Halomontanus rarus gen. nov., sp. nov., a novel halophilic archaeon of the family Natrialbaceae from salt lakes on the Qinghai-Xizang Plateau

Two halophilic archaeal strains TS33^T and KZCA124 were isolated from two distant salt lakes on the Qinghai-Xizang Plateau, respectively. Culture-independent analysis indicated that these two strains were original inhabitants but low abundant taxa in respective salt lakes. Strains TS33^T and KZCA124 were able to grow at 20–60 °C (optimum were 42 and 35 °C, respectively), with 0.9–4.8 M NaCl (optimum were 3.0 and 2.6 M, respectively), with 0–0.7 M MgCl₂ (optimum, 0.3 M) and at pH 5.0–9.5 (optimum were pH 7.5 and pH 7, respectively). The 16S rRNA and rpoB' gene similarities between these two strains were 99.7% and 99.4%, and these two similarities among strains TS33^T, KZCA124, and existing species of the family Natrialbaceae were 90.6–95.5% and 84.4–89.3%, respectively. Phylogenetic and phylogenomic analyses indicated that strains TS33^T and KZCA124 formed an independent branch separated from neighboring genera, Saliphagus, Natronosalvus, and Natronobiforma. The average nucleotide identity (ANI), digital DNA-DNA hybridization (dDDH), and average amino acid identity (AAI) values between strains TS33^T and KZCA124 were 96.4%, 73.1%, and 96.7%, respectively, higher than the thresholds for species demarcation. The overall genome-related indexes between these two strains and existing species of family Natrialbaceae were 73–77%, 21–25%, and 63–70%, respectively, significantly lower than the species boundary thresholds. Strains TS33^T and KZCA124 may represent a novel species of a new genus within the family Natrialbaceae judged by the cutoff value of AAI (≤76%) proposed to differentiate genera within the family Natrialbaceae. The major polar lipids of strains TS33^T and KZCA124 were phosphatidic acid, phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, sulfated mannosyl glucosyl diether, and sulfated galactosyl mannosyl glucosyl diether. These two strains could be distinguished from the related genera according to differential phenotypic characteristics. These phenotypic, phylogenetic, and genomic analyses revealed that strains TS33^T (=KCTC 4310^T = MCCC 4K00132^T) and KZCA124 (=CGMCC 1.17432 = JCM 34316) represent a novel species of a new genus of the family Natrialbaceae and were named Halomontanus rarus gen. nov., sp. nov.