title: Strategy for pH control and pH feedback-controlled substrate feeding for high-level production of L-tryptophan by Escherichia coli.
abstract: Optimum production of L-tryptophan by Escherichia coli depends on pH. Here, we established conditions for optimizing the production of L-tryptophan. The optimum pH range was 6.5-7.2, and pH was controlled using a three-stage strategy [pH 6.5 (0-12 h), pH 6.8 (12-24 h), and pH 7.2 (24-38 h)]. Specifically, ammonium hydroxide was used to adjust pH during the initial 24 h, and potassium hydroxide and ammonium hydroxide (1:2, v/v) were used to adjust pH during 24-38 h. Under these conditions, NH4 (+) and K(+) concentrations were kept below the threshold for inhibiting L-tryptophan production. Optimization was also accomplished using ratios (v/v) of glucose to alkali solutions equal to 4:1 (5-24 h) and 6:1 (24-38 h). The concentration of glucose and the pH were controlled by adjusting the pH automatically. Applying a pH-feedback feeding method, the steady-state concentration of glucose was maintained at approximately 0.2 ± 0.02 g/l, and acetic acid accumulated to a concentration of 1.15 ± 0.03 g/l, and the plasmid stability was 98 ± 0.5 %. The final, optimized concentration of L-tryptophan was 43.65 ± 0.29 g/l from 52.43 ± 0.38 g/l dry cell weight.
authors.affiliation: Key Laboratory of Industrial Microbiology of Education Ministry, College of Biotechnology, Tianjin University of Science and Technology, Tianjin 300457, People's Republic of China.
authors.forename: Li-Kun
authors.initials: LK
authors.lastname: Cheng
authors.forename: Jian
authors.initials: J
authors.lastname: Wang
authors.forename: Qing-Yang
authors.initials: QY
authors.lastname: Xu
authors.forename: Chun-Guang
authors.initials: CG
authors.lastname: Zhao
authors.forename: Zhi-Qiang
authors.initials: ZQ
authors.lastname: Shen
authors.forename: Xi-Xian
authors.initials: XX
authors.lastname: Xie
authors.forename: Ning
authors.initials: N
authors.lastname: Chen
mesh_terms: D064753:Ammonium Hydroxide; D061249:Batch Cell Culture Techniques / Q000379:methods*; D003470:Culture Media / Q000737:chemistry / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism*; D005285:Fermentation; D005947:Glucose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006878:Hydroxides / Q000378:metabolism; D017680:Potassium Compounds / Q000378:metabolism; D014364:Tryptophan / Q000378:metabolism*
chemical_list: D003470:Culture Media; D006878:Hydroxides; D017680:Potassium Compounds; D064753:Ammonium Hydroxide; D014364:Tryptophan; D005947:Glucose; C029943:potassium hydroxide