Abstract
The intake of isoflavones is presumed to be associated with health benefits in humans, but also potential adverse effects of isoflavones are controversially discussed. Isoflavones can be metabolized by gut bacteria leading to modulation of the bioactivity, such as estrogenic effects. Especially bacterial strains of the Eggerthellaceae, a well-known bacterial family of the human gut microbiota, are able to convert the isoflavone daidzein into equol. In addition, metabolization of genistein is also described for strains of the Eggerthellaceae. The aim of this study was to identify and investigate gut bacterial strains of the family Eggerthellaceae as well as the narrowly related family Coriobacteriaceae which are able to metabolize daidzein and genistein. This study provides a comprehensive, polyphasic approach comprising in silico analysis of the equol gene cluster, detection of genes associated with the daidzein, and genistein metabolism via PCR and fermentation of these isoflavones. The in silico search for protein sequences that are associated with daidzein metabolism identified sequences with high similarity values in already well-known equol-producing strains. Furthermore, protein sequences that are presumed to be associated with daidzein and genistein metabolism were detected in the two type strains ‘Hugonella massiliensis’ and Senegalimassilia faecalis which were not yet described to metabolize these isoflavones. An alignment of these protein sequences showed that the equol gene cluster is highly conserved. In addition, PCR amplification supported the presence of genes associated with daidzein and genistein metabolism. Furthermore, the metabolism of daidzein and genistein was investigated in fermentations of pure bacterial cultures under strictly anaerobic conditions and proofed the metabolism of daidzein and genistein by the strains ‘Hugonella massiliensis’ DSM 101782T and Senegalimassilia faecalis KGMB04484T.
Highlights
IntroductionTwo isoflavones with a very similar molecular structure, are well-known to be present in soy and soy-based food [1]
Daidzein and genistein, two isoflavones with a very similar molecular structure, are well-known to be present in soy and soy-based food [1]
Showed an identity of 100% of the nucleotide sequences. The aim of this in silico study was to identify strains of the Eggerthellaceae and Coriobacteriaceae which harbor genes involved in daidzein and genistein metabolism
Summary
Two isoflavones with a very similar molecular structure, are well-known to be present in soy and soy-based food [1]. Daidzein and genistein belong to the phytoestrogens as they are “biologically active phenolic compounds derived from plants” with “structures similar to the principal mammalian estrogen” [2]. Potential adverse effects of isoflavone intake are controversially discussed [4]. These effects are often associated with their estrogenic activity. For isoflavones the endogenous transformation in humans is well known and they can be metabolized by endogenous phase I and phase II enzymes [4]
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