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

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 04mmoll(-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 14mmoll(-1). Our results demonstrated that E.coli whole-cell is an efficient biocatalyst for biosynthesis of isoflavone metabolites under aerobic conditions.