Two extremely halophilic archaeal strains, HT40T and LN261T, were isolated from salt crystal samples collected from the Dingyuan Salt Mine in Anhui, China. Strain HT40T was found to possess two copies of the 16 S rRNA gene (rrnA and rrnB), while only one copy was detected in strain LN261T. Phylogenetic analysis based on the 16 S rRNA gene sequences revealed that the rrnA and rrnB genes of HT40T showed high sequence similarities with Halovenus aranensis EB27T (94.73

Two halophilic archaeal strains, AD34T and PAK95, were isolated from a salt mine in Yunnan and rock salt in Jiangsu, two provinces in China that are 2,000 km apart, respectively. Cells of strain AD34T were spherical while those of PAK95 were rod-shaped. Strains AD34T and PAK95 were Gram-stain-negative, aerobic and able to grow at 1.4-4.8 M NaCl (with optimum at 3.1 M NaCl), pH 5.0-9.0 (optimum, pH 7.5) and 20-60 °C (optimum, 37 °C and 40 °C, respectively). Their 16S rRNA gene sequences showed the closest similarity to Haloparvum sedimenti DYS4T, with similarities of 95.11% (AD34T) and 95.46% (PAK95). The rpoB' gene sequences of strains AD34T and PAK95 showed the highest similarity to species of Haloparvum alkalitolerans MK62-1T with 91.40% (PAK95) and 91.53% (AD34T) identity. Comprehensive phylogenetic analyses revealed that strains AD34T and PAK95 form a robust, monophyletic clade with 100% bootstrap support, clearly distinct from related genera, particularly from the genus Haloparvum. From whole-genome sequencing, the DNA G+C content of AD34T and PAK95 is 66.5 and 66.4 mol%, respectively, while that of DYS4T and MK62-1T is 68.3 and 69.1 mol%, respectively. The average nucleotide identity between AD34T, PAK95 and the family Haloferacaceae ranged from 66.5 to 79.2%. The digital DNA-DNA hybridization values ranged from 19.6 to 32.8%, while the average amino acid identity (AAI) values were between 58.0 and 72.0%. Strains AD34T and PAK95 may represent a novel species of a novel genus within the family Haloferacaceae, as judged by the AAI cutoff value (≤72.1%) proposed for differentiating genera within this family. The major polar lipids of strain AD34T were phosphatidylglycerol (PG), PG phosphate methyl ester, PG sulphate and sulphated mannosyl glucosyl diether. Based on the phenotypic and phylogenetic analyses, it is proposed that strains AD34T (=MCCC 4K00176T=KCTC 4324T) and PAK95 (=MCCC 4K00231=CGMCC 1.62791=KCTC 4376) represent a novel genus and species within the family Haloferacaceae, for which the name Halosubterraneus shenae gen. nov., sp. nov. is proposed. The type strain is AD34T.

Coastal tidal flats represent dynamic saline environments that harbor largely unexplored haloarchaeal communities. In this study, amplicon sequencing, metagenomic analyses, and cultivation-based approaches revealed substantial haloarchaeal diversity in tidal flats from four provinces of eastern China despite their relatively low salinity. Five haloarchaeal strains, designated YSMS36T, DYSN1, QDMS2, CMSO5T, and ZSTT2, were isolated from diverse tidal flats. Theses strains shared 16S rRNA gene sequence similarities of 92.1-92.2% with their closest validly named relative, Salinilacihabitans rarus AD-4T. Phylogenetic analyses based on 16S rRNA and rpoB' gene sequences showed that the five strains formed a distinct and well-supported monophyletic lineage, separated from currently recognized members of the class Halobacteria. Average amino acid identity (AAI), average nucleotide identity (ANI), and digital DNA-DNA hybridization (dDDH) values between these five strains and the related Halobacteria representatives were 49.3-62.7%, 66.9-74.9%, and 16.2-29.5%, respectively, and well below the accepted thresholds for species and genus delineation. Phylogenomic analyses further supported their placement within a novel family of the order Halobacteriales. Based on phylogenetic, genomic, chemotaxonomic, and phenotypic analyses, these five strains represent two novel species of a novel genus within a novel family. The names, Halolitoreaceae fam. nov., Halolitoreus marinus gen. nov., sp. nov., and Halolitoreus rarus sp. nov. are herein proposed.

Six novel halophilic archaeal strains, DFWS5T, DT45T, DYHT-AS-18T, HRN-SO-5T, TZWSO28, and TZWWS8T were isolated from tidal flats and saline-alkali soil collected from the eastern coastal region of China. Amplicon sequencing and metagenomic analyses indicated that these strains were present at low abundance in their original habitats, with only three strains detected by culture-independent approaches. These six strains constituted an independent clade alongside members of the genus Haloarchaeobius based on the 16S rRNA gene phylogeny. Except for the comparison between strains DYHT-AS-18T and TZWSO28, the average nucleotide identity, digital DNA-DNA hybridization, and average amino acid identity values among these strains and existing members of the genus Haloarchaeobius were 76.60-89.50%, 21.00-38.50%, and 67.99-88.76%, respectively, below the proposed thresholds for species delineation. In contrast, these three values between strains DYHT-AS-18T and TZWSO28 were 97.36%, 76.30%, and 97.25%, respectively, exceeding the proposed thresholds. Phylogenomic analysis revealed that the six strains clustered with members of the genus Haloarchaeobius, but formed distinct branches separate from the current species. The optimal growth conditions for these six strains in terms of NaCl, MgCl2, temperature, and pH were 0.9-4.8 M, 0-1 M, 20-50 °C, and 5.0-9.5, respectively. According to phenotypic differences in nutrition and biochemical activity, these six strains can be distinguished from their related species. On the basis of polyphasic taxonomic evidence, five novel species within the genus Haloarchaeobius are proposed to accommodate strains DFWS5T, DT45T, DYHT-AS-18T, HRN-SO-5T, TZWSO28, and TZWWS8T, respectively.

Five novel halophilic archaeal strains, designated DTA46T, DTA98T, HHNYT27T, N11T, and SY-15T, were isolated from diverse saline environments across various regions of China. Amplicon and metagenome analyses revealed that three amplicon reads were affiliated with strains DTA46T, HHNYT27T, and N11T while two MAGs related to strains N11T and SY-15T. The sequence similarities among these five strains and current species of the genus Halorubrum were 93.1%-99.1% and 86.0%-95.9% judged by 16S rRNA and rpoB' genes, respectively. Phylogenomic and comparative genomic analyses revealed their close affiliation with Halorubrum. The average nucleotide identity (ANI), digital DNA-DNA hybridization (dDDH), and average amino acid identity (AAI) values between these strains and existing Halorubrum species ranged from 74.9%-93.6%, 22.3%-58.3%, and 68.3%-93.7%, respectively. All are below the recommended thresholds for species delineation, which supports their classification as novel taxa. The growth characteristics of strains DTA46T, DTA98T, HHNYT27T, N11T, and SY-15T were determined as follows: temperature range 20-60 °C (optima: 35, 37-42, 37, 35, and 42 °C), NaCl concentration 1.4-5.5 M (optima: 2.6, 3.1, 3.1, 3.1, and 5.1 M), and pH range 5.5-9.5 (optima: 8.0, 8.0, 7.0, 7.5, and 7.0). Based on the polyphasic characterization integrating phenotypic, chemotaxonomic, phylogenetic, and phylogenomic evidence, strains DTA46T, DTA98T, HHNYT27T, N11T, and SY-15T are proposed to represent five novel species of the genus Halorubrum, for which the names Halorubrum marinum sp. nov., Halorubrum rarum sp. nov., Halorubrum wangae sp. nov., Halorubrum shenae sp. nov., and Halorubrum zhoui sp. nov. are designated, respectively.

Six novel halophilic archaeal strains, DFWS20T, NG-SE-30T, NG-WS-4T, HHT-WS-8, NG-SE-24T, and SG-WS-1, were isolated from different coastal regions of China. Metagenome and amplicon analyses showed that the abundance of archaea in the corresponding samples was very low. Strains DFWS20T, NG-SE-30T, NG-WS-4T, and HHT-WS-8 were found to cluster with current Haladaptatus species, while strains NG-SE-24T and SG-WS-1 with those of Halomicrococcus based on 16S rRNA and rpoB' gene phylogenies. The overall-genome related indexes (OGRIs), average nucleotide identity (ANI), digital DNA-DNA hybridization (dDDH), and average amino acid identity (AAI) values, between strains DFWS20T, NG-SE-30T, NG-WS-4T, HHT-WS-8, and Haladaptatus species were 77.0-83.1%, 22.2-28.3%, and 74.7-84.8%, while those between strains NG-SE-24T, SG-WS-1, and Halomicrococcus species were 79.6-94.9%, 26.0-63.9%, and 76.5-94.1%, respectively. These values were lower than the threshold of species classification. In contrast, the OGRIs between strains NG-WS-4T and HHT-WS-8, as well as those between strains NG-SE-24T and SG-WS-1, were above the threshold of species classification. Diverse differential phenotypic characteristics, such as nutrition, biochemical activities, and antibiotic sensitivity, were determined in these six strains and the existing species of the corresponding genera. The most abundant pathways in the genera Haladaptatus and Halomicrococcus were related to carbohydrate metabolism and amino acid metabolism. Based on the natural habitat analysis of the 16S rRNA genes of the strains, their target sequences were primarily found in habitats such as aquatic, soil, sediments, plant, and marine environments. The major polar lipids of strains DFWS20T, NG-SE-30T, NG-WS-4T, and HHT-WS-8 were phosphatidylglycerol (PG), phosphatidylglycerol phosphate methyl ester (PGP-Me), phosphatidylglycerol sulfate (PGS), and sulfated mannosyl glucosyl diether (S-DGD-1), while those of strains NG-SE-24T and SG-WS-1 were PG, PGP-Me, S-DGD-1, and galactosyl mannosyl glucosyl diether (TGD-2). Based on these polyphasic classification, strains DFWS20T, NG-SE-30T, NG-WS-4T, and HHT-WS-8 represent three novel species of the genus Haladaptatus while NG-SE-24T and SG-WS-1 represent a novel species of the genus Halomicrococcus.

Seven novel halophilic archaeal strains DYHT-AS-1T, GDY60T, TS25T, XH63T, SHR40T, SYNS179T, and ZY30T were isolated from tidal flat, saline lakes, marine solar saltern and coarse sea salts from different regions of China. Metagenomic and amplicon analyses indicated that the abundance of these seven strains in respective habitats was low. Phylogenetic and comparative genomic analyses indicated that strains DYHT-AS-1T, GDY60T, TS25T, and XH63T formed a tight cluster with Halosimplex species, exhibiting high 16S rRNA gene sequence similarity (90.4-99.4 %). The ANI, dDDH, and AAI values among these four strains and current Halosimplex species were 80.8-92.3 %, 24.5-53.3 %, and 77.8-91.5 %, respectively. Strains SHR40T, SYNS179T, and ZY30T were related to Halovenus species, with 16S rRNA gene sequence similarities ranging from 88.8 % to 98.4 %. The ANI, dDDH, and AAI values among these three strains and current Halovenus species were 69.9-77.8 %, 19.4-21.5 %, and 62.1-78.1 %, respectively. These values are significantly lower than the thresholds for species demarcation. The optimal growth conditions for these seven strains in terms of NaCl, MgCl₂, temperature, and pH were 3.1-3.4 M, 0.05-0.5 M, 35-40 °C, and 6.5-7.5, respectively. According to phenotypic differences in nutrition, biochemical activity, and antibiotic sensitivity, these seven strains can be distinguished from their related species. Based on the above results, strains DYHT-AS-1T, GDY60T, TS25T, and XH63T represent four new species of the genus Halosimplex, and strains SHR40T, SYNS179T, and ZY30T represent three novel species of the genus Halovenus.

Four novel halophilic archaeal strains, DTA7T, DTA28T, FCH18aT, and WLHS9T, were isolated from a coastal saline-alkali land and two saline lakes in China. The metagenomic analyses revealed that the coastal saline-alkali land from Dongtai tidal flat the highest relative abundance of archaea compared to the saline sediment samples of Feicui Salt Lake and Wulanhushao Salt Lake. These four strains showed high sequence similarities to current species within the genus Natronorubrum judged by 16S rRNA gene and rpoB' gene sequence similarities, and formed tight clusters with current Natronorubrum species based on the phylogenies of these two house-keeping genes. Phylogenomic analysis confirmed the phylogenies based on 16S rRNA gene and rpoB' genes. Comparative genomic analysis revealed that the average nucleotide identity (ANI), digital DNA-DNA hybridization (dDDH), and average amino acid identity (AAI) values among these four strains and existing species of the genus Natronorubrum were 76.8-92.7 %, 22.8-52.7 %, and 73.4-94.7 %, respectively. These overall genome-related indexes were significantly below the thresholds for species delineation. These four strains showed optimal growth at 1.7-3.1 M NaCl, 37 °C, and pH 7.0-9.5. Strain WLHS9T was found to be a neutrophilic halophile, while the others exhibited alkaliphilic halophilic characteristics. The major phospholipids detected in these four strains included phosphatidic acid (PA), phosphatidylglycerol (PG), and phosphatidylglycerol phosphate methyl ester (PGP-Me). The glycolipid of strain WLHS9T was identical to that of the current neutrophilic species of Natronorubrum. Based on phylogenetic analysis, phenotypic characteristics, polar lipid profiles, and phylogenomic data, strains DTA7T, DTA28T, FCH18aT, and WLHS9T represent four novel species within the genus, namely, Natronorubrum marinum sp. nov., Natronorubrum amylolyticum sp. nov., Natronorubrum halobium sp. nov., and Natronorubrum salinum sp. nov., respectively.

Four halophilic archaeal strains were isolated from sea salt and a saline lake in China. Based on phylogenetic and phylogenomic analyses, the four strains are related to the genera of Halobellus, Halobaculum, and Halorarum within the family Haloferacaceae. The four strains possess genes responsible for carotenoid synthesis, maintenance of a high internal salt concentration, as well as diverse enzymes with biotechnological potential. The average nucleotide identity (ANI), average amino acid identity (AAI), and digital DNA-DNA hybridization (dDDH) values among these four strains and their related species were lower than the established thresholds proposed for species demarcation. Strains DFY28T, ZY16T, QDC11T, and XH14T were distinguished from related species based on a variety of phenotypic characteristics. The major polar lipids of these four strains were similar to those of respective relatives within the genera Halobellus, Halobaculum, and Halorarum. The phenotypic, phylogenetic, and genome-based analyses suggest that strains DFY28T (= CGMCC 1.17470T = JCM 34310T), ZY16T (= CGMCC 1.17476T = JCM 34311T), QDC11T (= MCCC 4K00127T = KCTC 4308T), and XH14T (= CGMCC 1.17028T = JCM 34145T) represent four novel species of the genera Halobellus, Halobaculum and Halorarum, for which the names Halobellus marinus sp. nov., Halobellus ordinarius sp. nov., Halobaculum rarum sp. nov., and Halorarum halobium sp. nov. are proposed.

A new family related to the family Haloarculaceae was proposed and the genus Actinarchaeum was merged into the genus Halocatena through phylogenetic, phylogenomic, and comparative genomic analyses. Four strains KK48T, YCN56T, SYNS191T, and SYNS196T with new taxonomic status were isolated from inland saline lakes and a marine solar saltern. According to the comparison of 16S rRNA gene and rpoB' gene sequences, strains KK48T, YCN56T, SYNS191T, and SYNS196T showed high sequence similarities to the genera Salinibaculum and Salinirubellus, respectively. The values of average nucleotide identity, digital DNA-DNA hybridization, and average amino acid identity between these strains and the species of Salinibaculum and Salinirubellus ranged from 75.3 to 77.7 %, 24.5-25.9 % and 66.3-73.4 %, respectively. These data were well below the threshold for species classification, supporting their placements in new taxa. The major polar lipids of these strains were phosphatidic acid, phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, phosphatidylglycerol sulfate, sulfated mannosyl glucosyl diether, mannosyl glucosyl diether, and disulfated mannosyl glucosyl diether. Based on the phenotypic, chemotaxonomic, phylogenetic, and phylogenomic properties, strains KK48T (= CGMCC 1.19060T = JCM 35607T), YCN56T (= CGMCC 1.62603T = JCM 36493T), SYNS191T (= CGMCC 1.62607T = JCM 36494T), and SYNS196T (= CGMCC 1.62608T = JCM 36495T) represent four novel species of the genera Salinibaculum and Salinirubellus. And Salinibaculum rarum sp. nov., Salinibaculum salinum sp. nov., Salinibaculum marinum sp. nov., and Salinirubellus litoreus sp. nov. are proposed to accommodate these strains.

Halophilic aminopeptidases with broad substrate specificity represent valuable biocatalysts for promoting protein hydrolysis in high-salt fermented foods. In this study, an M42 aminopeptidase from the halophilic archaeon, Haladaptatus litoreus, was identified and designated as APHap. The optimal reaction conditions for APHap were 2-2.5 M NaCl, a temperature of 60°C, and a pH of 7.5. It displayed robust activity and stability across a wide range of salinity, temperature, and pH conditions. APHap demonstrated exceptional tolerance to both organic solvents and surfactants. In contrast to most characterized M42 aminopeptidases, APHap exhibited a broad substrate spectrum, with the highest activity observed when using Leu-p-nitroaniline as the substrate. The Vmax and Km for APHap were 5.28 µmol/min/mg and 0.59 mM, respectively. When applied for fish protein hydrolysis in hypersaline conditions, APHap significantly increased the total free amino acid content, particularly enhancing the proportion of sweet and umami amino acids. To our knowledge, APHap is the first halophilic and mesophilic M42 aminopeptidase characterized from the genus Haladaptus. These desirable properties indicated that APHap has great potential for enhancing protein hydrolysis during the processing of high-salt fermented foods. PRACTICAL APPLICATION: The characteristics of APHap conform with the demands of high-salt fermented food production, highlighting its potential as a biocatalyst for improving both process efficiency and product quality.

Two novel halophilic archaeal strains (XZGYJ-43 T and ZJ1 T ) were isolated from Mangkang ancient solar saltern (Tibet, PR China) and Zhujiang river inlet (Guangdong, PR China), respectively. The comparison of the 16S rRNA gene sequences revealed that strain XZGYJ-43 T is related to the current species of the family Halobacteriaceae (89.2–91.7% similarity) and strain ZJ1 T showed 94.7–98.3% similarity to the current species of the genus Haladaptatus . Phylogenetic analyses based on 16S rRNA genes, rpoB ′ genes and genomes indicated that strain XZGYJ-43 T is separate from the related genera, Halocalculus , Salarchaeum and Halarchaeum of the family Halobacteriaceae , and strain ZJ1 T tightly clusters with the current species of the genus Haladaptatus . The average nucleotide identity, digital DNA–DNA hybridization and average amino acid identity values between strain XZGYJ-43 T and the current species of the family Halobacteriaceae were 71–75, 20–25 and 59–68 %, and these values between strain ZJ1 T and the current species of the genus Haladaptatus were 77–81, 27–32 and 76–82 %, respectively, clearly below the thresholds for prokaryotic species demarcation. These two strains could be distinguished from their relatives according to differential phenotypic characteristics. The major polar lipids of strain XZGYJ-43 T were phosphatidic acid (PA), phosphatidylglycerol (PG), phosphatidylglycerol phosphate methyl ester (PGP-Me), mannosyl glucosyl diether (DGD-1; DGD-PA) and sulphated mannosyl glucosyl diether (S-DGD-1; S-DGD-PA), and those of strain ZJ1 T were PA, PG, PGP-Me, DGD-PA, S-DGD-1 (S-DGD-PA) and sulphated galactosyl mannosyl glucosyl diether. Based on phenotypic, phylogenetic and genomic data, strain XZGYJ-43 T (=CGMCC 1.13890 T =JCM 33735 T ) represents a novel species of a new genus within the family Halobacteriaceae , and strain ZJ1 T (=CGMCC 1.18785 T =JCM 34917 T ) represents a novel species of the genus Haladaptatus , for which the names Halospeciosus flavus gen. nov., sp. nov. and Haladaptatus caseinilyticus sp. nov. are proposed, respectively.

Several groups of bacteria have complex life cycles involving cellular differentiation and multicellular structures. For example, actinobacteria of the genus Streptomyces form multicellular vegetative hyphae, aerial hyphae, and spores. However, similar life cycles have not yet been described for archaea. Here, we show that several haloarchaea of the family Halobacteriaceae display a life cycle resembling that of Streptomyces bacteria. Strain YIM 93972 (isolated from a salt marsh) undergoes cellular differentiation into mycelia and spores. Other closely related strains are also able to form mycelia, and comparative genomic analyses point to gene signatures (apparent gain or loss of certain genes) that are shared by members of this clade within the Halobacteriaceae. Genomic, transcriptomic and proteomic analyses of non-differentiating mutants suggest that a Cdc48-family ATPase might be involved in cellular differentiation in strain YIM 93972. Additionally, a gene encoding a putative oligopeptide transporter from YIM 93972 can restore the ability to form hyphae in a Streptomyces coelicolor mutant that carries a deletion in a homologous gene cluster (bldKA-bldKE), suggesting functional equivalence. We propose strain YIM 93972 as representative of a new species in a new genus within the family Halobacteriaceae, for which the name Actinoarchaeum halophilum gen. nov., sp. nov. is herewith proposed. Our demonstration of a complex life cycle in a group of haloarchaea adds a new dimension to our understanding of the biological diversity and environmental adaptation of archaea.

'Haloarcula aidinensis' was described by a pioneer Chinese scientist focused on halophilic archaea thirty years ago, and the type strain of 'Haloarcula aidinensis' was recently classified based on phylogenetic, phylogenomic, and comparative genomic analyses. Other three novel halophilic archaeal strains, CK38T, DT43T, and SYNS111T, isolated from diverse saline environments in China, were simultaneously subjected to polyphasic classification. 'Haloarcula aidinensis' A5 was found to be related to Haloarcula amylolytica, while strains CK38T, DT43T, and SYNS111T represented three novel species of Haloarcula based on phylogenetic, phylogenomic, and comparative genomic analyses. These strains can be distinguished from other species within the genus Haloarcula based on multiple phenotypic characteristics. The major phospholipids, phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, and phosphatidylglycerol sulfate can be detected in these strains, while the glycolipid profiles of these strains are diverse. Strains A5 and DT43T contained glucosyl mannosyl glucosyl diether and a diglycosyl diether, while other strains CK38T and SYNS111T had sulfated mannosyl glucosyl diether and mannosyl glucosyl diether. Thus, strain A5 should be a reference strain of Har. amylolytica and three novel species of Haloarcula, Haloarcula sediminis sp. nov., Haloarcula brevis sp. nov., and Haloarcula regularis sp. nov. are proposed to accommodate strains CK38T (= CGMCC 1.62732T = JCM 36675T), DT43T (= CGMCC 1.18924T = JCM 36146T), and SYNS111T (= CGMCC 1.62601T = JCM 36149T).

Four novel halophilic archaeal strains CGA53T, CG83T, FCH27T, and SEDH24 were isolated from a soda lake and two saline lakes in China, respectively. Strain CGA53T showed the highest 16S rRNA gene similarity (92.6%) to Salinilacihabitans rarus AD-4T, and the other three strains were found to be related to Halalkalicoccus species with similarities of 97.6-98.3%. Metagenomic studies indicated that these four strains are low abundant inhabitants detected in these hypersaline environments, and only one MAG of Chagannuoer Soda Lake (CG) could be assigned to the genus Halalkalicoccus. Their growth occurred at 20-60 °C (optima, 42, 37, 37-42, and 35 °C), 0.9-5.1 M NaCl (optima, 3.9, 2.6, 3.5, and 3 M), and 0-1.0 M MgCl2 (optima, 0.5, 0.7, and 0.1) and pH 5.5-10.5 (optima, 9.0, 7.5, 7.0, and 7.0), respectively. Phylogenetic and phylogenomic analyses revealed that strains CG83T, FCH27T, and SEDH24 cluster with the current species of the genus Halalkalicoccus, and strain CGA53T forms an independent branch separated from this genus. The average nucleotide identity (ANI), digital DNA-DNA hybridization (dDDH), and average amino acid identity (AAI) values among strains CGA53T, CG83T, FCH27T, SEDH24, and the type species of the current genera within the class Halobacteria were 67.4-81.6%, 16.5-28.6% and 49.7-74.1%, respectively, clearly lower than the cutoff values for species demarcation. Strain CGA53T may represent a novel species of a new genus according to the cutoff value for genus demarcation of 65% AAI. Diverse differential phenotypic characteristics, such as nutrition, biochemical activities, antibiotic sensitivity, and H2S formation, were found among these four strains and Halalkalicoccus species. Genome-based classification supported that strains CGA53T, CG83T, FCH27T, SEDH24, and the current species of Halalkalicoccus represent a novel family of the order Halobacteriales within the class Halobacteria.

Histamine, found abundantly in salt-fermented foods, poses a risk of food poisoning. Natronobeatus ordinarius, a halophilic archaeon isolated from a salt lake, displayed a strong histamine degradation ability. Its histamine oxidase (HOD) gene was identified (hod(Nbs)). This is the first report of an archaeal HOD. The HODNbs protein was determined to be a tetramer with a molecular weight of 307 kDa. HODNbs displayed optimum activity at 60-65 degrees C, 1.5-2.0 M NaCl, and pH 6.5. Notably, within the broad NaCl range between 0.5 and 2.5 M, HODNbs retained above 50% of its maximum activity. HODNbs exhibited good thermal stability, pH stability, and salinity tolerance. HODNbs was able to degrade various biogenic amines. The V-max of HODNbs for histamine was 0.29 mu mol/min/mg, and the K-m was 0.56 mM. HODNbs exhibited high efficiency in histamine removal from fish sauce, namely, 100 mu g of HODNbs degraded 5.63 mg of histamine (37.9%) in 10 g of fish sauce within 24 h at 50 degrees C. This study showed that HODNbs with excellent enzymatic properties has promising application potentials to degrade histamine in high-salt foods.

Two extremely halophilic archaeal strains, GSLN9 T and XZYJT29 T , were isolated from the saline soil in different regions of western China. Both strains GSLN9 T and XZYJT29 T have two 16S rRNA genes with similarities of 95.1 and 94.8 %, respectively. Strain GSLN9 T was mostly related to the genus Halomicrococcus based on 16S rRNA (showing 91.0–96.0 % identities) and rpoB′ genes (showing 92.0 % identity). Strain XZYJT29 T showed 92.1–97.6 % (16S rRNA gene) and 91.4–93.1 % ( rpoB′ gene) sequence similarities to its relatives in the genus Halosimplex , respectively. The polar lipid profile of strain GSLN9 T included phosphatidic acid (PA), phosphatidylglycerol (PG), phosphatidylglycerol phosphate methyl ester (PGP-Me), phosphatidylglycerol sulphate (PGS), sulphated mannosyl glucosyl diether (S-DGD-1) and sulphated galactosyl mannosyl glucosyl diether (S-TGD-1), mostly similar to that of Halomicrococcus hydrotolerans H22 T . PA, PG, PGP-Me, S-DGD-1 (S-DGD-PA), S 2 -DGD, S-TGD-1 and an unidentified glycolipid were detected in strain XZYJT29 T ; this polar lipid composition is similar to those of members of the genus Halosimplex . The average nucleotide identity, digital DNA–DNA hybridization and average amino acid identity values between these two strains and their relatives of the genera Halomicrococcus and Halosimplex were no more than 82, 27 and 80 %, respectively, much lower than the thresholds for species demarcation. Other phenotypic characterization results indicated that strains GSLN9 T and XZYJT29 T can be differentiated from the current species of the genera Halomicrococcus and Halosimplex , respectively. These results revealed that strains GSLN9 T (=CGMCC 1.15215 T =JCM 30842 T ) and XZYJT29 T (=CGMCC 1.15828 T =JCM 31853 T ) represent novel species of Halomicrococcus and Halosimplex , for which the names Halomicrococcus gelatinilyticus sp. nov. and Halosimplex aquaticum sp. nov. are proposed.

Halophilic archaea of the class Halobacteria are the most salt- requiring prokaryotes within the domain Archaea. In 1997, minimal standards for the description of new taxa in the order Halobacteriales were proposed. From then on, the taxonomy of the class Halobacteria provides an excellent example of how changing concepts on prokaryote taxonomy and the development of new methods were implemented. The last decades have witnessed a rapid expansion of the number of described taxa within the class Halobacteria coinciding with the era of genome sequencing development. The current members of the International Committee on Systematics of Prokaryotes Subcommittee on the Taxonomy of Halobacteria propose these revisions to the recommended minimal standards and encourage the use of advanced technologies in the taxonomic description of members of the Halobacteria. Most previously required and some recommended minimal standards for the description of new taxa in the class Halobacteria were retained in the present revision, but changes have been proposed in line with the new methodologies. In addition to the 16S rRNA gene, the rpoB ' gene is an important molecular marker for the identification of members of the Halobacteria. Phylogenomic analysis based on concatenated conserved, single- copy marker genes is required to infer the taxonomic status of new taxa. The overall genome relatedness indexes have proven to be determinative in the classification of the taxa within the class Halobacteria. Average nucleotide identity, digital DNA-DNA hybridization, and average amino acid identity values should be calculated for rigorous comparison among close relatives.