Structural characterization of a galactan from Dioscorea opposita Thunb. and its bioactivity on selected Bacteroides strains from human gut microbiota.

Dioscorea opposita Thunb. is widely used as functional foods and traditional Chinese medicine in China for its activity of regulating function of spleen and stomach. Polysaccharides may contribute to the function of regulation. To investigate structure features and bioactivities of polysaccharides from D. opposita, the rhizome of D. opposita was extracted with boiling water, yielding crude polysaccharides DOP. A novel polysaccharide named DOP0.1-S-1 was isolated from DOP by further purification. The average molecular weight of DOP0.1-S-1 was 10,000 Da and the range was around 12,000 -1,200 Da. The carbohydrate content of DOP0.1-S-1 was 100% and no protein was detected. The monosaccharide analysis showed that DOP0.1-S-1 was mostly composed of galactose. Methylation and NMR spectra analysis indicated that DOP0.1-S-1 was a 1,4-ß-galactan. Bioactivity test showed that DOP0.1-S-1 could promote the growth of B. thetaiotaomicron and B. ovatus and produce the short-chain fatty acids during the utilization of the polysaccharide.

Nonmicrobicidal Small Molecule Inhibition of Polysaccharide Metabolism in Human Gut Microbes: A Potential Therapeutic Avenue.

A new approach for the nonmicrobicidal phenotypic manipulation of prominent gastrointestinal microbes is presented. Low micromolar concentrations of a chemical probe, acarbose, can selectively inhibit the Starch Utilization System and ablate the ability of Bacteroides thetaiotaomicron and B. fragilis strains to metabolize potato starch and pullulan. This strategy has potential therapeutic relevance for the selective modulation of the GI microbiota in a nonmicrobicidal manner.

Prebiotic galactooligosaccharides activate mucin and pectic galactan utilization pathways in the human gut symbiont Bacteroides thetaiotaomicron.

Galactooligosaccharides (GOS) are prebiotic carbohydrates that impart changes in the gut bacterial composition of formula-fed infants to more closely resemble that of breast-fed infants. Consuming human milk oligosaccharides (HMOs) provides specific bacterial strains with an advantage for colonizing the infant intestine. These same effects are seen in infants after GOS consumption, however GOS are very complex mixtures and the underlying molecular mechanisms of how GOS mimic HMOs are relatively unknown. Here we studied the effects of GOS utilization on a prominent gut symbiont, Bacteroides thetaiotaomicron, which has been previously shown to consume HMOs via mucin O-glycan degradation pathways. We show that several pathways for targeting O-mucin glycans are activated in B. thetaiotaomicron by GOS, as well as the galactan utilization sytem. Characterization of the endo-galactanase from this system identified activity on various longer GOS substrates while a subset of GOS compounds were identified as potential activators of mucin glycan metabolism in B. thetaiotaomicron. Our results show that GOS functions as an inducer of mucin-glycan pathways while providing a nutrient source in the form of ß-(1 → 4)-galactan. These metabolic features of GOS mixtures may serve to explain the beneficial effects that are seen for GOS supplemented infant formula.