Cross-feeding interactions of gut microbes mediated by O-linked glycans from casein glycomacropeptide

The human gut microbiota plays an essential role in metabolizing complex compounds that host enzymes cannot degrade in the diet. In turn, the gut microbiota has the ability to interact with the host through mucus that protects epithelium cells. O-glycans have been proposed as emerging prebiotics due to their similarity to hostassociated glycans instead of plant-derived prebiotics. Some gut microbes have been described to utilize the O-glycans as carbon sources for colonization. Changes in the protective barrier of host cells are linked to intestinal diseases. For this reason, trophic networks of microbial interactions play an important role in establishing a microbiome beneficial to the host's health. Glycromacropeptide (GMP) is an O-glycopeptide obtained from whey during cheese manufacture. GMP could be considered as a simple model of O-glycans to analyze the molecular mechanisms involved in metabolic interactions between gut microbes. This work aimed to determine the molecular strategies and microbial interactions while utilizing glycomacropeptide as a carbon source. Individual cultures of representative bacteria allowed the identification of the major GMP-degraders. Unidirectional assays identified galacto-N-biose, galactose, N-Acetylgalactosamine, and sialic acid as by-products, providing a perspective on microbial interactions during GMP fermentation. Bidirectional assays demonstrated cross-feeding activity and competition between gut microbes, in addition to the promotion of butyrate from the fatty acids derived from the use of GMP. O-glycan-specific enzyme expression was identified for B. infantis ATCC 15697 and B. bifidum JCM 1254 during GMP cross-feeding consumption. This study highlights strategies for utilizing O-glycans in GMP consumption among gut microbes.