Heterologous expression of equol biosynthesis genes from Adlercreutzia equolifaciens

Equol is the isoflavone-derived metabolite with the greatest estrogenic and antioxidant activity. It is produced from daidzein by fastidious and oxygen-susceptible intestinal bacteria, which hinders their use at an industrial scale. Therefore, expressing the equol production machinery into easily-cultivable hosts would expedite the heterologous production of this compound. In this work, four genes (racemase, tdr, ddr and dzr) coding for key enzymes involved in equol production in Adlercreutzia equolifaciens DSM19450T were synthesized and cloned in a pUC-derived vector (pUC57-equol) that was introduced in Escherichia coli. Recombinant clones of E. coli produced equol in cultures supplemented with daidzein (equol precursor) and dihydrodaidzein (intermediate compound). To check whether equol genes were expressed in Gram-positive bacteria, the pUC57-equol construct was cloned into the low-copy-number vector pIL252, and the new construct (pIL252-pUC57-equol) introduced into model strains of Lacticaseibacillus casei and Lactococcus lactis. L. casei clones carrying pIL252-pUC57-equol produced a small amount of equol from dihydrodaidzein but not from daidzein, while L. lactis recombinant clones produced no equol from either of the substrates. This is the first time that A. equolifaciens equol genes have been cloned and expressed in heterologous hosts. E. coli clones harboring pUC57-equol could be used for biotechnological production of equol.