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Gene modification of Escherichia coli and incorporation of process control to decrease acetate accumulation and increase ʟ-tryptophan production

Lu, Na, Zhang, Bin, Cheng, Likun, Wang, Jinshui, Zhang, Songlin, Fu, Shijun, Xiao, Yueqiang, Liu, Hongyan
Annals of microbiology 2017 v.67 no.8 pp. 567-576
Escherichia coli, acetates, biomass production, byproducts, dissolved oxygen, fermentation, genes, genetic engineering, glucose, industrialization, metabolites, mutants, pH, phosphates, process control, tryptophan
Acetate is a primary inhibitory metabolite in cultures of Escherichia coli, and the production of both biomass and desired products are increased by reducing the accumulation of acetate. In this study, the accumulation of acetate during ʟ-tryptophan production was decreased by genetic modification of ʟ-tryptophan-producing strain (BCTRP) and optimization of the fermentation process. The mutant (BCTRPG), which has a deletion of the integral membrane permease IICBᴳˡᶜ (ptsG), produces a higher concentration of ʟ-tryptophan than mutants with deletions of either phosphate acetyltransferase (pta) or pta–ptsG, due to the low accumulation of acetate and other byproducts, as well as high biomass production. The appropriate dissolved oxygen (DO) level, glucose feeding mode, and pH control strategy were applied to ʟ-tryptophan production using the BCTRPG mutant. The BCTRPG strain with optimized conditions resulted in a reduction in acetate accumulation (71.08% reduction to 0.72 g/L) and an increase in ʟ-tryptophan production (35.81% increase to 17.14 g/L) compared with the BCTRP strain in the original culture condition. Meanwhile, an analysis of the metabolic flux distribution indicated that the acetate synthesis flux decreased from 19.2% (original conditions) to 8.4% (optimized conditions), and the flux of tryptophan formation with the optimized conditions was 18.5%, which was 1.89 times higher than under the original conditions. This study provided the theoretical foundation and technical support for high-level industrialization production of ʟ-tryptophan.