-Glycoside-Metabolizing Human Gut Bacterium, sp. MRG-IFC3.

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 -glycoside-deglycosylating strain, sp. MRG-IFC3, was isolated from human fecal sample under anaerobic conditions. Though MRG-IFC3 biotransformed isoflavone -glycoside, it could not metabolize other -glycosides, such as vitexin, bergenin, and aloin. As evident from the production of the corresponding aglycons from various 7--glucosides, MRG-IFC3 strain also showed 7--glycoside cleavage activity; however, flavone 3--glucoside icariside II was not metabolized. In addition, for mechanism study, -glycosyl bond cleavage of puerarin by MRG-IFC3 strain was performed in DO GAM medium. The complete deuterium enrichment on C-8 position of daidzein was confirmed by H 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 -glycosidic bond cleavage at the molecular level.