Salinadaptatus halalkaliphilus gen. nov., sp. nov., a haloalkaliphilic archaeon isolated from salt pond in Inner Mongolia Autonomous Region, China

Salinilacihabitans rarus gen. nov., sp. nov., Natrononativus amylolyticus gen. nov., sp. nov., Natronobeatus ordinarius gen. nov., sp. nov., and Halovivax gelatinilyticus sp. nov., halophilic archaea, isolated from a salt lake and soda lakes

Four halophilic archaea strains, AD-4^T, CGA30^T, CGA73^T, and WLHSJ27^T, were isolated from a salt lake and two soda lakes located in different regions of China. The 16S rRNA and rpoB' gene sequence similarities among strains AD-4^T, CGA30^T, CGA73^T, WLHSJ27^T, and the current species of the family Natrialbaceae were 90.9-97.5% and 83.1-91.8%, respectively. The phylogenetic and phylogenomic analyses revealed that these four strains separated from existing genera in the family Natrialbaceae and formed distant branches. The ANI, isDDH, and AAI values among these four strains and the current members of the family Natrialbaceae were 72-79%, 20-25%, and 63-73%, respectively, much lower than the threshold values for species demarcation. Strains AD-4^T, CGA73^T, and WLHSJ27^T may represent three novel genera of the family Natrialbaceae according to the cutoff value of AAI (≤ 76%) proposed to differentiate genera within the family Natrialbaceae. These four strains could be distinguished from the related genera according to differential phenotypic characteristics. The major phospholipids of these four strains were identical while their glycolipid profiles were diverse. DGD-1 is a major glycolipid found in strain AD-4^T, trace glycolipids, DGD-1, and S-DGD-1, and (or) S-TGD-1 was found in the other three strains. The major respiratory quinones detected in the four strains were menaquinone MK-8 and MK-8(H₂). This polyphasic classification indicated that strains AD-4^T, CGA73^T, and WLHSJ27^T represent three novel species of three new genera with the family Natrialbaceae, and strain CGA30^T represents a novel species of Halovivax.

Genome-based classification of the class Halobacteria and description of Haladaptataceae fam. nov. and Halorubellaceae fam. nov

Currently, there are four mainstream taxonomic opinions on the classification of the class Halobacteria at the family and order levels. The International Committee on Systematics of Prokaryotes Subcommittee on the Taxonomy of Halobacteria (ICSP), List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Centre for Biotechnology Information (NCBI) adopted taxonomies have three to four orders and up to eight families, while the Genome Taxonomy Database (GTDB) taxonomy proposes only one order with nine families. To resolve the taxonomic inconsistency, phylogenomic analyses based on concatenated single-copy orthologous proteins and 122 concatenated conserved single-copy marker proteins were conducted to infer the taxonomic status of the current representatives of the class Halobacteria at the family and order levels. The current 76 genera with validly published names of the class Halobacteria were able to be assigned into eight families in one order. On the basis of these results, it is proposed that the current species with validly published names of the class Halobacteria should be remerged into the order Halobacteriales, then assigned to eight families, Haladaptataceae, Haloarculaceae, Halobacteriaceae, Halococcaceae, Haloferacaceae, Natronoarchaeaceae, Natrialbaceae and Halorubellaceae. Thus, Haladaptataceae fam. nov. is described based on Haladaptatus, Halomicrococcus and Halorussus and Halorubellaceae fam. nov. is proposed incorporating Haloarchaeobius and Halorubellus, respectively.

Description of Halosolutus amylolyticus gen. nov., sp. nov., Halosolutus halophilus sp. nov. and Halosolutus gelatinilyticus sp. nov., and genome-based taxonomy of genera Natribaculum and Halovarius

Three extremely halophilic archaeal strains (LT55T, SQT-29-1T and WLHS5T) were isolated from Gobi saline soil and a salt lake, China. These strains were most related to the genera Natribaculum and Halovarius (92.6–95.1 % similarities), and showed low similarities with other genera within the family Natrialbaceae based on 16S rRNA genes. Phylogenomic analysis confirmed that the three strains formed a distinct clade separated from the related genera Halostagnicola and Natronococcus , which indicated that they may represent a novel genus of the family Natrialbaceae . The average nucleotide identity (ANI), in silico DNA–DNA hybridization (isDDH) and average amino acid identity (AAI) values among the three strains were no more than 87, 34 and 85 %, respectively, much lower than the threshold values for species demarcation. The major phospholipids of the three strains were phosphatidic acid (PA), phosphatidylglycerol (PG) and phosphatidylglycerol phosphate methyl ester (PGP-Me). The glycolipid profiles of the three strains were diverse; sulfated mannosyl glucosyl diether (S-DGD-1) and disulfated mannosyl glucosyl diether (S2-DGD) were found in strains LT55T and WLHS5T, while mannosyl glucosyl diether (DGD-1) and S-DGD-1 in strain SQT-29-1T. The combination of phenotypic, chemotaxonomic, phylogenetic and genomic analyses suggested that strains WLHS5T (=CGMCC 1.13781T = JCM 33558T), SQT-29-1T (=CGMCC 1.16065T = JCM 33554T) and LT55T (=CGMCC 1.15188T = JCM 30838T) represent three novel species of a new genus within the family Natrialbaceae , for which the names, Halosolutus amylolyticus gen. nov., sp. nov., Halosolutus gelatinilyticus sp. nov. and Halosolutus halophilus sp. nov., are proposed. Genome-based classification of genera Natribaculum and Halovarius revealed that Halovarius luteus should be transferred to the genus Natribaculum as Natribaculum luteum comb. nov. and Natribaculum longum as a heterotypic synonym of Natribaculum breve Liu et al. 2015.