Polymerization-dependent gut microbiome responses to curdlan β-1,3-glucan and its oligosaccharides.

β-1,3-Glucan is a dietary fiber with microbiome-modulating potential, yet the role of polymerization degree on microbial composition and metabolism remains unclear. Curdlan is an insoluble linear β-1,3-glucan widely used as a food hydrocolloid that provides a model to examine structure-dependent microbiome responses. We compared glucose, curdlan (CBG), and curdlan-derived β-1,3-glucan oligosaccharides (OBG) using anaerobic in vitro fermentation of pooled human feces. A multi-omics approach integrating 16S rRNA sequencing, shotgun metagenomics, short-chain fatty acid (SCFA) quantification, and untargeted metabolomics was applied to resolve taxonomic, functional, and metabolic shifts. Both CBG and OBG enriched Bacteroidota and enhanced carbohydrate metabolism relative to glucose, but through distinct pathways. CBG promoted polymer-associated carbohydrate processing, with enrichment of β-1,3-glucan-degrading enzymes such as GH16, Sus-like transport systems, and polysaccharide-specialized taxa (e.g., Prevotella and Bifidobacterium), and butyrate production. In contrast, OBG favored transporter-mediated substrate uptake, broader microbial participation (e.g. Parabacteroides and Enterobacteriaceae), and a metabolite profile enriched in amino acid-derived compounds and branched-chain SCFAs. These findings demonstrate that β-1,3-glucan polymerization degree governs microbiome functional routing and highlight polymerization degree as a tunable parameter for designing microbiome-directed carbohydrate ingredients with predictable metabolic outcomes.