Two extremely halophilic archaea, strains RO2-11^T and HO2-1, were isolated from two Chinese marine solar salterns, Rudong solar saltern and Haimen solar saltern, respectively. Cells of the two strains were polymorphic and Gram-stain-negative; colonies were red-pigmented. The two strains grew at NaCl concentrations of 2.6–4.3 M (optimum 3.9 M) and required at least 0.1 M Mg²⁺ for growth. They were able to grow over a pH range of 6.0–8.0 and a temperature range of 20–50 °C, with optimal pH of 7.5 and optimal temperature of 37 °C. The major polar lipids of strain RO2-11^T and strain HO2-1 were phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester and three glycolipids, two of them chromatographically identical to S-DGD-1 and DGD-1, the third unidentified. The 16S rRNA gene sequence similarity of strain RO2-11^T and strain HO2-1 was 99.3 % and highest sequence similarity with the closest relative (Haloferax larsenii) was 91.4 %. Based on the data obtained, the two isolates could not be classified in any recognized genus of the family Halobacteriaceae. Strain RO2-11^T and strain HO2-1 are thus considered to represent a novel species of a new genus within the family Halobacteriaceae, for which the name Halogranum rubrum gen. nov., sp. nov. is proposed. The type strain is RO2-11^T (=CGMCC 1.7738^T =JCM 15772^T).

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.

Three rod-shaped halophilic archaeal strains, DL-M4^T, LYG-109 and DLLS-108^T, were isolated from the salted brown alga Laminaria produced in different marine areas of PR China. Cells of strains were motile, formed red-pigmented colonies on agar and lysed in distilled water. The three strains grew optimally with 2.6 M NaCl, with 0.05–0.3 M MgCl₂, at 37 °C and at pH 7.0–7.5. The results of phylogenetic analyses based on the 16S rRNA and rpoB′ genes differentiated these strains into two clusters belonging to the genus Halostella , which currently contains Halostella salina CBA1114^T and Halostella limicola LT12^T. Strains DL-M4^T and LYG-109 formed a single cluster separate from the current two members of Halostella (94.4–95.7 and 90.0–90.9 % similarities, respectively) while strain DLLS-108^T had Hsl. salina CBA1114^T as its nearest neighbour (97.7–97.8 and 95.9 % similarities, respectively) and was separated from Hsl. limicola LT12^T (94.4–95.8 and 93.4 % similarities, respectively). These clusters represented two distinct novel species as indicated by phenotypic characteristics, polar lipid compositions and whole-genome comparisons. Diverse phenotypic characteristics, morphology and growth characteristics, nutrition and miscellaneous biochemical tests differentiate strains DL-M4^T, LYG-109, DLLS-108^T from Hsl. limicola LT12^T and Hsl. salina CBA1114^T. Strains DL-M4^T and LYG-109 contained phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester and three unidentified glycolipids, while strain DLLS-108^T contained these polar lipids and two unidentified phospholipids. The major respiratory quinones detected in the three isolates were menaquinone MK-8 and MK-8(H₂). The average nucleotide identity (ANI) and in silico DNA–DNA hybridization (isDDH) values between the isolated strains and the current two members of Halostella were found to be 79.3–86.6 (ANI) and 22.9–49.8 % (isDDH). All these results showed that the three isolates represent two novel species of the genus Halostella for which the names Halostella pelagica sp. nov. [type strain dl-M4^T (=CGMCC 1.13603^T=JCM 32954^T)] and Halostella litorea sp. nov. [type strain DLLS-108^T(=CGMCC 1.13610^T=JCM 32955^T)] are proposed.