Alginate oligosaccharide assimilation by gut microorganisms and the potential role in gut inflammation alleviation.

Dietary fiber metabolism by gut microorganisms plays important roles in host physiology and health. Alginate, the major dietary fiber of daily diet seaweeds, is drawing more attention because of multiple biological activities. To advance the understanding of alginate assimilation mechanism in the gut, we show the presence of unsaturated alginate oligosaccharides (uAOS)-specific alginate utilization loci (AUL) in human gut microbiome. As a representative example, a working model of the AUL from the gut microorganism Bacteroides clarus was reconstructed from biochemistry and transcriptome data. The fermentation of resulting monosaccharides through Entner-Doudoroff pathway tunes the metabolism of short-chain fatty acids and amino acids. Furthermore, we show that uAOS feeding protects the mice against dextran sulfate sodium-induced acute colitis probably by remodeling gut microbiota and metabolome.

Importance: Alginate has been included in traditional Chinese medicine and daily diet for centuries. Recently discovered biological activities suggested that alginate-derived alginate oligosaccharides (AOS) might be an active ingredient in traditional Chinese medicine, but how these AOS are metabolized in the gut and how it affects health need more information. The study on the working mechanism of alginate utilization loci (AUL) by the gut microorganism uncovers the role of unsaturated alginate oligosaccharides (uAOS) assimilation in tuning short-chain fatty acids and amino acids metabolism and demonstrates that uAOS metabolism by gut microorganisms results in a variation of cell metabolites, which potentially contributes to the physiology and health of gut.