Agaro-oligosaccharides (AOSs) are agar-derived oligosaccharides composed of D-galactose and 3,6-anhydro-L-galactose. This study investigated the effects of dietary AOS on colonic mucin-related markers and their relationships with the cecal microbiota and short-chain fatty acids (SCFAs) in normal mice. Female BALB/c mice received a control diet or a diet with 5% cellulose replaced by AOS for 28 days (six mice in two cages per group). Colonic mucin-related markers, cecal microbiota, and SCFAs were assessed alongside in vitro experiments using Akkermansia muciniphila and HT-29 cells. AOS increased colonic Alcian blue–periodic acid–Schiff-positive area, fecal mucin content, and colonic Muc2 and Spdef mRNA expression. 16S rRNA sequencing revealed higher Akkermansia abundance, while species-specific qPCR indicated a higher A. muciniphila-to-total bacterial 16S rRNA gene copy ratio. Cecal acetate, propionate, and butyrate concentrations decreased; estimated total amounts decreased for acetate and butyrate but not significantly for propionate. In vitro, AOS increased A. muciniphila culture OD₆₆₀ at 0.2–0.5% but decreased it at 1.0% and increased HT-29 MUC2 mRNA expression after 2 h. Despite limited cage-level replication and untested barrier function and microbial causality, these findings associate dietary AOS substitution with increased colonic mucin-related markers and a short-term MUC2 mRNA response in HT-29 cells.

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 .