Enzymatic synthesis of L-cysteine by Escherichia coli whole-cell biocatalyst

Abstract

L-cysteine, a sulfur-containing amino acid with important physiological function, is usually extracted from hydrolyzed protein. In this study, we focused on a biocatalytic process with Escherichia coli whole-cell biocatalyst for the production of l-cysteine. The genes encoding l-2-amino-Δ2-thiazoline-4-carboxylic acid (l-ATC) hydrolase (atcB) and N-carbamoyl-l-cysteine (l-NCC) amidohydrolase (atcC) were synthesized and expressed in E. coli BL21. The recombinant E. coli strain was used as the whole-cell biocatalyst to convert dl-ATC, and 13.1 mM of l-cysteine was accumulated. Deletion of the l-cysteine desulfhydrase gene tnaA in E. coli BL21 resulted in a further 54.4% increase of l-cysteine production. The optimal pH and temperature of l-cysteine production were 7.0 and 37 °C, respectively. In addition, we also explored the effects of glycerol concentration on the accumulation of l-cysteine. It shows that the optimal glycerol concentration was 10%. Finally, 70.2 mM of l-cysteine was accumulated at 8 h under optimum conditions.