Human gut Bacteroidetes can utilize yeast mannan through a selfish mechanism.

Cuskin, F., Lowe, E.C., Temple, M.J., Zhu, Y., Cameron, E.A., Pudlo, N.P., Abbott, D.W., and others (2015). "Human gut Bacteroidetes can utilize yeast mannan through a selfish mechanism.", Nature, 517(7533), pp. 165-169. doi : 10.1038/nature13995  Access to full text

Abstract

Yeasts, which have been a component of the human diet for at least 7,000 years, possess an elaborate cell wall α-mannan. The influence of yeast mannan on the ecology of the human microbiota is unknown. Here we show that yeast α-mannan is a viable food source for the Gram-negative bacterium Bacteroides thetaiotaomicron, a dominant member of the microbiota. Detailed biochemical analysis and targeted gene disruption studies support a model whereby limited cleavage of α-mannan on the surface generates large oligosaccharides that are subsequently depolymerized to mannose by the action of periplasmic enzymes. Co-culturing studies showed that metabolism of yeast mannan by Bacteroides thetaiotaomicron presents a ‘selfish’ model for the catabolism of this difficult to breakdown polysaccharide. Genomic comparison with Bacteroides thetaiotaomicron in conjunction with cell culture studies show that a cohort of highly successful members of the microbiota has evolved to consume sterically-restricted yeast glycans, an adaptation that may reflect the incorporation of eukaryotic microorganisms into the human diet.

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