RESUMO
The metabolism of carbohydrate polymers drives microbial diversity in the human gut microbiota. It is unclear, however, whether bacterial consortia or single organisms are required to depolymerize highly complex glycans. Here we show that the gut bacterium Bacteroides thetaiotaomicron uses the most structurally complex glycan known: the plant pectic polysaccharide rhamnogalacturonan-II, cleaving all but 1 of its 21 distinct glycosidic linkages. The deconstruction of rhamnogalacturonan-II side chains and backbone are coordinated to overcome steric constraints, and the degradation involves previously undiscovered enzyme families and catalytic activities. The degradation system informs revision of the current structural model of rhamnogalacturonan-II and highlights how individual gut bacteria orchestrate manifold enzymes to metabolize the most challenging glycan in the human diet.
Assuntos
Bacteroides thetaiotaomicron/enzimologia , Bacteroides thetaiotaomicron/metabolismo , Biocatálise , Trato Gastrointestinal/microbiologia , Glicosídeo Hidrolases/metabolismo , Pectinas/química , Pectinas/metabolismo , Bacteroides thetaiotaomicron/crescimento & desenvolvimento , Boratos/química , Boratos/metabolismo , Domínio Catalítico , Microbioma Gastrointestinal , Glicosídeo Hidrolases/química , Glicosídeo Hidrolases/classificação , Humanos , Modelos Moleculares , Especificidade por SubstratoRESUMO
An enzymatic method for specific determination of stevioside content was established. Recombinant ß-glucosidase BT_3567 (rBT_3567) from Bacteroides thetaiotaomicron HB-13 exhibited selective hydrolysis of stevioside at ß-1,2-glycosidic bond to yield rubusoside and glucose. Coupling of this enzyme with glucose oxidase and peroxidase allowed for quantitation of stevioside content in Stevia samples by using a colorimetric-based approach. The series of reactions for stevioside determination can be completed within 1 h at 37 °C. Stevioside determination using the enzymatic assay strongly correlated with results obtained from HPLC quantitation (r2 = 0.9629, n = 16). The percentages of coefficient variation (CV) of within day (n = 12) and between days (n = 12) assays were lower than 5%, and accuracy ranges were 95-105%. This analysis demonstrates that the enzymatic method developed in this study is specific, easy to perform, accurate, and yields reproducible results.