Halorubrum rubrum sp nov., an extremely halophilic archaeon from a Chinese salt lake

Two halophilic archaeal strains, YC87(T) and YCA11, were isolated from Yuncheng salt lake in Shanxi, China. Cells of the two strains were observed to be pleomorphic rod-shaped, stained Gram-negative and produced red-pigmented colonies. Strain YC87(T) was able to grow at 20-50 A degrees C (optimum 37 A degrees C), at 1.4-4.8 M NaCl (optimum 2.1 M NaCl), at 0.05-1.0 M MgCl2 (optimum 0.3 M MgCl2) and at pH 6.0-9.0 (optimum pH 7.0) while strain YCA11 was able to grow at 20-50 A degrees C (optimum 37 A degrees C), at 2.1-4.8 M NaCl (optimum 3.1 M NaCl), at 0.01-0.7 M MgCl2 (optimum 0.1 M MgCl2) and at pH 6.0-9.0 (optimum pH 7.5). The cells of both isolates were observed to lyse in distilled water. The minimum NaCl concentrations that prevented cell lysis were determined to be 8 % (w/v) for strain YC87(T) and 12 % (w/v) for strain YCA11. The major polar lipids of the two strains were identified as phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, phosphatidylglycerol sulfate and one major glycolipid chromatographically identical to sulfated mannosyl glucosyl diether; another major glycolipid and trace amounts of several unidentified lipids were also detected. The 16S rRNA gene sequences of the two strains were 99.8 % identical, showing 93.2-98.2 % similarity to members of the genus Halorubrum of the family Halobacteriaceae. The rpoB' gene similarity between strains YC87(T) and YCA11 was 99.3 % and showed 87.5-95.2 % similarity to the closest relative members of the genus Halorubrum. The DNA G+C content of strains YC87(T) and YCA11 were determined to be 64.9 and 64.5 mol%, respectively. The DNA-DNA hybridization value between strain YC20(T) and strain YC77 was 87 % and the two strains showed low DNA-DNA relatedness with Halorubrum cibi JCM 15757(T) and Halorubrum aquaticum CGMCC 1.6377(T), the most related members of the genus Halorubrum. The phenotypic, chemotaxonomic and phylogenetic properties suggest that strains YC87(T) and YCA11 represent a novel species of the genus Halorubrum, for which the name Halorubrum rubrum sp. nov. is proposed. The type strain is YC87(T) (=CGMCC 1.12124(T) = JCM 18365(T)).