Abstract
The structure of the human gut microbiota is controlled primarily through the degradation of complex dietary carbohydrates, but the extent to which carbohydrate breakdown products are shared between members of the microbiota is unclear. We show here, using xylan as a model, that sharing the breakdown products of complex carbohydrates by key members of the microbiota, such as Bacteroides ovatus, is dependent on the complexity of the target glycan. Characterization of the extensive xylan degrading apparatus expressed by B. ovatus reveals that the breakdown of the polysaccharide by the human gut microbiota is significantly more complex than previous models suggested, which were based on the deconstruction of xylans containing limited monosaccharide side chains. Our report presents a highly complex and dynamic xylan degrading apparatus that is fine-tuned to recognize the different forms of the polysaccharide presented to the human gut microbiota.
Highlights
The structure of the human gut microbiota is controlled primarily through the degradation of complex dietary carbohydrates, but the extent to which carbohydrate breakdown products are shared between members of the microbiota is unclear
Genomic and metagenomic data show that the catabolism of complex dietary carbohydrates (CDCs), known as dietary fibre, play a central role in defining the structure of the human gut microbiota (HGM)[1,2]
Our data show that B. ovatus has evolved a highly dynamic xylan degrading system that can respond to the different forms of the xylose polymer
Summary
The structure of the human gut microbiota is controlled primarily through the degradation of complex dietary carbohydrates, but the extent to which carbohydrate breakdown products are shared between members of the microbiota is unclear. We show here, using xylan as a model, that sharing the breakdown products of complex carbohydrates by key members of the microbiota, such as Bacteroides ovatus, is dependent on the complexity of the target glycan. Characterization of the extensive xylan degrading apparatus expressed by B. ovatus reveals that the breakdown of the polysaccharide by the human gut microbiota is significantly more complex than previous models suggested, which were based on the deconstruction of xylans containing limited monosaccharide side chains. Current strategies deployed to manipulate the composition of the HGM to maximize human health are centred on the use of complex carbohydrates (prebiotics)[7] to encourage the expansion of beneficial (probiotic) microorganisms[8] The effects of these strategies are dependent on the glycan food web in the HGM9,10. Polysaccharide breakdown products (PBPs) are released during degradation of both simple and complex xylans by B. ovatus, the ability of other members of the HGM to use these PBPs is dictated by the complexity of the target xylan
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