Bacteria of the human intestinal microbiota produce glycosidases specific for lacto-series glycosphingolipids.

Five strains of human fecal bacteria, of the Ruminococcus and Bifidobacterium genera, produce extracellular alpha- and beta-glycosidases that degrade intestinal mucin oligosaccharides and glycosphingolipids of the lacto-series type 1 chain. We have tested the activities and substrate specificities of these enzymes using para-nitrophenyl glycosides and glycosphingolipids of different core chains (lacto, neolacto, globo, isoglobo, galabio, and ganglio), carrying different blood group determinants (A, H, X, Y, Forssman, and para-Forssman), and with different degrees of sialylation (mono- to tetra-sialo). Lactotetraosylceramide and neolactotetraosylceramide were the only core glycosphingolipids degraded by enzymes from these strains, resulting in lactosylceramide and glucosylceramide as the major end products. R. gnavus strain VI-268 did not degrade lactotetraosylceramide but only neolactotetraosylceramide yielding lactotriaosylceramide and lactosylceramide as the major end products. All strains but R. gnavus VI-268 also produced lactosylceramide from a bi-antennary 10-sugar glycosphingolipid with two blood group H determinants based on a lactotetraosylceramide core. Apart from strain specific blood group A-degrading (R. torques strain VIII-239 and IX-70, R. gnavus strain VI-268 and B. infantis VIII-240) and Forssman-degrading (R. torques VIII-239 and IX-70) activities, all strains also degraded the H-5, X-5, and Y-6 glycosphingolipids. All strains released N-acetylneuraminic acid from the gangliosides sialosyl-neolactotetraosylceramide, GD3, GD1a, GD1b, GT1b, and GQ1b corresponding to 2,3-alpha- and 2,8-alpha-N-acetylneuraminidase activities. The R. torques strains VIII-239 and IX-70 also partially desialylated GM1 to lactotetraosylceramide. The para-nitrophenyl glycoside degradations were often incompatible with the data from the glycosphingolipids degradations.(ABSTRACT TRUNCATED AT 250 WORDS)