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

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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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

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

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

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

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

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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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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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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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

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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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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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.@en

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.@en

Thi.o.ha.lo.bac.ter.a.ce’ae N.L. masc. n. Thiohalobacter, the type genus of the family, -aceae ending to denote a family; N.L. fem. pl. n. Thiohalobacteraceae the
Thiohalobacter family. The family Thiohalobacteraceae consists of aerobic, chemolithoautotrophic, sulfur-oxidizing bacteria from hypersaline salt lakes. They are moderately halophilic aerobic, bacteria 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 Thiohalobacterales within the Gammaproteobacteria and consists of a single genus Thiohalobacter. The family-level status was established by phylogenomic analysis based on the Genome Taxonomy DataBase classification. DNA G + C content (%): 64.2 (genome sequence). Type genus: Thiohalobacter Sorokin et al. 2010^VP.@en

A spiral-shaped, highly motile bacterium was isolated from freshwater sulfidic sediment. Strain J10 ^T is a facultative autotroph utilizing sulfide, thiosulfate, and sulfur as the electron donors in microoxic conditions. Despite high 16S rRNA gene sequence sequence identity to Magnetospirillum gryphiswaldense MSR-1 ^T (99.6 %), digital DNA-DNA hybridisation homology and average nucleotide identity between the two strains was of the different species level (25 % and 83 %, respectively). Strain J10 ^T is not magnetotactic. The DNA G + C content of strain J10 ^T is 61.9 %. The predominant phospholipid ester-linked fatty acids are C18:1ω7, C16:1ω7, and C16:0. Strain J10 ^T (=DSM 23205 ^T = VKM B-3486 ^T) is the first strain of the genus Magnetospirillum showing lithoautotrophic growth and is proposed here as a novel species, Magnetospirillum sulfuroxidans sp. nov. In addition, we propose to establish a framework for distinguishing genera and families within the order Rhodospirillales based on phylogenomic analysis using the threshold values for average amino acid identity at ̴ 72 % for genera and ̴ 60 % for families. According to this, we propose to divide the existing genus Magnetospirillum into three genera: Magnetospirillum, Paramagnetospirillum, and Phaeospirillum, constituting a separate family Magnetospirillaceae fam. nov. in the order Rhodospirillales. Furthermore, phylogenomic data suggest that this order should accomodate six more new family level groups including Magnetospiraceae fam. nov., Magnetovibrionaceae fam. nov., Dongiaceae fam. nov., Niveispirillaceae fam. nov., Fodinicurvataceae fam. nov., and Oceanibaculaceae fam. nov.

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Extremely halophilic archaea are one of the principal microbial community components in hypersaline environments. The majority of cultivated haloarchaea are aerobic heterotrophs using peptides or simple sugars as carbon and energy sources. At the same time, a number of novel metabolic capacities of these extremophiles were discovered recently among which is a capability of growing on insoluble polysaccharides such as cellulose and chitin. Still, polysaccharidolytic strains are in minority among cultivated haloarchaea and their capacities of hydrolyzing recalcitrant polysaccharides are hardly investigated. This includes the mechanisms and enzymes involved in cellulose degradation, which are well studied for bacterial species, while almost unexplored in archaea and haloarchaea in particular. To fill this gap, a comparative genomic analysis of 155 cultivated representatives of halo(natrono)archaea, including seven cellulotrophic strains belonging to the genera Natronobiforma, Natronolimnobius, Natrarchaeobius, Halosimplex, Halomicrobium and Halococcoides was performed. The analysis revealed a number of cellulases, encoded in the genomes of cellulotrophic strains but also in several haloarchaea, for which the capacity to grow on cellulose was not shown. Surprisingly, the cellulases genes, especially of GH5, GH9 and GH12 families, were significantly overrepresented in the cellulotrophic haloarchaea genomes in comparison with other cellulotrophic archaea and even cellulotrophic bacteria. Besides cellulases, the genes for GH10 and GH51 families were also abundant in the genomes of cellulotrophic haloarchaea. These results allowed to propose the genomic patterns, determining the capability of haloarchaea to grow on cellulose. The patterns helped to predict cellulotrophic capacity for several halo(natrono)archaea, and for three of them it was experimentally confirmed. Further genomic search revealed that glucose and cellooligosaccharides import occurred by means of porters and ABC (ATP-binding cassette) transporters. Intracellular glucose oxidation occurred through glycolysis or the semi-phosphorylative Entner-Dudoroff pathway which occurrence was strain-specific. Comparative analysis of CAZymes toolbox and available cultivation-based information allowed proposing two possible strategies used by haloarchaea capable of growing on cellulose: so-called specialists are more effective in degradation of cellulose while generalists are more flexible in nutrient spectra. Besides CAZymes profiles the groups differed in genome sizes, as well as in variability of mechanisms of import and central metabolism of sugars.@en

Proteomics has greatly advanced the understanding of the cellular biochemistry of microorganisms. The thermoalkaliphile Caldalkalibacillus thermarum TA2.A1 is an organism of interest for studies into how alkaliphiles adapt to their extreme lifestyles, as it can grow from pH 7.5 to pH 11. Within most classes of microbes, the membrane-bound electron transport chain (ETC) enables a great degree of adaptability and is a key part of metabolic adaptation. Knowing what membrane proteins are generally expressed is crucial as a benchmark for further studies. Unfortunately, membrane proteins are the category of proteins hardest to detect using conventional cellular proteomics protocols. In part, this is due to the hydrophobicity of membrane proteins as well as their general lower absolute abundance, which hinders detection. Here, we performed a combination of whole cell lysate proteomics and proteomics of membrane extracts solubilised with either SDS or FOS-choline-12 at various temperatures. The combined methods led to the detection of 158 membrane proteins containing at least a single transmembrane helix (TMH). Within this data set we revealed a full oxidative phosphorylation pathway as well as an alternative NADH dehydrogenase type II (Ndh-2) and a microaerophilic cytochrome oxidase ba₃. We also observed C. thermarum TA2.A1 expressing transporters for ectoine and glycine betaine, compounds that are known osmolytes that may assist in maintaining a near neutral internal pH when the external pH is highly alkaline.

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Thi.o.ha.lo.rhab.dal’es N.L. fem. n. Thiohalorhabdus, the type genus of the order; L. fem. pl. n. suff. -ales ending to denote an order; N.L. fem. pl. n. Thiohalorhabdales, order of the genus Thiohalorhabdus.
According to the phylogenomic analysis, the order Thiohalorhabdales forms a deeply branching phylogenetic lineage at the base of the Gammaproteobacteria. It consists of a single family Thiohalorhabdaceae and genus Thiohalorhabdus. The cultured members of the order are extremely halophilic, facultatively anaerobic (denitrifying), chemolithoautotrophic, sulfur-oxidizing bacteria from hypersaline habitats with neutral pH. Type genus: Thiohalorhabdus Sorokin et al. 2008^VP.@en