Metabolic engineering of Corynebacterium glutamicum for l-cysteine production

l-cysteine, a valuable sulfur-containing amino acid, has been widely used in food, agriculture, and pharmaceutical industries. Due to the toxicity and complex regulation of l-cysteine, no efficient cell factory has yet been achieved for l-cysteine industrial production. In this study, the food-grade microorganism Corynebacterium glutamicum was engineered for l-cysteine production. Through deletion of the l-cysteine desulfhydrases (CD) and overexpression of the native serine acetyltransferase (CysE), the initial l-cysteine-producing strain CYS-2 was constructed to produce 58.2 ± 5.1 mg/L of l-cysteine. Subsequently, several metabolic engineering strategies were performed to further promote l-cysteine biosynthesis, including using strong promoter tac-M to enhance expression intensity of CysE, investigating the best candidate among several heterogeneous feedback-insensitive CysEs for l-cysteine biosynthesis, overexpressing l-cysteine synthase (CysK) to drive more metabolic flux, evaluating the efflux capacity of several heterogeneous l-cysteine transporters, engineering l-serine biosynthesis module to increase the precursor l-serine level and using thiosulfate as the sulfur source. Finally, the l-cysteine concentration of the engineered strain CYS-19 could produce 947.9 ± 46.5 mg/L with addition of 6 g/L Na2S2O3, approximately 14.1-fold higher than that of the initial strain CYS-2, which was the highest titer of l-cysteine ever reported in C. glutamicum. These results indicated that C. glutamicum was a promising platform for l-cysteine production.