Mucin Glycoprotein Degradation by Mucin Oligosaccharide-degrading Strains of Human Faecal Bacteria. Characterisation of Saccharide Cleavage Products and their Potential Role in Nutritional Support of Larger Faecal Bacterial Populations

Abstract

A subset of normal human faecal bacteria composed of mucin oligosaccharide-degrading (MOD) strains appears to be the principal source of intraluminal, extracellular glycosidases degrading the oligosaccharides of gut mucin glycoproteins and epithelial membrane glycoconjugates. Here we report studies characterising the saccharides released from hog gastric mucin during incubation with the extracellular enzymes in their cell-free culture supernates. We have also tested the ability of the saccharide products to support growth of larger populations of faecal bacteria.Gel exclusion chromatography of the residual mucin following bacterial growth in mucin-containing medium confirmed that MOD strains extensively degraded the carbohydrate moieties (60–96 per cent) whereas strains of bacteroides and bifidobacteria of larger faecal populations degraded the carbohydrate moieties less extensively (median loss, 29 per cent; range 8–42 per cent). Saccharides released from hog gastric mucin by MOD strain enzymes were identified by biochemical and NMR spectroscopic methods as galactose, fucose. N-acetylglucosaminc, N-acetylgalactosamme and the disaccharides Galβ3GalNAc and Galβ3GlcNAc. Larger oligosaccharides were not recovered. Carbon-13 NMR spectra of the residual mucin were consistent with complete removal of some but not all oligosaccharide chains. The monosaccharides but not the disaccharides were also recovered following incubation of mucin with the sterile cell-free supernate of a heavily inoculated faecal culture. Saccharides released from hog gastric mucin by partially purified culture supernate enzymes from Ruminococcus torques strain IX-70 were 70–98 per cent utilised by larger populations of faecal bacteria during growth in culture. Bacteria growing from 1 × 10−10 g faecal inocula from five subjects showed minimal growth in media containing intact hog gastric mucin but grew well if the mucin-containing medium was preincubated with a sterile enzyme preparation from R. torques IX-70. We conclude that glycosidases produced by MOD strains can serve a nutritionally supportive role for larger populations of enteric bacteria, especially during fasting.