Heterologous gshF gene expression in various vector systems in Escherichia coli for enhanced glutathione production

Glutathione (GSH), an important bioactive product, is widely used in production of pharmaceuticals and foods. In this study, four different vector systems, pET28a, pUC18, pUC19-P32, and pUC19-Pabb, were applied for expression of gshF, encoding the bifunctional glutathione synthetase of Streptococcus thermophiles. These four constructs were named as pET28a-gshF, pUC18-gshF, pUC19-P32-gshF and pUC19-Pabb-gshF, respectively, and then introduced into Escherichia coli strain BL21(DE3) for further investigation of protein expression and GSH production. The expression levels of the GshF in BL21(pUC19-P32-gshF) and BL21(pUC19-Pabb-gshF) were much lower than those of BL21(pET28a-gshF) and BL21(pUC18-gshF). In the fed-batch fermentation, the GSH accumulated by BL21(pUC18-gshF) reached 15.21 g/L, which was the highest level of GSH biosynthesis ever reported. Although BL21(pUC19-Pabb-gshF) produced less GSH compared to BL21(pUC18-gshF), the final GSH concentration produced by BL21 (pUC19-Pabb-gshF) still accumulated to 5.09 g/L, which indicated the potential application of the constitutive promoter in GSH production.