L‐Cysteine Production in Escherichia coli Based on Rational Metabolic Engineering and Modular Strategy

L‐cysteine is an amino acid with important physiological functions and has a wide range of applications in medicine, food, animal feed, and cosmetics industry. In this study, the L‐cysteine synthesis in Escherichia coliEscherichia coli is divided into four modules: the transport module, sulfur module, precursor module, and degradation module. The engineered strain LH03 (overexpression of the feedback‐insensitive cysE and the exporter ydeD in JM109) accumulated 45.8 mg L −1 of L‐cysteine in 48 hr with yield of 0.4% g/g glucose. Further modifications of strains and culture conditions which based on the rational metabolic engineering and modular strategy improved the L‐cysteine biosynthesis significantly. The engineered strain LH06 (with additional overexpression of serA , serC , and serB and double mutant of tnaA and sdaA in LH03) produced 620.9 mg L −1 of L‐cysteine with yield of 6.0% g/g glucose, which increased the production by 12 times and the yield by 14 times more than those of LH03 in the original condition. In fed‐batch fermentation performed in a 5‐L reactor, the concentration of L‐cysteine achieved 5.1 g L −1 in 32 hr. This work demonstrates that the combination of rational metabolic engineering and module strategy is a promising approach for increasing the L‐cysteine production in E. coli .