Improvement of glutathione production by metabolic engineering the sulfate assimilation pathway of Saccharomyces cerevisiae

Glutathione (GSH) is a valuable tri-peptide that is widely used in the pharmaceutical, food, and cosmetic industries. Glutathione is produced industrially by fermentation using Saccharomyces cerevisiae. In this study, we demonstrated that engineering in sulfate assimilation metabolism can significantly improve GSH production. The intracellular GSH content of MET14 and MET16 over-expressing strains increased up to 1.2 and 1.4-fold higher than that of the parental strain, respectively, whereas those of APA1 and MET3 over-expressing strains decreased. Especially, in the MET16 over-expressing strain, the volumetric GSH concentration was up to 1.7-fold higher than that of the parental strain as a result of the synergetic effect of the increases in the cell concentration and the intracellular GSH content. Additionally, combinatorial mutant strains that had been engineered to contain both the sulfur and the GSH synthetic metabolism synergistically increased the GSH production. External addition of cysteine to S. cerevisiae is well known as a way to increase the intracellular GSH content; however, it results a decrease in cell growth. This study showed that the engineering of sulfur metabolism in S. cerevisiae proves more valuable than addition of cysteine as a way to boost GSH production due to the increases in both the intracellular GSH content and the cell growth.