Dynamics of tryptophan metabolites and microbial adaptations during corn by-product fermentation in the pig gut microbiome

BACKGROUND: Food by-products, such as corn germ meal from starch processing, are increasingly used as sustainable feed supplements, reducing competition between food and feed and supporting the valorisation of food waste. However, their effects on gut microbial metabolism and host health remain unclear. This study aimed to determine how corn germ meal fermentation influences microbial community structure and metabolite production using an ex vivo pig faecal culture system. RESULTS: Corn germ meal supplementation significantly altered the microbial composition, increasing diversity and enriching fibre-degrading Prevotellaceae, a key bacterial family involved in complex carbohydrate metabolism. Metabolomic analysis revealed marked increases in tryptophan-derived metabolites, including indoleacrylic acid, indolepropionic acid, and indolelactic acid, which act as ligands for the aryl hydrocarbon receptor and have anti-inflammatory properties. Prevotella-mediated catabolite repression reduced Escherichia coli-derived indole formation, redirecting microbial tryptophan metabolism toward the production of these bioactive compounds. Microbial and metabolic responses differed among farms, reflecting farm-specific microbiome structures. CONCLUSIONS: Corn germ meal supplementation reshapes gut microbial communities, enhances metabolic activity, and promotes the generation of bioactive tryptophan metabolites with potential immunomodulatory effects. These findings highlight the value of corn by-products as dietary fibres that can drive beneficial microbial cross-feeding and influence host intestinal homeostasis. Although demonstrated in an ex vivo setting, this study provides a mechanistic basis and preclinical evidence for future in vivo studies, supporting the sustainable utilisation of food industry by-products to improve gut health and resource efficiency in livestock production.