Phenotypic and genomic characterization of Bathyarchaeum tardum gen. nov., sp. nov., a cultivated representative of the archaeal class Bathyarchaeia .

are widespread in various anoxic ecosystems and are considered one of the most abundant microbial groups on the earth. There are only a few reports of laboratory cultivation of , and none of the representatives of this class has been isolated in pure culture. Here, we report a sustainable cultivation of the archaeon (strain M17C) enriched from anaerobic sediment of a coastal lake. The cells of strain M17C were small non-motile cocci, 0.4-0.7 μm in diameter. The cytoplasmic membrane was surrounded by an S-layer and covered with an outermost electron-dense sheath. Strain M17C is strictly anaerobic mesophile. It grows at 10-45°C (optimum 37°C), at pH 6.0-10.0 (optimum 8.0), and at NaCl concentrations of 0-60 g l (optimum 20 g l). Growth occurred in the presence of methoxylated aromatic compounds (3,4-dimethoxybenzoate and vanillate) together with complex proteinaceous substrates. Dimethyl sulfoxide and nitrate stimulated growth. The phylogenomic analysis placed strain M17C to BIN-L-1 genus-level lineage from the BA1 family-level lineage and B26-1 order-level lineage (former subgroup-8) within the class . The complete genome of strain M17C had a size of 2.15 Mb with a DNA G + C content of 38.1%. Based on phylogenomic position and phenotypic and genomic properties, we propose to assign strain M17C to a new species of a novel genus gen. nov., sp. nov. within the class . This is the first sustainably cultivated representative of . We propose under SeqCode the complete genome sequence of strain M17C (CP122380) as a nomenclatural type of , which should be considered as a type for the genus , which is proposed as a type for the family , order , and of the class .