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.@en

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

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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.@en

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.@en

The genus Natranaerovirga is a member of the class Clostridia. It includes obligately anaerobic, fermentative heterotrophs which whose key metabolic property is the ability to utilizes polygalacturonates as growth substrates. The species of the genus are highly salt-tolerant, chloride-independent, obligate alkaliphiles found in saline soda lakes and soils in Central Asia. The genus currently includes two species: N. pectinivora, the type species of the genus, and N. hydrolytica. The DNA G+C content is 31.3-32.3 % (whole genome sequences). @en

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.@en

Beta-mannans are insoluble plant polysaccharides with beta-1,4-linked mannose as the backbone. We used three forms of this polysaccharide, namely, pure mannan, glucomannan, and galactomannan, to enrich haloarchaea, which have the ability to utilize mannans for growth. Four mannan-utilizing strains obtained in pure cultures were closely related to each other on the level of the same species. Furthermore, another strain selected from the same habitats with a soluble beta-1,4-glucan (xyloglucan) was also able to grow with mannan. The
phylogenomic analysis placed the isolates into a separate lineage of the new genus level within the family Natrialbaceae of the class Halobacteria. The strains are moderate alkaliphiles, extremely halophilic, and aerobic saccharolytics. In addition to the three beta-mannan forms, they can also grow with cellulose, xylan, and xyloglucan. Functional genome analysis of two representative strains demonstrated the presence of several genes coding for extracellular endo-beta-1,4-mannanase from the GH5_7 and 5_8 subfamilies and the GH26 family of glycosyl hydrolases. Furthermore, a large spectrum of genes encoding other glycoside hydrolases that were potentially involved in the hydrolysis of cellulose and xylan were also identified in the genomes. A comparative genomics analysis also showed the presence of similar endo-beta-1,4-mannanase homologs in the cellulotrophic genera Natronobiforma and Halococcoides. Based on the unique physiological properties and the results of phylogenomic analysis, the novel mannan-utilizing halolarchaea are proposed to be classified into a new genus and species Natronoglomus mannanivorans gen. nov., sp. nov. with the type strain AArc-m2/3/4 (=JCM 34861=UQM 41565).@en

A variety of lakes located in the dry steppe area of southwestern Siberia are exposed to rapid climatic changes, including intra-century cycles with alternating dry and wet phases driven by solar activity. As a result, the salt lakes of that region experience significant fluctuations in water level and salinity, which have an essential impact on the indigenous microbial communities. But there are few microbiological studies that have analyzed this impact, despite its importance for understanding the functioning of regional water ecosystems. This work is a retrospective study aimed at analyzing how solar activity-related changes in hydrological regime affect phototrophic microbial communities using the example of the shallow soda lake Tanatar VI, located in the Kulunda steppe (Altai Region, Russia, southwestern Siberia). The main approach used in this study was the comparison of hydrochemical and microscopic data obtained during annual field work with satellite and solar activity data for the 12-year observation period (2011–2022). The occurrence of 33 morphotypes of cyanobacteria, two key morphotypes of chlorophytes, and four morphotypes of anoxygenic phototrophic bacteria was analyzed due to their easily recognizable morphology. During the study period, the lake surface changed threefold and the salinity changed by more than an order of magnitude, which strongly correlated with the phases of the solar activity cycles. The periods of high (2011–2014; 100–250 g/L), medium (2015–2016; 60 g/L), extremely low (2017–2020; 13–16 g/L), and low (2021–2022; 23–34 g/L) salinity with unique biodiversity of phototrophic communities were distinguished. This study shows that solar activity cycles determine the dynamics of the total salinity of a southwestern Siberian soda lake, which in turn determines the communities and microorganisms that will occur in the lake, ultimately leading to cyclical changes in alternative states of the ecosystem (dynamic stability).

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Use of curldlan, an insoluble β-1,3-glucan, as an enrichment substrate under aerobic conditions resulted in the selection from hypersaline soda lakes of a single natronarchaeon, strain AArc-curdl1. This organism is an obligately aerobic saccharolytic, possessing a poorly explored (in Archaea) potential to utilize beta-1–3 glucans, being only a second example of a haloarchaeon with this ability known in pure culture. The main phenotypic property of the isolate is the ability to grow with insoluble β-1,3-backboned glucans, i.e. curdlan and pachyman. Furthermore, the strain utilized starch family α-glucans, beta-fructan inulin and a limited spectrum of sugars. The major ether-bound membrane polar phospholipids included PGP-Me and PG. The glyco- and sulfolipids were absent. The major respiratory menaquinone is MK-8:8. According to phylogenomic analysis, AArc-curdl1 represents a separate species in the recently described genus Natronosalvus within the family Natrialbaceae. The closest related species is Natronosalvus amylolyticus (ANI, AAI and DDH values of 90.2, 91.6 and 44 %, respectively). On the basis of its unique physiological properties and phylogenomic distance, strain AArc-curdl1T is classified as a novel species Natronosalvus hydrolyticus sp. nov. (=JCM 34865 = UQM 41566).@en

Na.tro.no.cal’cu.lus N.L. neut. n. natron, arbitrarily derived from the Arabic natrun or natron, soda; L. masc. n. calculus, pebble, gravel; N.L. masc. n. Natronocalculus, soda-loving pebble-shaped cells. The genus Natronocalculus is a member of the family Halorubraceae, order Haloferacales, and class Halobacteria, according to the NCBI classification, while recent
changes in the taxonomy of the Halobacteria based on the Genome Taxonomy Database phylogenomic classification place Natronocalculus into the family Haloferacaceae, order Halobacteriales. The genus members are aerobic, extremely halophilic and moderately
alkaliphilic, and saccharolytic archaea, utilizing various alpha-glucans and sugars as carbon and energy sources. The genus currently includes a single species Natronocalculus amylovorans inhabiting hypersaline soda lakes. The genus three-letter abbreviation is Ncl.
DNA G +C content (mol%): 51.5 (whole-genome sequence of the type strain).
Type species: Natronocalculus amylovorans Sorokin et al. 2022, VL211.
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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.
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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.
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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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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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Natr.an.ae.ro.fa.ba.ce’ae. N.L. fem. n. Natranaerofaba, a bacterial genus; L. fem. pl. n. suff. -aceae, ending to denote a family; N.L. fem. pl. n. Natranaerofabaceae, the family of Natranaerofaba. The family Natranaerofabaceae includes obligately anaerobic acetogenic bacteria from soda lakes. They are extremely salt-tolerant and moderately thermophilic alkaliphiles capable of anaerobic carboxydotrophy. The family belongs to the order Natranaerobiales, class Natranaerobiia, and consists of a single genus Natranaerofaba. The family-level status was established by phylogenomic analysis. DNA G + C content (%): 35.3 (whole genome sequence). Type genus: Natranaerofaba Sorokin et al. 2021, VL202.@en

Na.tro.no.ba.cil’lus N.L. neut. n. natron, soda, sodium carbonate (arbitrarily derived from the Arabic n. natrun or natron); N.L. pref. natrono-, pertaining to soda; L. masc. n. bacillus, a small rod; N.L.masc.n. Natronobacillus,
soda-loving rod. The genus Natronobacillus is classified as a member of the family "Amphibacillaceae”, order Bacillales, class Bacilli, phylum Firmicutes. It includes high salt-tolerant, obligately alkaliphilic, aerotolerant, fermentative,
saccharolytic, spore-forming anaerobes utilizing various carbohydrates as energy and carbon sources and capable of diazotrophic growth. The genus currently
includes a single species N. azotifigens represented by multiple closely related isolates from soda soils and soda lake sediments. DNA G + C content (mol%): 36.1–38.5 (Tm); 36.7 (whole genome sequence of the type strain). Type species: Natronobacillus azotifigens Sorokin et al. 2008b, VL125.@en

Climate change, desertification, salinisation of soils and the changing hydrology of the Earth are creating or modifying microbial habitats at all scales including the oceans, saline groundwaters and brine lakes. In environments that are saline or hypersaline, the biodegradation of recalcitrant plant and animal polysaccharides can be inhibited by salt-induced microbial stress and/or by limitation of the metabolic capabilities of halophilic microbes. We recently demonstrated that the chitinolytic haloarchaeon Halomicrobium can serve as the host for an ectosymbiont, nanohaloarchaeon ‘Candidatus Nanohalobium constans’. Here, we consider whether nanohaloarchaea can benefit from the haloarchaea-mediated degradation of xylan, a major hemicellulose component of wood. Using samples of natural evaporitic brines and anthropogenic solar salterns, we describe genome-inferred trophic relations in two extremely halophilic xylan-degrading three-member consortia. We succeeded in genome assembly and closure for all members of both xylan-degrading cultures and elucidated the respective food chains within these consortia. We provide evidence that ectosymbiontic nanohaloarchaea is an active ecophysiological component of extremely halophilic xylan-degrading communities (although by proxy) in hypersaline environments. In each consortium, nanohaloarchaea occur as ectosymbionts of Haloferax, which in turn act as scavenger of oligosaccharides produced by xylan-hydrolysing Halorhabdus. We further obtained and characterised the nanohaloarchaea–host associations using microscopy, multi-omics and cultivation approaches. The current study also doubled culturable nanohaloarchaeal symbionts and demonstrated that these enigmatic nano-sized archaea can be readily isolated in binary co-cultures using an appropriate enrichment strategy. We discuss the implications of xylan degradation by halophiles in biotechnology and for the United Nation's Sustainable Development Goals.

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Haloalkaliphilic chemolithoautotrophic sulfur-oxidizing bacteria belonging to the genus Thioalkalivibrio are highly abundant in microbial communities found in soda lakes and dominant in full-scale bioreactors removing sulfide from industrial waste gases. Despite certain soda lakes being remote and unaffected by anthropogenic activities, haloalkaliphilic microorganisms, including Thioalkalivibrio strains, possess various antibiotic resistance genes. In this study, we investigated the impact of the antibiotic ampicillin on a co-culture of two Thioalkalivibrio species, Tv. thiocyanoxidans ARh2^T and Tv. versutus AL2^T, both experimentally and through in silico analysis of antibiotic resistance. Cell growth dynamics were monitored over time at increasing ampicillin concentrations using rep- and qPCR. Within ten days after the addition of ampicillin, the co-culture transitioned from a Tv. thiocyanoxidans ARh2^T-dominated to a stable Tv. versutus AL2^T-dominated culture. This shift was attributed to Tv. versutus AL2^T displaying a lower susceptibility to ampicillin, making it more competitive. These results emphasize the potential implications of antibiotic pressure on microbial communities, where a resistant species can outcompete a stable co-culture. This study presents the first evidence of such dynamics in haloalkaliphilic chemolithoautotrophs. By understanding the antibiotic resistance and the competitive dynamics of haloalkaliphilic bacteria like Thioalkalivibrio, we can gain insights into their behaviour and stress response.

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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.@en

Thi.o.ha.lo.bac.ter.al’es N.L. masc. n. Thiohalobacter, the type genus of the order; L. fem. pl. n. suff. -ales, ending to denote an order; N.L. fem. pl. n. Thiohalobacterales, the order of the genus Thiohalobacter.
The order Thiohalobacterales accommodates obligately chemolithoautotrophic aerobic bacteria utilizing inorganic sulfur compounds as the energy source and assimilating CO₂ via the Calvin–Benson–Bassham cycle. The order is a deeply branching member of the Gammaproteobacteria and consists of two families
Thiohalobacteraceae and Thiogranaceae, both of which include one genus. The order-level status was established by phylogenomic analysis based on the Genome Taxonomy DataBase classification. Type genus: Thiohalobacter Sorokin et al. 2010^VP.
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