Aristaeella hokkaidonensis gen. nov. sp. nov. and Aristaeella lactis sp. nov., two rumen bacterial species of a novel proposed family, Aristaeellaceae fam. nov.

Two strains of Gram- negative, anaerobic, rod- shaped bacteria, from an abundant but uncharacterized rumen bacterial group of the order 'Christensenellales', were phylogenetically and phenotypically characterized. These strains, designated R- 7T and WTE2008T, shared 98.6-99.0 % sequence identity between their 16S rRNA gene sequences. R- 7T and WTE2008T clustered together on a distinct branch from other Christensenellaceae strains and had <88.1 % sequence identity to the closest typestrain sequence from Luoshenia tenuis NSJ-44T. The genome sequences of R- 7T and WTE2008T had 83.6 % average nucleotide identity to each other, and taxonomic assignment using the Genome Taxonomy Database indicates these are separate species within a novel family of the order 'Christensenellales'. Cells of R- 7T and WTE2008T lacked any obvious appendages and their cell wall ultra- structures were characteristic of Gram- negative bacteria. The five most abundant cellular fatty acids of both strains were C16:0, C16: 0 iso, C17: 0 anteiso, C18: 0 and C15: 0 anteiso. The strains used a wide range of the 23 soluble carbon sources tested, and grew best on cellobiose, but not on sugar- alcohols. Xylan and pectin were fermented by both strains, but not cellulose. Acetate, hydrogen, ethanol and lactate were the major fermentation end products. R- 7T produced considerably more hydrogen than WTE2008T, which produced more lactate. Based on these analyses, Aristaeellaceae fam. nov. and Aristaeella gen. nov., with type species Aristaeella hokkaidonensis sp. nov., are proposed. Strains R- 7T (=DSM 112795T=JCM 34733T) and WTE2008T (=DSM 112788T=JCM 34734T) are the proposed type strains for Aristaeella hokkaidonensis sp. nov. and Aristaeella lactis sp. nov., respectively.