Fermentation characterization of an L-tryptophan producing Escherichia coli strain with inactivated phosphotransacetylase

Abstract

Acetate is a primary inhibitory metabolite in Escherichia coli cultivation which is detrimental to bacterial growth and the formation of desired products. It can be derived from acetyl coenzyme A by the phosphotransacetylase (Pta)–acetate kinase (AckA) pathway. In this study, the fermentation characteristics of Pta mutant strain E. coli TRTHΔpta were compared with those of the control strain E. coli TRTH in a 30-L fermentor. The effects of glucose concentration and dissolved oxygen (DO) level were investigated, and the results suggest that DO and glucose concentration are vital influencing parameters for the production of L-tryptophan. Based on our experimental results, we then tested a DO-stat fed-batch fermentation strategy. When DO was controlled at about 20 % during L-tryptophan fermentation in the DO-stat fed-batch system, the pta mutant was able to maintain a higher growth rate at the exponential phase, and the final biomass and L-tryptophan production were increased to 55.3 g/L and 35.2 g/L, respectively. Concomitantly, as the concentration of acetate decreased to 0.7 g/L, the accumulation of pyruvate and lactate increased in the mutant strain as compared with the control strain. This characterization of the recombinant mutant strain provides useful information for the rational modification of metabolic fluxes to improve tryptophan production.