Improving glutathione production by engineered Pichia pastoris: strain construction and optimal precursor feeding.

Glutathione (GSH) is a metabolite that plays an important role in the fields of pharmacy, food, and cosmetics. Thus, it is necessary to increase its production to meet the demands. In this study, ScGSH1, ScGSH2, and StGshF were heterologously expressed in Pichia pastoris GS115 to realize the dual-path synthesis of GSH in yeast. To explore the effects of ATP metabolism on the synthesis of GSH, enzymes (ScADK1, PpADK1, VsVHB) of the ATP-related metabolic pathway and the energy co-substrate sodium citrate were taken into account. We found that both ScADK1 and sodium citrate had a positive influence on the synthesis of GSH. Then, a fermentation experiment in Erlenmeyer flasks was performed using the G3-SF strain (containing ScGSH1, ScGSH2, StGshF, and ScADK1), with the highest GSH titer and yield of 999.33 ± 47.26 mg/L and 91.53 ± 4.70 mg/g, respectively. Finally, the fermentation was scaled up in a 5-L fermentor, and the highest titer and yield were improved to 5680 mg/L and 45.13 mg/g, respectively, by optimizing the addition conditions of amino acids (40 mM added after 40 h). Our work provides an alternative strategy by combining dual-path synthesis with energy metabolism regulation and precursor feeding to improve GSH production. Key Points • ScGSH1, ScGSH2, and StGshF were overexpressed to achieve dual-path synthesis of GSH in yeast. • ScADK1 was overexpressed, and sodium citrate was added to increase the energy supply for GSH synthesis. • The addition conditions of amino acids were optimized to realize the efficient synthesis of GSH.