Biochemical gut metabolism of dietary bioactive compounds is of great significance in elucidating health-related issues at the molecular level. In this study, a human gut bacterium cleaving C-C glycosidic bond was screened from puerarin conversion to daidzein, and a new, gram-positive C-glycoside-deglycosylating strain, Dorea sp. MRG-IFC3, was isolated from human fecal sample under anaerobic conditions. Though MRG-IFC3 biotransformed isoflavone C-glycoside, it could not metabolize other C-glycosides, such as vitexin, bergenin, and aloin. As evident from the production of the corresponding aglycons from various 7-O-glucosides, MRG-IFC3 strain also showed 7-O-glycoside cleavage activity; however, flavone 3-O-glucoside icariside II was not metabolized. In addition, for mechanism study, C-glycosyl bond cleavage of puerarin by MRG-IFC3 strain was performed in D2O GAM medium. The complete deuterium enrichment on C-8 position of daidzein was confirmed by 1H NMR spectroscopy, and the result clearly proved for the first time that daidzein is produced from puerarin. Two possible reaction intermediates, the quinoids and 8-dehydrodaidzein anion, were proposed for the production of daidzein-8d. These results will provide the basis for the mechanism study of stable C-glycosidic bond cleavage at the molecular level.
Keywords: C-C bond cleavage; C-glycoside; Dorea sp. MRG-IFC3; gut metabolism; puerarin.