Various health beneficial outcomes associated with red seaweeds, especially their polysaccharides, have been claimed, but the molecular pathway of how red seaweed polysaccharides are degraded and utilized by cooperative actions of human gut bacteria has not been elucidated. Here, we investigated the enzymatic and metabolic cooperation between two human gut symbionts, Bacteroides plebeius and Bifidobacterium longum ssp. infantis, with regard to the degradation of agarose, the main carbohydrate of red seaweed. More specifically, B. plebeius initially decomposed agarose into agarotriose by the actions of the enzymes belonging to glycoside hydrolase (GH) families 16 and 117 (i.e., BpGH16A and BpGH117) located in the polysaccharide utilization locus, a specific gene cluster for red seaweed carbohydrates. Then, B. infantis extracted energy from agarotriose by the actions of two agarolytic β-galactosidases (i.e., Bga42A and Bga2A) and produced neoagarobiose. B. plebeius ultimately acted on neoagarobiose by BpGH117, resulting in the production of 3,6-anhydro-l-galactose, a monomeric sugar possessing anti-inflammatory activity. Our discovery of the cooperative actions of the two human gut symbionts on agarose degradation and the identification of the related enzyme genes and metabolic intermediates generated during the metabolic processes provide a molecular basis for agarose degradation by gut bacteria.
Bibliographical noteFunding Information:
This work was supported by the Mid-career Researcher Program through the National Research Foundation of Korea (2020R1A2B5B02002631), by the Brain Pool Program through the Korean Federation of Science and Technology Societies funded by the Ministry of Science and ICT of Korea (2019H1D3A2A01100327), and by the Korea Institute of Planning and Evaluation for Technology in Food, Agriculture, Forestry, and Fisheries funded by the Ministry of Agriculture, Food, and Rural Affairs (321036051SB010). We also acknowledge the grant support by Korea University and the facility support by the Institute of Biomedical and Food Safety at CJ Food Safety Hall, Korea University.
© 2021, The Author(s).
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