Control Strategy of Specific Growth Rate in L-Tryptophan Production by Escherichia coli

Abstract

Specific growth rate is an important parameter in L-tryptophan production. In this study, variable specific growth rate fed-batch process was used and the maximum specific growth rate was controlled at 0.20, 0.25, and 0.30 h⁻¹ respectively. The effects of different specific growth rate on dry cell weight, production of L-tryptophan, concentrations of by-products, NH₄ ⁺ and K⁺, and plasmid stability were investigated. With the maximum specific growth rate at 0.25 h⁻¹, dry cell weight increased to 45.37 g/L and L-tryptophan production reached 38.5 g/L. The plasmid stability was 96.2 % and concentration of acetic acid, lactic acid, and alanine was 1.12, 0.72, and 0.45 g/L. From the metabolic flux analysis of L-tryptophan biosynthesis with different specific growth rate, the metabolic flux of Glycolytic pathway, Tricarboxylic acid cycle, acetic acid, lactic acid, and alanine were decreased by 24.18, 17.48, 3.56, 3.34, and 4.0 % respectively and the metabolic flux of Pentose phosphate pathway and L-tryptophan were increased by 8.3 and 5.43 % with the maximum specific growth rate at 0.25 h⁻¹ by comparing with that of the maximum specific growth rate at 0.30 h⁻¹, leading to a significant increase in L-tryptophan production. The maximum specific growth rate in L-tryptophan production should be controlled below 0.25 h⁻¹.