Effect of gene knockouts of l-tryptophan uptake system on the production of l-tryptophan in Escherichia coli

Uptake of l-tryptophan in Escherichia coli was carried out by three distinct permeases, Mtr, TnaB, and AroP, respectively. In the present study, the three genes of l-tryptophan uptake system were knocked out from an l-tryptophan-producing strain of E. coli, respectively. The knockout mutants all showed lower l-tryptophan uptake activities and higher l-tryptophan production than their parent. Among the three genes, the knockout of mtr was most critical for both l-tryptophan uptake and l-tryptophan production. The uptake activity of l-tryptophan of the mtr mutant was 1.5 nmol min−1 (mg dry weight)−1, which was decreased by 48% when compared to that of the parent; the production of l-tryptophan of the mtr mutant was 14.7 g/l, which was increased by 34% when compared to that of the parent. Furthermore, the physiological and fermentation characteristics caused by gene knockouts were also analyzed.

► The knockout mutants of mtr, tnaB, and aroP were, respectively, constructed.
► The mutants all showed lower l-Trp uptake activities than their parent.
► The mutants all showed higher l-Trp production than their parent.
► The knockout of mtr was most critical for both l-Trp uptake and l-Trp production.
► The prevention of l-Trp uptake may be a useful strategy for l-Trp production.