Efficient glutathione production in metabolically engineered Escherichia coli strains using constitutive promoters

Glutathione (GSH) is an important bioactive tripeptide and widely used in food, medicine and other industries. Recently, the bifunctional glutathione synthetase, GshF, has been applied for efficient GSH production under inducible promoter. In this study, the constitutive expression of GshF from Streptococcus sanguinis (GshFss) was investigated under four different constitutive promoters. Based on previous study, five genes in Escherichia coli JM109 were deleted to eliminate the degradation of precursors and GSH. The effects of gene knockout on the constitutive expression of GshFss and GSH production were evaluated by whole cell catalysis. Finally, the engineered strain JM03P^del1 produced 24 mM glutathione with addition of 30 mM precursors in 5-L bioreactor fed-batch fermentation. The yield of GSH based on cysteine in JM03P^del1was reached 80% without any inducer, which was improved by 17.3% than that in the control strain.