Halorubrum aquaticum sp. nov., an archaeon isolated from hypersaline lakes

Two halophilic archaea, strains EN-2(T) and SH-4, were isolated from the saline lakes Erliannor and Shangmatala, respectively, in Inner Mongolia, China. Cells were strictly aerobic, motile rods. Colonies were red. Strains EN-2(T) and SH-4 were able to grow at 25-50 °C (optimum 35-40 °C), with 2.5-5.0 M NaCl (optimum 3.4 M NaCl) and at pH 6.0-9.0 (optimum pH 7.5). MgCl(2) was not required for growth. Cells lysed in distilled water and the lowest NaCl concentration that prevented cell lysis was 12 % (w/v). On the basis of 16S rRNA gene sequence analysis, strains EN-2(T) and SH-4 were closely related to Halorubrum cibi B31(T) (97.9 and 98.0 % similarity, respectively), Hrr. tibetense 8W8(T) (97.3 and 97.7 %), Hrr. alkaliphilum DZ-1(T) (96.8 and 97.1 %), Hrr. luteum CGSA15(T) (96.8 and 97.0 %) and Hrr. lipolyticum 9-3(T) (96.8 and 97.0 %). DNA-DNA hybridization showed that strains EN-2(T) and SH-4 did not belong to the same species as any of these strains (≤ 45 % DNA-DNA relatedness) but that they are members of the same species (>70 % DNA-DNA relatedness). Polar lipid analysis revealed that strains EN-2(T) and SH-4 contained phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, sulfated diglycosyl diethers and several unidentified glycolipids. The DNA G+C content of both isolates was 62.1 mol%. It was concluded that strains EN-2(T) and SH-4 represent a novel species of the genus Halorubrum, for which the name Halorubrum aquaticum sp. nov. is proposed. The type strain is EN-2(T) ( = CECT 7174(T)  = CGMCC 1.6377(T)  = JCM 14031(T)).