High Titer of (S)-Equol Synthesis from Daidzein in Escherichia coli

Exploring functional genes' correlation with (S)-equol concentration and new daidzein racemase identification

With its estrogenic activity, (S)-equol plays an important role in maintaining host health and preventing estrogen-related diseases. Exclusive production occurs through the transformation of soy isoflavones by intestinal bacteria, but the reasons for variations in (S)-equol production among different individuals and species remain unclear. Here, fecal samples from humans, pigs, chickens, mice, and rats were used as research objects. The concentrations of (S)-equol, along with the genetic homology and evolutionary relationships of (S)-equol production-related genes [daidzein reductase (DZNR), daidzein racemase (DDRC), dihydrodaidzein reductase (DHDR), tetrahydrodaidzein reductase (THDR)], were analyzed. Additionally, in vitro functional verification of the newly identified DDRC gene was conducted. It was found that approximately 40% of human samples contained (S)-equol, whereas 100% of samples from other species contained (S)-equol. However, there were significant variations in (S)-equol content among the different species: rats > pigs > chickens > mice > humans. The distributions of the four genes displayed species-specific patterns. High detection rates across various species were exhibited by DHDR, THDR, and DDRC. In contrast, substantial variations in detection rates among different species and individuals were observed with respect to DZNR. It appears that various types of DZNR may be associated with different concentrations of (S)-equol, which potentially correspond to the regulatory role during (S)-equol synthesis. This enhances our understanding of individual variations in (S)-equol production and their connection with functional genes in vitro. Moreover, the newly identified DDRC exhibits higher potential for (S)-equol synthesis compared to the known DDRC, providing valuable resources for advancing in vitro (S)-equol production.

IMPORTANCE

(S)-equol ((S)-EQ) plays a crucial role in maintaining human health, along with its known capacity to prevent and treat various diseases, including cardiovascular diseases, metabolic syndromes, osteoporosis, diabetes, brain-related diseases, high blood pressure, hyperlipidemia, obesity, and inflammation. However, factors affecting individual variations in (S)-EQ production and the underlying regulatory mechanisms remain elusive. This study examines the association between functional genes and (S)-EQ production, highlighting a potential correlation between the DZNR gene and (S)-EQ content. Various types of DZNR may be linked to the regulation of (S)-EQ synthesis. Furthermore, the identification of a new DDRC gene offers promising prospects for enhancing in vitro (S)-EQ production.

Efficient stereoselective hydroxylation of deoxycholic acid by the robust whole-cell cytochrome P450 CYP107D1 biocatalyst

Deoxycholic acid (DCA) has been authorized by the Federal Drug Agency for cosmetic reduction of redundant submental fat. The hydroxylated product (6β-OH DCA) was developed to improve the solubility and pharmaceutic properties of DCA for further applications. Herein, a combinatorial catalytic strategy was applied to construct a powerful Cytochrome P450 biocatalyst (CYP107D1, OleP) to convert DCA to 6β-OH DCA. Firstly, the weak expression of OleP was significantly improved using pRSFDuet-1 plasmid in the E. coli C41 (DE3) strain. Next, the supply of heme was enhanced by the moderate overexpression of crucial genes in the heme biosynthetic pathway. In addition, a new biosensor was developed to select the appropriate redox partner. Furthermore, a cost-effective whole-cell catalytic system was constructed, resulting in the highest reported conversion rate of 6β-OH DCA (from 4.8% to 99.1%). The combinatorial catalytic strategies applied in this study provide an efficient method to synthesize high-value-added hydroxylated compounds by P450s.

Advances in the Metabolic Mechanism and Functional Characteristics of Equol

Equol is the most potent soy isoflavone metabolite and is produced by specific intestinal microorganisms of mammals. It has promising application possibilities for preventing chronic diseases such as cardiovascular disease, breast cancer, and prostate cancer due to its high antioxidant activity and hormone-like activity. Thus, it is of great significance to systematically study the efficient preparation method of equol and its functional activity. This paper elaborates on the metabolic mechanism of equol in humans; focuses on the biological characteristics, synthesis methods, and the currently isolated equol-producing bacteria; and looks forward to its future development and application direction, aiming to provide guidance for the application and promotion of equol in the field of food and health products.

Biosynthesis of (S)-Equol from Soy Whey by Metabolically Engineered Escherichia coli

(S)-Equol is one of the most bioactive metabolites of the isoflavones with immense nutritional and pharmaceutical value. Soy whey is the major liquid byproduct of the soy product processing industries that is rich in nutrients and (S)-equol biosynthetic precursor daidzin. However, it is usually disposed into the sewage, causing high environmental contamination. Herein, we constructed a recombinant Escherichia coli for the biosynthesis of (S)-equol from soy whey. First, we evaluated daidzin-specific transporters and optimized the anaerobically induced P_nar in the (S)-equol biosynthesis cassette to produce (S)-equol from daidzin. Then, sucrase and α-galactosidase were co-expressed to confer sucrose, stachyose, and raffinose utilization capacity on E. coli. Meanwhile, EIIBCA^glc was inactivated to eliminate the daidzin transport inhibition induced by glucose. Finally, combining these strategies and optimizing the fermentation conditions, the optimal strain produced 91.5 mg/L of (S)-equol with a yield of 0.96 mol/mol substrates in concentrated soy whey. Overall, this new strategy is an attractive route to broaden the applications of soy whey and achieve the eco-friendly production of (S)-equol.

Application of cofactors in the regulation of microbial metabolism: A state of the art review

Cofactors are crucial chemicals that maintain cellular redox balance and drive the cell to do synthetic and catabolic reactions. They are involved in practically all enzymatic activities that occur in live cells. It has been a hot research topic in recent years to manage their concentrations and forms in microbial cells by using appropriate techniques to obtain more high-quality target products. In this review, we first summarize the physiological functions of common cofactors, and give a brief overview of common cofactors acetyl coenzyme A, NAD(P)H/NAD(P)+, and ATP/ADP; then we provide a detailed introduction of intracellular cofactor regeneration pathways, review the regulation of cofactor forms and concentrations by molecular biological means, and review the existing regulatory strategies of microbial cellular cofactors and their application progress, to maximize and rapidly direct the metabolic flux to target metabolites. Finally, we speculate on the future of cofactor engineering applications in cell factories. Graphical Abstract.