Generation of novel prebiotic oligosaccharide pools from fiber drives biological insight in bacterial glycan metabolism.

Prebiotic oligosaccharides are dietary supplements that modulate the intestinal gut microbiome by selectively nourishing subsets of the microbial community with a goal to enhance host health. To date, the diversity of polysaccharide compositions in the fiber consumed by humans is not well represented by the limited scope of oligosaccharide compositions present in current commercial prebiotics. Recently, our UC Davis group developed a novel method to generate oligosaccharides from any polysaccharide fiber, termed Fenton's Initiation Toward Defined Oligosaccharide Groups (FITDOG). Using this method, sugar beet pulp (SBP) was transformed into sugar beet oligosaccharides (SBOs) composed of arabinose- and galactose-containing oligosaccharides. Fecal fermentations of SBO and SBP produced similar shifts in donor-specific bacterial communities and acid metabolite profiles with a general enrichment of Bacteroides and Bifidobacterium. However, in vitro tests revealed more Bifidobacterium strains could consume SBO than sugar beet arabinan, and specific strains showed differential consumption of arabinofuranooligosaccharides or galactooligosaccharide (GOS) portions of the SBO pool. Genomic and glycomic comparisons suggest that previously characterized, arabinan-specific, extracellular arabinofuranosidases from Bifidobacterium are not necessary to metabolize the arabino-oligosaccharides within SBO. Synbiotic application of SBO with an SBO-consuming strain Bifidobacterium longum subsp. longum SC596 in serial fecal enrichments resulted in enhanced persistence among 9 of 10 donor feces. This work demonstrates a novel workflow whereby FITDOG creates novel oligosaccharide pools that can provide insight into how compositional differences in fiber drive differential gut fermentation behaviors as well as their downstream health impacts. Moreover, these oligosaccharides may be useful in new prebiotic and synbiotic applications.IMPORTANCEPrebiotics seek to selectively alter the host microbiome composition or function, resulting in a concurrent health benefit to the host. However, commercial prebiotics represent a small fraction of the diversity of food polysaccharide compositions. In this work a novel method, Fenton's Initiation Toward Defined Oligosaccharide Groups (FITDOG) was used to generate an oligosaccharide pool from sugar beet pulp (SBP). Sugar beet oligosaccharides (SBOs) resulted in similar changes to SBP in fecal enrichments; however, SBO could be consumed by more beneficial bifidobacterial strains than the cognate polysaccharide. These results demonstrate how the details of glycan structure have a profound influence on how gut bacteria metabolize food carbohydrates. The implications of this work are relevant to understanding how different dietary sources influence the human microbiome and extend to developing novel oligosaccharide pools for prebiotic applications.