The importance of the dihydrodaidzein racemase and dihydrodaidzein reductase activities and the host microorganism to achieve an efficient equol production by engineered lactic acid bacteria

Abstract

Abstract Equol is an isoflavone produced from daidzein by the microbial metabolism and it is of great interest for human health. Since equol production was described in bacteria that are difficult to grow and considered unsafe, the heterologous expression of genes involved in equol production in Generally Recognized As Safe (GRAS) and easily culturable bacteria is of great interest for the production of equol in large quantities. The heterologous expression of daidzein reductase (dzr), dihydrodaidzein reductase (ddr), tetrahydrodaidzein reductase (tdr) and dihydrodaidzein racemase (ifcA) from Slakia isoflavoniconvertens DSM 22006 in GRAS bacteria demonstrated that these bacteria were capable of producing equol from dihydrodaidzein (DHD), but only a few strains could produce equol from daidzein, always in low concentrations, with the exception of Limisolactobacillus fermentum INIA 584L and Limosilactobacillus fermentum INIA 832L. This study demonstrated that lactic acid bacteria can be engineered to produce bioactive compounds such as equol with high efficiency and the much higher production of equol by these strains was due to the greater activities of dihydrodaidzein racemase (DDRC), which acts in conjunction with daidzein reductase to produce DHD (S), and dihydrodaidzein reductase (DHDR), which may be related with the reducing power. In addition, the heterologous expression of ddr in GRAS bacteria produced equol and dehydroequol from DHD in addition to tetrahydrodaidzein.