Control Strategy of Specific Growth Rate in L-Tryptophan Production by Escherichia coli
Specific growth rate is an important parameter in L-tryptophan production. In this study, variable specific growth rate fed-batch process was used and the maximum specific growth rate was controlled at 0.20, 0.25, and 0.30 h−1 respectively. The effects of
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Control Strategy of Specific Growth Rate in L-Tryptophan Production by Escherichia coli Likun Cheng, Qingyang Xu, Jingbo Liang, Xixian Xie, Chenglin Zhang and Ning Chen
Abstract Specific growth rate is an important parameter in L-tryptophan production. In this study, variable specific growth rate fed-batch process was used and the maximum specific growth rate was controlled at 0.20, 0.25, and 0.30 h-1 respectively. The effects of different specific growth rate on dry cell weight, production of L-tryptophan, concentrations of by-products, NH4+ and K+, and plasmid stability were investigated. With the maximum specific growth rate at 0.25 h-1, dry cell weight increased to 45.37 g/L and L-tryptophan production reached 38.5 g/L. The plasmid stability was 96.2 % and concentration of acetic acid, lactic acid, and alanine was 1.12, 0.72, and 0.45 g/L. From the metabolic flux analysis of L-tryptophan biosynthesis with different specific growth rate, the metabolic flux of Glycolytic pathway, Tricarboxylic acid cycle, acetic acid, lactic acid, and alanine were decreased by 24.18, 17.48, 3.56, 3.34, and 4.0 % respectively and the metabolic flux of Pentose phosphate pathway and L-tryptophan were increased by 8.3 and 5.43 % with the maximum specific growth rate at 0.25 h-1 by comparing with that of the maximum specific growth rate at 0.30 h-1, leading to a significant increase in L-tryptophan production. The maximum specific growth rate in L-tryptophan production should be controlled below 0.25 h-1.
Keywords Specific growth rate L-tryptophan Escherichia coli By-products Metabolic flux analysis
L. Cheng Q. Xu J. Liang X. Xie C. Zhang N. Chen (&) College of Biotechnology, Tianjin University of Science and Technology, Tianjin 300457, China e-mail: [email protected]
T.-C. Zhang et al. (eds.), Proceedings of the 2012 International Conference on Applied Biotechnology (ICAB 2012), Lecture Notes in Electrical Engineering 249, DOI: 10.1007/978-3-642-37916-1_25, Ó Springer-Verlag Berlin Heidelberg 2014
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25.1 Introduction L-tryptophan is an essential amino acid for humans and other animals, which is widely used in food, animal feed, and pharmaceutical industries [1, 2]. Process modification and genetic modification of L-tryptophan production by microbial fermentation in E. coli has been extensively studied [3, 4]. Zhao et al. constructed an L-tryptophan overproducing E. coli (DTrpR, DTnaA, DPheA, DTyrA, AroFfbr and TrpEfbrD) from the wild-type E. coli W3110 by defined genetic modification methodology [2]. In L-tryptophan production, product formation increased, and the amount of by-products decreased by optimizing the glucose feed rate [1]. Specific growth rate is an important parameter in the fermentation process due to its impact on the plasmid stability and the formation of acetic acid [5]. Plasmid stability decreased with rise in specific growth rate and plasmid instability is a major reason for the decrease in the specific yield [6]. Acetic acid is a primary inhibitory metabolite
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