Gut bacteria play a key role in the metabolism of dietary isoflavones, thereby influencing the availability and bioactivation of these polyphenols in the intestine. The human intestinal bacterium Slackia isoflavoniconvertens converts the main soybean isoflavones daidzein and genistein to equol and 5-hydroxy-equol, respectively. Cell extracts of S. isoflavoniconvertens catalyzed the conversion of daidzein via dihydrodaidzein to equol and that of genistein to dihydrogenistein. Growth of S. isoflavoniconvertens in the presence of daidzein led to the induction of several proteins as observed by two-dimensional difference gel electrophoresis. Based on determined peptide sequences, we identified a cluster of eight genes encoding the daidzein-induced proteins. Heterologous expression of three of these genes in Escherichia coli and enzyme activity tests with the resulting cell extracts identified the corresponding gene products as a daidzein reductase (DZNR), a dihydrodaidzein reductase (DHDR), and a tetrahydrodaidzein reductase (THDR). The recombinant DZNR also converted genistein to dihydrogenistein at higher rates than were observed for the conversion of daidzein to dihydrodaidzein. Higher rates were also observed with cell extracts of S. isoflavoniconvertens. The recombinant DHDR and THDR catalyzed the reduction of dihydrodaidzein to equol, while the corresponding conversion of dihydrogenistein to 5-hydroxy-equol was not observed. The DZNR, DHDR, and THDR were expressed as Strep-tag fusion proteins and subsequently purified by affinity chromatography. The purified enzymes were further characterized with regard to their activity, stereochemistry, quaternary structure, and content of flavin cofactors.
A rod-shaped gram-positive anaerobic bacterium, strain HE8, was isolated from human feces. The isolate was able to convert the isoflavones daidzein and genistein to equol and 5-hydroxy-equol, respectively. Based on phenotypic and phylogenetic analyses, strain HE8 is described as a new species, Slackia isoflavoniconvertens.
HighlightsGenetically modified Bacillus subtilis identified in a vitamin B2 product.Whole genome sequencing runs are performed for characterization of the isolated strain.Complex modifications of the genome are identified.Four putative recombinant plasmids are characterized.Real-time PCR methods are developed and available for testing vitamin B2 products.
Intestinal conversion of the isoflavone daidzein to the bioactive equol is exclusively catalyzed by gut bacteria, but a direct role in equol formation under in vivo conditions has not yet been demonstrated. Slackia isoflavoniconvertens is one of the few equol-forming gut bacteria isolated from humans and, moreover, it also converts genistein to 5-hydroxy-equol. To demonstrate the isoflavone-converting ability of S. isoflavoniconvertens in vivo, the metabolization of dietary daidzein and genistein was investigated in male and female rats harboring a simplified human microbiota without (control) or with S. isoflavoniconvertens (SIA). Feces, urine, intestinal contents, and plasma of the rats were analyzed for daidzein, genistein, and their metabolites. Equol and 5-hydroxy-equol were found in intestinal contents, feces, and urine of SIA rats but not in the corresponding samples of the control rats. 5-Hydroxy-equol was present at much lower concentrations than equol and the main metabolite produced from genistein was the intermediate dihydrogenistein. The plasma of SIA rats contained equol but no 5-hydroxy-equol. Equol formation had no effect on plasma concentrations of the insulin-like growth factor I. The concentrations of daidzein and genistein were considerably lower in all samples of the SIA rats than in those of the control rats. Male SIA rats had higher intestinal and fecal concentrations of the isoflavones and their metabolites than female SIA rats. The observed activity in the rat model indicates that S. isoflavoniconvertens is capable of contributing in vivo to the bioactivation of daidzein and genistein by formation of equol and 5-hydroxy-equol.
The metabolism of isoflavones by gut bacteria plays a key role in the availability and bioactivation of these compounds in the intestine. Daidzein and genistein are the most common dietary soy isoflavones. While daidzein conversion yielding equol has been known for some time, the corresponding formation of 5-hydroxyequol from genistein has not been reported previously. We isolated a strictly anaerobic bacterium (Mt1B8) from the mouse intestine which converted daidzein via dihydrodaidzein to equol as well as genistein via dihydrogenistein to 5-hydroxy-equol. Strain Mt1B8 was a gram-positive, rod-shaped bacterium identified as a member of the Coriobacteriaceae. Strain Mt1B8 also transformed dihydrodaidzein and dihydrogenistein to equol and 5-hydroxy-equol, respectively. The conversion of daidzein, genistein, dihydrodaidzein, and dihydrogenistein in the stationary growth phase depended on preincubation with the corresponding isoflavonoid, indicating enzyme induction. Moreover, dihydrogenistein was transformed even more rapidly in the stationary phase when strain Mt1B8 was grown on either genistein or daidzein. Growing the cells on daidzein also enabled conversion of genistein. This suggests that the same enzymes are involved in the conversion of the two isoflavones.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.