Haloarchaea of the class Halobacteria (phylum Methanobacteriota) are a group of microorganisms that depend on high salt to sustain their growth and are mainly found in diverse salt environments such as salt lakes, soda lakes, salterns, and salt mines, and usually require at least 15 % (w/v) salt concentration for optimal growth (Göker and Oren, 2023, Oren, 2008). Haloarchaea do not contain peptidoglycan in their cell walls and exhibit diverse cell morphology (coccus, rod, triangular, square, filamentous, or polymorphic) (Burns et al., 2007, Guan et al., 2012, Minegishi et al., 2010, Wu et al., 2023). The class Halobacteria currently contains two orders, nine families, 77 genera, and 346 species (LPSN, https://lpsn.dsmz.de/class/halobacteria) (Cui et al., 2023). Among these nine families of the class Halobacteria, three of them accommodate more than 50 species, they are Haloferacaceae (124 species), Natrialbaceae (79 species), and Haloarculaceae (70 species). Contrary to those of the families Haloferacaceae and Haloarculaceae, most representatives of the family Natrialbaceae were first cultivated from salt lakes. The Qinghai-Xizang Plateau plays an important role in specific diversification (Ding et al., 2020). Different salt lakes are spread throughout this region and come into being a unique natural landscape (Zheng, 2011, Oren, 2008). In a previous investigation of halophilic archaeal diversity in the salt lakes on the Qinghai-Xizang Plateau, two halophilic archaeal strains (KZCA124 and TS33T) were successively isolated from two distant salt lakes in 2018 and 2020, respectively. These two strains closely related to each other and other species of the family Natrialbaceae based on the comparison of 16S rRNA and rpoB′ gene similarities.

The family Natrialbaceae was established in 2015 and currently contains 19 genera with validly published names (LPSN, https://lpsn.dsmz.de/family/natrialbaceae) (Gupta et al., 2015). The type genus of the family is Natrialba, and the type species Natrialba asiatica was described in 1995 based on strain 172P1T isolated from beach sands attached with granular salts in Japan (Masahiro et al., 1995). The strains of the family Natrialbaceae are mainly found in alkaline hypersaline environments and most of them prefer alkaline conditions for growth. The polar lipid profiles of the family Natrialbaceae were diverse, the neutrophilic representatives always contained phospholipids and glycolipids while the alkaliphilic representatives only had phospholipids (Oren et al., 2009). Their phospholipids were phosphatidic acid (PA), phosphatidylglycerol (PG), phosphatidylglycerol phosphate methyl ester (PGP-Me), and phosphatidylglycerol sulfate (PGS). Mannosylglucosyl diethyl ether sulfate (S2-DGD) was the common glycolipid detected in most neutrophilic representatives, then were mannosylglucosyl diethyl ether sulfate (S-DGD-1), mannosylglucosidyl diethyl ether (DGD-1), and sulfated galactosyl mannosyl glucosyl diether (S-TGD-1) (Li et al., 2023, Sun et al., 2022, Tan et al., 2023). In this study, strains TS33T and KZCA124 isolated from Tuosu Salt Lake (Qinghai) and Kunzhongcuo Salt Lake (Xizang) were subjected to a polyphasic taxonomic characterization, and their diversity among the originated salt lakes was evaluated by culture-independent approach.