Engineering Escherichia coli for Ergothioneine Production via Metabolic Engineering and Fermentation Optimization

Ergothioneine (EGT), a naturally occurring amino acid derivative with potent antioxidant and cytoprotective properties, is widely applied in the food, cosmetic, and medical industries. Traditional production methods are limited by high costs, low efficiency, and environmental concerns, so microbial fermentation serves as a sustainable alternative for EGT production. In this study, Escherichia coli BL21 (DE3) was employed as the chassis strain. First, a basic EGT-producing engineered strain was constructed by heterologously expressing the egtB gene from Methylobacterium pseudosasicola along with the egtD and egtE genes from Mycobacterium smegmatis. This initial strain achieved a yield of 84.84 ± 1.64 mg/L of EGT in shake-flask cultures. To enhance production, solubility-enhancing tags were introduced to improve the soluble expression of the key enzymes, and metabolic pathways were rationally engineered to strengthen the supply of essential precursor amino acids. These modifications led to the development of a high-yield EGT strain. After optimizing the fermentation process, the best results were achieved using a medium with glycerol as the carbon source, 0.5 g/L of histidine, 1.5 g/L of methionine, and 1.0 g/L of cysteine, along with induction at 25 °C using 0.2 mM IPTG for 120 h. Under these conditions, the final EGT yield reached 385.70 ± 4.86 mg/L. The engineered strain for EGT synthesis and optimized fermentation strategy developed in this study offer a useful basis for further process development.