Natronorubrum halophilum sp. nov. isolated from two inland salt lakes

Two halophilic archaeal strains, SHR37^T and NEN6, were isolated from salt lakes located in the Tibet and Xinjiang regions of China. The two strains were found to form a single cluster (99.9% and 99.3% similarity, respectively) separating them from the six current members of Natronorubrum (94.7-96.9% and 86.1-90.8% similarity, respectively) on the basis of the 16S rRNA and rpoB' gene sequence similarities and phylogenetic analysis. Diverse phenotypic characteristics differentiate strains SHR37^T and NEN6 from current Natronorubrum members. Their polar lipids are C₂₀C₂₀ and C₂₀C₂₅glycerol diether derivatives of PG, PGP-Me, and a major gycolipid chromatographically identical to disulfated mannosyl glucosyl diether (S₂-DGD). Four minor unidentified gycolipids are also present. The OrthoANI and in silico DDH values of the two strains were 97.3% and 76.1%, respectively, which were much higher than the threshold values proposed as a species boundary (ANI 95-96% and in silico DDH 70%), which revealed that the two strains represent one species; the two values (ANI 79.0-81.9% and in silico DDH 23.5-25.7%) of the strains examined in this study and the current members of Natronorubrum are much lower than the recommended threshold values, suggesting that strains SHR37^T and NEN6 represent a genomically different species of Natronorubrum. These results showed that strains SHR37^T (= CGMCC 1.15233^T = JCM 30845^T) and NEN6 (= CGMCC 1.17161) represent a novel species of Natronorubrum, for which the name Natronorubrum halophilum sp. nov. is proposed.