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. (C) 2011 Elsevier Ltd. All rights reserved.