Anaerostipes stercorihominis sp. nov., isolated from human faeces

The genus Anaerostipes is one of the major butyrate-producing genera in the gut microbiota of healthy human adults. During a culturomics study of the human gut, strain 17EGHSPOS18-1^T was isolated from the faeces of a healthy adult. Here, we conducted a taxonomic study of the strain. Phylogenetic analysis based on 16S rRNA gene sequences placed strain 17EGHSPOS18-1ᵀ in the Anaerostipes cluster. This placement was supported by a core gene-based phylogenetic analysis. Strain 17EGHSPOS18-1^T shared average nucleotide identity (ANI) values of <80% and digital DNA-DNA hybridization (dDDH) values of <30% with known Anaerostipes spp., indicating that it does not belong to any known species of the genus Anaerostipes. Physiological and chemotaxonomic characteristics, including carbohydrate utilization patterns, enzyme activities, major cellular fatty acid profiles and major fermentation end-product profiles, further distinguished the strain from the known Anaerostipes spp. The novel strain was able to metabolize only a limited number of carbohydrates, consistent with its restricted repertoire of glycoside hydrolase family proteins. These findings indicate that 17EGHSPOS18-1^T represents a novel species, for which the name Anaerostipes stercorihominis sp. nov. is proposed. The type strain is 17EGHSPOS18-1^T (= JCM 38261^T = DSM 121506^T). Furthermore, during this taxonomic study, we found that Anaerostipes hominis and Anaerostipes faecis share ANI and dDDH values above the species discrimination thresholds, indicating that they should be assigned to the same taxon. Based on the data, we propose A. faecis as a later heterotypic synonym of A. hominis.