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 C(20)C(25)glycerol diether derivatives of PG, PGP-Me, and a major gycolipid chromatographically identical to disulfated mannosyl glucosyl diether (S-2-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.