Syntrophic interactions in the digestion of fungal β-glucan by the gut microbiota

Fernández Juliá, Pedro Jesús (2023) Syntrophic interactions in the digestion of fungal β-glucan by the gut microbiota. Doctoral thesis, Northumbria University.

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Abstract

The human gut microbiota (HGM) contributes to the physiology and health of the host. The health benefits provided by dietary manipulation of the HGM require knowledge of how glycans are metabolized. β-glucans are polysaccharides that can be obtained from different sources, and which have been described as potential prebiotics since they support the growth of gut-associated bacteria, including members of the genera Bacteroides, Bifidobacterium and Lactobacillus. Nevertheless, the mechanism of action underpinning these health effects has been subject to debate and revision. By using alkaline extraction, β-glucan was purified from the fungi Fusarium venenatum, and it was consumed by certain members of the genus Bacteroides as primary degraders, although the ability to degrade the intact polysaccharide was also tested in some members of the genera Roseburia, Akkermansia and Victivallis. It was shown that Bacteroides cellulosyliticus WH2, Bacteroides thetaiotaomicron VPI 5482 and Bacteroides vulgatus ATCC 8482 express specific enzymes to degrade Fusarium β- glucan, thereby releasing short-chain fatty acids and oligosaccharides into the growth medium. Using a cross-feeding approach, those oligosaccharides were purified and then utilized as carbon source for members of the genera Bifidobacterium and Lactiplantibacillus, which acted as secondary degraders. Finally, they were grown in cocultures with Bacteroides species. Using colony counting and qPCR, it was shown that both primary and secondary degraders grew in the coculture by establishing syntrophic interactions when Fusarium β-glucan acted as carbon source. The data obtained points out the potential prebiotic effect that Fusarium β-glucan may have as a polysaccharide substrate for different members of the Human Gut Microbiota.

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