Halopiger thermotolerans sp. nov., a thermo-tolerant haloarchaeon isolated from commercial salt.

Three thermo-tolerant halophilic archaeal strains, SR-441T, SR-412 and SR-188, were isolated from commercial salt samples. Cells were non-motile pleomorphic rod-shaped, and stained Gram-negative. Colonies were pink-pigmented. The three strains were able to grow with 1.7–4.6 M NaCl (optimum, 2.5 M), at pH 6.5–9.0 (optimum, pH 8.0) and at 35–60 °C (optimum, 45 °C). The orthologous 16S rRNA gene sequence similarities amongst the three strains were 98.8–99.3 %, and the level of DNA–DNA relatedness was 71–74 and 72–75 % (reciprocally). The closest relative was Halopiger aswanensis JCM 11628T with 98.6 %–99.1 % similarity in the orthologous 16S rRNA gene sequences, followed by two more Halopiger species, Halopiger xanaduensis JCM 14033T (98.5 %–99.1 %) and Halopiger salifodinae JCM 9578T (95.5 %–95.6 %). DNA–DNA relatednesses between the three strains and H. aswanensis JCM 11628T and H. xanaduensis JCM 14033T were 61 and 54 %, respectively. The polar lipids of the three novel strains were phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, and bis-sulfated diglycosyl archaeol-1. The most distinctive feature of the three strains was the ability to grow at 60 °C, while the maximum growth temperature of H. aswanensis is 55 °C. Based on phenotypic and phylogenetic analyses, the isolates are considered to represent a novel species of the genus Halopiger , for which the name Halopiger thermotolerans sp. nov. is proposed. The type strain is SR-441T (=JCM 19583T=KCTC 4248T) isolated from solar salt produced in Australia. SR-412 (=JCM 19582) and SR-188 (=JCM 19581) isolated from commercial salt samples are additional strains of the species.