Isolation and identification of a human intestinal bacterium capable of daidzein conversion

Equol, which produced from daidzein (one of the principal isoflavones), is recognized to be the most resultful in stimulating an estrogenic and antioxidant response. The daidzein transformation was studied during fermentation of five growth media inoculated with feces from a healthy human, and a daidzein conversion strain was isolated. To enrich the bacterial population involved in daidzein metabolism in a complex mixture, fecal samples were treated with antibiotics. The improved propidium monoazide combined with the quantitative polymerase chain reaction (PMAxx-qPCR) assay showed that the ampicillin treatment of samples did result in a reduction of the total visible bacteria counts by 52.2% compared to the treatment without antibiotics. On this basis, the newly isolated rod-shaped, Gram-positive anaerobic bacterium, named strain Y11 (MN560033), was able to metabolize daidzein to equol under anaerobic conditions, with a conversion ratio (equol ratio: the amount of equol produced/amount of supplemented daizein) of 0.56 over 120 h. The 16S rRNA partial sequence of the strain Y11 exhibited 99.8% identity to that of Slackia equolifaciens strain DZE (NR116295). This study will provide new insights into the biotransformation of equol from daidzein by intestinal microbiota from the strain-level and explore the possibility of probiotic interventions.