Nitrosotalea devaniterrae gen. nov., sp. nov. and Nitrosotalea sinensis sp. nov., two acidophilic ammonia oxidising archaea isolated from acidic soil, and proposal of the new order Nitrosotaleales ord. nov. within the class Nitrososphaeria of the phylum Nitrososphaerota.

Two obligately acidophilic, mesophilic and aerobic soil ammonia-oxidising archaea were isolated from a pH 4.5 arable sandy loam (UK) and pH 4.7 acidic sulphate paddy soil (PR China) and designated strains Nd1^T and Nd2^T, respectively. The strains shared more than 99 % 16S rRNA gene sequence identity and their genomes were both less than 2 Mb in length, sharing 79 % average nucleotide identity, 81 % average amino acid identity and a DNA G+C content of approximately 37 mol%. Both strains were chemolithotrophs that fixed carbon dioxide and gained energy by oxidising ammonia to nitrite, with no evidence of mixotrophic growth. Neither strain was capable of using urea as a source of ammonia. Both strains were non-motile in culture, although Nd1^T does possess genes encoding flagella components and therefore may be motile under certain conditions. Cells of Nd1^T were small angular rods 0.5-1 µm in length and grew at pH 4.2-5.6 and at 20-30 °C. Cells of Nd1^T were small angular rods 0.5-1 µm in length and grew at pH 4.0-6.1 and at 20-42 °C. Nd1^T and Nd2^T are distinct with respect to genomic and physiological features and are assigned as the type strains for the species Nitrosotalea devaniterrae sp. nov. (type strain, Nd1^T=NCIMB 15248^T=DSM 110862^T) and Nitrosotalea sinensis sp. nov. (type strain, Nd2^T=NCIMB 15249^T=DSM 110863^T), respectively, within the genus Nitrosotalea gen. nov. The family Nitrosotaleaceae fam. nov. and order Nitrosotaleales ord. nov. are also proposed officially.