Effect of Sodium Citrate on L-tryptophan Fermentation by Escherichia coli

Abstract

L-tryptophan is an essential amino acid, and the work for L-tryptophan production by microbial fermentation has important practical significance with the development of L-tryptophan market. In this study, according to the principle of metabolic engineering, the medium of L-tryptophan fermentation by the strain Escherichia coli TRTH was optimized. The accumulation of by-products was decreased and production of desired product was increased by adding sodium citrate to medium. The effect of sodium citrate on L-tryptophan fermentation was investigated in a 30 L fermentor. The results indicated that when L-tryptophan fermentation with the medium containing 2 g/L sodium citrate, as compared with the medium no containing sodium citrate, the biomass, L-tryptophan production and glucose conversion rate were increased by 2.57, 5.32, 4.21 %, and the accumulation of acetate, pyruvate and lactate were decreased by 5.15, 4.89, 5.23 %. With the medium containing 2 g/L sodium citrate for L-tryptophan fermentation, the biomass, L-tryptophan production and glucose conversion rate were 42.7, 35.7 and 18.2 % respectively.