Impact of deletion of the genes encoding acetate kinase on production of L-tryptophan by Escherichia coli

Abstract

The production of L-tryptophan was increased by reducing acetate accumulation through a decrease in acetate kinase activity by gene deletion. The effects of disruption of the genes for acetate kinase (ackA) and an enzyme with propionate/acetate kinase activity (tdcD) on L-tryptophan production were investigated. The ackA and/or tdcD deletion mutants accumulated less acetate and more L-tryptophan than the parental strain. Furthermore, the production of L-tryptophan obtained with ackA-tdcD mutant were more than the mutants with a single deletion of ackA or tdcD, while higher production of L-tryptophan and lower concentration of acetate were accumulated in the ackA mutant than the mutant with a lesion in tdcD. In L-tryptophan fed-batch fermentation using the ackA-tdcD mutant, the excretion of acetate was reduced to 1.22 g/L, a 21.79 % reduction compared with the parental strain, and the production of L-tryptophan and glucose conversion rate were increased to 52.5 g/L and 47.9 g/L, respectively, which represented 6.49 % and 10.88 % increases compared with the parental strain, and the glucose conversion rate reached a high level of 21.2 %, which was 8.16 % higher than the parental strain. In addition, the metabolic flux analysis of TRTH and TRTHAT indicated that the carbon flux through EMP was decreased by 8.37 % and the carbon flux through PP was increased by 57.03 % in TRTHAT compared with TRTH. The flux of acetate and tryptophan formation of TRTHAT were 5.2 % and 17.3 %, which were 3.67-times lower and 1.75-times higher than these of TRTH, respectively.