genus: Methylohalomonas Sorokin et al. 2007VP.

Thi.o.ha.lo.spir.a.ce’ae N.L. fem. n. Thiohalospira, the type genus of the family, -aceae ending to denote a family; N.L. fem. pl. n. Thiohalospiraceae, the Thiohalospira family.
The family Thiohalospiraceae incorporates aerobic, chemolithoautotrophic, sulfur-oxidizing bacteria from hypersaline habitats. They are moderate to extremely halophilic aerobes utilizing reduced sulfur compounds as the energy source and assimilating CO₂ via the Calvin–Benson–Bassham cycle. The family is a
member of the order Thiohalospirales in the Gammaproteobacteria and consists of a single genus Thiohalospira. The family-level status was established by phylogenomic analysis based on the Genome Taxonomy DataBase classification.
DNA G + C content (%): (65.6–69.1) (Tm and genome sequence of the type species). Type genus: Thiohalospira Sorokin et al. 2008^VP.

Na.tro.no.cel’la; N.L. neut. n. natron (arbitrarily derived from the Arabic n. natrun or natron), soda, sodium carbonate; N.L. pref. natrono-, pertaining to soda; L. fem. n. cella, a room, a cell in biology; N.L. fem. n. Natronocella, a soda-loving cell.The genus Natronocella comprise aerobic heterotrophs that utilizes short-chain nitriles and their corresponding fatty acids and amides as energy, carbon,
and nitrogen sources. Natronocella is a moderately salt-tolerant, chloride-independent obligate alkaliphile inhabiting soda lakes in Central Asia. The genus currently includes a single species N. acetinitrilica. It was originally classified as a member of the family Ectothiorhodospiraceae, order Chromatiales, class Gammaproteobacteria, but more recent phylogenomic analyses classify it in the proposed order “Nitrococcales” and family “Aquisalimonadaceae.” DNA G+C content (%): 63.0 (genome sequence).Type species: Natronocella acetinitrilica Sorokin et al. 2007, VL116.

Thi.o.ha.lo.spir.al’es N.L. fem. n. Thiohalospira, the type genus of the order; L. fem. pl. n. suff. -ales, ending to denote an order; N.L. fem. pl. n. Thiohalospirales, the order of the genus Thiohalospira.
The order Thiohalospirales accommodates aerobic, chemolithoautotrophic, sulfur-oxidizing halophilic bacteria from hypersaline habitats which assimilate
CO₂ via the Calvin–Benson-Bassham cycle. The order is a deeply branching lineage of the Gammaproteobacteria and consists of a single family Thiohalospiraceae and genus Thiohalospira. The order-level status was established by phylogenomic analysis based on the Genome Taxonomy DataBase classification. Type genus: Thiohalospira Sorokin et al. 2008^VP.

Cells of Methylohalomonas are nonmotile rods, 0.4–0.5 × 1–4 μm, with a Gram-negative type of cell wall and dividing by binary fission. The dominant membrane polar lipid fatty acids are saturated C16:0 and C17:0. It is an aerobic, obligate methylotroph utilizing only methanol, formate, and methylamine
as growth substrates. The carbon is assimilated via serine cycle. It is a neutrophilic halophile growing optimally at 2M NaCl, pH 7.5, and 35∘C. The genus includes a single species represented by a single strain isolated from hypersaline southwestern Siberian steppe lakes (Sorokin et al., 2007). It represents a new family “Methylohalomonadaceae” within a new order “Methylohalomonadales” in the Gammaproteobacteria. DNA G + C content (%): 59.4 (genome sequence). Type species: Methylohalomonas lacus Sorokin et al. 2007VP. Number of species with validly published name: 1. Family classification: The genus Methyhalomonas is classified within the new family Methylohalomonadaceae.

Natr. ar. chae. o. ba' cu. lum. N.L. neut. n. natron, soda, sodium carbonate (arbitrarily derived from Arabic n. natrun or natron) ; N.L. pref. natro- pertaining to soda; Gr. masc. adj. archaîos ancient; L. neut. n. baculum, small stick, rod; N.L. neut. n. Natrarchaeobaculum soda-loving archaeal rod.

The genus Natrarchaeobaculum is classified as a member of the family Natrialbaceae, order Natrialbales, class Halobacteria according to phylogenomic analyses. It includes extremely halophilic heterotrophic natronoarchaea, some of which can grow anaerobically by sulfur respiration utilizing organic acids, H2 and formate as the electron donors. The genus currently includes two species: the facultatively anaerobic type species Natrarchaeobaculum sulfurireducens and the aerobic species Natrarchaeobaculum aegyptiacus. Inhabits hypersaline soda lakes. The DNA G + C content is 62.8-64.1 % (genome sequence). Three letter abbreviation is Nab.