Members of the class are little studied, important fastidious anaerobes within the human gut microbiota. is a core member of the gut microbiota that can present several different fermentation profiles within individuals, while is implicated in xenobiotic metabolism. Recent ‘culturomics’ studies have greatly increased the number of recovered from human-associated samples, with the names of nine novel genera comprising 12 species published to date. However, the ecological range and genomic diversity of the class are poorly understood. Taxonomic assignments within the class are unclear, limiting the ways in which data from 16S rRNA gene-based diversity studies in humans and rodent models are interpreted.

Whole-genome and 16S rRNA gene sequences of members of the class were analysed and assigned to the families , and . Inconsistencies between 16S rRNA gene sequence and whole genome sequence data deposited in public databases were identified. Newly annotated data searched against 85,000 16S rRNA gene sequence datasets included in the IMNGS (Integrated Microbial Next Generation Sequencing) database demonstrates humans and rodents harbour distinct populations. Members of the family predominate in the human gut, while are more representative of the rodent gut. Metabolic capabilities of the three families of vary greatly, with compared with and . Correct annotation of in 16S rRNA gene (and by extension shotgun metagenomic) datasets is required to determine the contributions of these increasingly important bacteria to different ecosystems.

  • This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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