A mesophilic, chemolithoautotrophic, neutrophilic and aerobic ammonia-oxidizing archaeon, designated strain MY1^T, was isolated from agricultural soil. Microscopic observation revealed short, rod-shaped cells with a diameter of 0.3-0.5 µm and length of 0.6-1.0 µm. The isolate had no flagella and pili, and possessed no genes associated with archaeal flagella synthesis. The major membrane lipids consisted mainly of the glycerol dibiphytanyl glycerol tetraether (GDGT) lipids GDGT-0 to GDGT-4 and crenarchaeol. The major intact polar lipids (IPLs) were determined as hexose plus phosphohexose IPL and dihexose IPL. Strain MY1^T obtains energy by aerobically oxidizing ammonia and carbon by fixing CO2. An optimal growth was observed at 25 °C, at pH 7 and with 0.2-0.4 % (w/v) salinity that corresponds with its terrestrial habitat. The addition of α-keto acids was necessary to stimulate growth. The strain tolerated ammonium and nitrite concentrations up to 10 and 5 mM, respectively. The MY1^T genome has a DNA G+C content of 32.7 mol%. Phylogenetic analysis based on the 16S rRNA gene showed that strain MY1^T belongs to the family Nitrosopumilaceaeof the phylum Thaumarchaeota, sharing the highest 16S rRNA gene sequence similarity (96.6-97.1 %) with marine isolates of the genus Nitrosopumilus. The average nucleotide identity was 78 % between strain MY1^T and Nitrosopumilus maritimus SCM1^T, indicating distant relatedness. Based on the phenotypic, phylogenetic and genomic analyses, it was concluded that strain MY1^T belongs to the novel genus Nitrosarchaeum, under which the name Nitrosarchaeum koreense sp. nov. is proposed as the type species. The type strain is MY1^T (=JCM 31640^T=KCTC 4249^T).

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