Atrimonas thermophila gen. nov., sp. nov., a novel anaerobic thermophilic bacterium of the phylum Atribacterota isolated from deep subsurface gas field and proposal of Atrimonadaceae fam. nov. within the class Atribacteria in the phylum Atribacterota

A novel anaerobic, thermophilic bacterium of the class Atribacteria, strain M15^T, was isolated from a high-temperature gas reservoir, Japan. Cells of strain M15^T were gram-negative, short oval-shaped, and lacked flagella. Growth occurred at 45–75 °C (optimum 70–75 °C) and pH 6.5–8.5 (optimum pH 7.5–8.0) and was fast under optimal conditions (doubling time 11.4 h). Yeast extract was required for growth. Fermentative growth with glucose, arabinose, xylose, and cellobiose was observed. The major fermentative end products of glucose were acetate and hydrogen. The major cellular fatty acids were C_16:0, iso-C_15:0, and C_18:0. The genomic G + C content was 46.0 mol%. Fluorescence and electron microscopy observations revealed the intracellular localization of genomic DNA surrounded by a membrane in the cells of strain M15^T as reported in a sole validly described species of the class Atribacteria in the phylum Atribacterota, Atribacter laminatus strain RT761^T, suggesting that the unique morphological traits are widely shared in this class. Phylogenetic analyses indicated that strain M15^T belongs to a distinct family-level lineage in the class Atribacteria and shows low similarities to Atribacter laminatus strain RT761^T (16S rRNA gene sequence identity of 90.1 %, average nucleotide identity [ANI] of 66.1 %, average amino acid identity [AAI] of 55.8 %). Phenotypic traits of strain M15^T (thermophilic, fast-growing, relatively high G + C content, etc.) were clearly distinct from A. laminatus. Based on these phenotypic and genomic properties, we propose a novel genus and species, Atrimonas thermophila gen. nov., sp. nov. for strain M15^T (=JCM39389^T, =KCTC25731^T) representing a novel family Atrimonadaceae fam., nov. in the class Atribacteria.