Halorubrum salinarum sp. nov., an extremely halophilic archaeon isolated from a saturated brine pond of a saltern

Abstract

A novel extremely halophilic archaeon, strain RHB-C^T, was isolated from a saturated brine pond of a solar saltern in Bolinao, Pangasinan, Philippines. Colonies were orange-red-pigmented, smooth, convex and round on a solid modified growth medium containing 25 % (w/v) of total salts. Cells of strain RHB-C^T on the solid modified growth medium were ovoid-shaped (0.89-2.66 µm long), while the cells in a liquid modified growth medium were rod-shaped (1.53-5.65 µm long and 0.45-1.03 µm wide). The strain was Gram-stain-negative, motile and strictly aerobic. Strain RHB-C^T grew with NaCl concentrations ranging from 10 to 30 % (w/v; optimum, 20-25 %), at pH 6.5-8.5 (optimum, pH 7.0-7.5) and at 20-55 °C (optimum, 40-45 °C). Furthermore, the strain grew even in the absence of Mg²⁺; however, when supplemented with Mg²⁺, growth was observed optimally at 0.2-0.4 M Mg²⁺. The 16S rRNA gene phylogeny inferred that the strain is a member of the genus Halorubrum and was related to Halorubrum xinjiangense CGMCC 1.3527^T (99.0 %), Halorubrum sodomense DSM 3755^T (98.8 %), Halorubrum coriense Ch2^T (98.8 %), Halorubrum trapanicum NRC 34021^T (98.4 %) and Halorubrum distributum JCM 9100^T (98.1 %). The rpoB' gene sequences also showed that strain RHB-C^T is related to Hrr. xinjiangense JCM 12388^T (97.1 %), Hrr. distributum JCM 9100^T (97.1 %), Hrr. coriense JCM 9275^T (96.5 %), Hrr. californiense JCM 14715^T (96.5 %), Hrr. trapanicum JCM 10477^T (96.3%), Hrr. sodomense JCM 8880^T (96.2%) and Hrr. tebenquichense DSM 14210^T (95.6 %). The DNA G+C content of strain RHB-C^T was 68.7 mol% (genome). Digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values between strain RHB-C^T and the closely related species of Halorubrum were below 40 and 90 %, respectively, which are far below the thresholds to delineate a new species. The polar lipids of strain RHB-C^T were phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, phosphatidylglycerol sulphate and sulfated mannosyl glycosyl diether. Based on dDDH and ANI values, and the significant morphological and physiological differences from known taxa, it is hereby suggested that strain RHB-C^T represents a novel species of the genus Halorubrum, for which the name Halorubrum salinarum sp. nov. is proposed. The type strain is RHB-C^T (=KCTC 4274^T=CMS 2103^T).

Keywords: Haloarchaeon; polyphasic taxonomy; solar saltern.