Reduction of soy isoflavones by use of Escherichia coli whole-cell biocatalyst expressing isoflavone reductase under aerobic conditions.

UNLABELLED: Soy isoflavone metabolites are currently receiving much attention due to the stronger and wider bioactivities than that of isoflavones. Therefore, biosynthesis of isoflavone metabolites by isolated isoflavone biotransforming bacteria is important. However, the biosynthesis process must be under obligate anaerobic conditions due to the reduction reactions catalysed by isoflavone biotransforming bacteria. In this study, we cloned the daidzein and genistein reductase gene (dgr) from Slackia sp. AUH-JLC159. The recombinant Escherichia coli (E. coli) whole-cell was used for the first time as the biocatalyst for aerobic biosynthesis of dihydrodaidzein (DHD) and dihydrogenistein (DHG) from soy isoflavones daidzein and genistein. Our results indicated that the recombinant E. coli whole-cell was able to reduce daidzein and genistein to DHD and DHG under aerobic conditions, while the maximal concentration of the substrate daidzein or genistein that the E. coli whole-cell was able to convert efficiently was only 0·4 mmol l(-1) . Under the optimized conditions, the maximal concentration of daidzein or genistein that the E. coli whole-cell was able to convert efficiently was increased to 1·4 mmol l(-1) . Our results demonstrated that E. coli whole-cell is an efficient biocatalyst for biosynthesis of isoflavone metabolites under aerobic conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: Soy isoflavone metabolites, which are more biologically active than their precursor isoflavones, are currently receiving much more attention. However, the non-natural isoflavone metabolites are synthesized or biosynthesized under obligate anaerobic conditions. Here, we describe a new approach to the reduction of soy isoflavones daidzein and genistein under aerobic conditions by use of the recombinant Escherichia coli whole-cell expressing isoflavone reductase. Our study provides the first evidence that isoflavone metabolites, such as dihydrodaidzein and dihydrogenistein, are able to be produced efficiently under aerobic conditions.