| Abstract |
Two halophilic moderately acidophilic archaeal strains, MH1-136-2(T) and MH1-370-1 were isolated from commercial salt samples made from seawater in Japan and Indonesia, respectively. Cells of the two strains were pleomorphic and Gram-stain-negative. Strain MH1-136-2(T) was pink pigmented, while MH1-370-1 was orange-red pigmented. Strain MH1-136-2(T) was able to grow at 9-30 % (w/v) NaCl (with optimum, 21 % NaCl, w/v) at pH 4.5-6.2 (optimum, pH 5.2-5.5) and at 18-55 °C (optimum, 45 °C). Strain MH1-370-1 was able to grow at 12-30 % (w/v) NaCl (optimum, 18 %, w/v) at pH 4.2-6.0 (optimum, pH 5.2-5.5) and 20-50 °C (optimum, 45 °C). Strain MH1-136-2(T) required at least 1 mM Mg(2+), while MH1-370-1 required at least 10 mM for growth. Both strains reduced nitrate and nitrite under aerobic conditions. The 16S rRNA gene sequences of strains MH1-136-2(T) and MH1-370-1 were identical, and the closest relative was Halarchaeum rubridurum MH1-16-3(T) with 98.3 % similarity. The level of DNA-DNA relatedness between these strains was 90.9 % and 92.4 % (reciprocally), while that between MH1-136-2(T) and Halarchaeum acidiphilum MH1-52-1(T), Halarchaeum salinum MH1-34-1(T) and Halarchaeum rubridurum MH1-16-3(T) was 37.7 %, 44.3 % and 41.1 % (each an average), respectively. Based on the phenotypic, genotypic and phylogenetic analyses, it is proposed that the isolates represent a novel species of the genus Halarchaeum, for which the name Halarchaeum nitratireducens sp. nov. is proposed. The type strain is MH1-136-2(T) ( = JCM 16331(T) = CECT 7573(T)) isolated from solar salt produced in Japan.
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