Haloplanus litoreus sp. nov. and Haloplanus ruber sp. nov., from a marine solar saltern and an aquaculture farm, respectively

Abstract

Two halophilic archaea, strains GX21^T and R35^T, were isolated from a marine solar saltern and an aquaculture farm in China, respectively. Cells of the two strains were observed to be pleomorphic, flat, to contain gas vesicles, stain Gram-negative and produce red-pigmented colonies. Strain GX21^T was found to be able to grow at 25–50 °C (optimum 37 °C), at 2.6–4.8 M NaCl (optimum 3.4 M NaCl), at 0.05–1.0 M MgCl₂ (optimum 0.1 M MgCl₂) and at pH 6.0–8.5 (optimum pH 6.5) while strain R35^T was found to be able to grow at 25–45 °C (optimum 37 °C), at 2.1–4.8 M NaCl (optimum 3.1 M NaCl), at 0–0.7 M MgCl₂ (optimum 0.03 M MgCl₂) and at pH 5.5–9.5 (optimum pH 6.5–7.0). The cells of both isolates were observed to lyse in distilled water. The minimum NaCl concentrations that prevented cell lysis were determined to be 15 % (w/v) for strain GX21^T and 12 % (w/v) for strain R35^T. The major polar lipids of the two strains were identified as phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, phosphatidylglycerol sulfate, one major glycolipid and a minor lipid chromatographically identical to sulfated mannosyl glucosyl diether and mannosyl glucosyl diether, respectively. 16S rRNA gene sequence analysis revealed that strains GX21^T and R35^T show 97.1 % sequence similarity to each other and are closely related to Haloplanus aerogenes TBN37^T (96.8 and 95.8 %), Haloplanus vescus RO5-8^T (96.7 and 96.1 %), Haloplanus salinus YGH66^T (96.4 and 95.8 %) and Haloplanus natans JCM 14081^T (96.3 and 95.4 %). The rpoB′ gene similarity between strains GX21^T and R35^T is 90.5 % and show 88.5–90.8 % similarity to the Haloplanus species with validly published names. The DNA G+C content of strain GX21^T and R35^T were determined to be 65.8 and 66.0 mol%, respectively. The DNA–DNA hybridization values between strain GX21^T and strain R35^T, and the two strains with the Haloplanus species with validly published names, showed less than 50 % DNA–DNA relatedness. It was concluded that strain GX21^T (=CGMCC 1.10456^T = JCM 17092^T) and strain R35^T (=CGMCC 1.10594 ^T = JCM 17271^T) represent two new species of Haloplanus, for which the names Haloplanus litoreus sp. nov. and Haloplanus ruber sp. nov. are proposed.