Phage infection is common during the production of L-threonine by E. coli, and low L-threonine production and glucose conversion percentage are bottlenecks for the efficient commercial production of L-threonine. In this study, 20 antiphage mutants producing high concentration of L-threonine were obtained by atmospheric and room temperature plasma (ARTP) mutagenesis, and an antiphage E. coli variant was characterized that exhibited the highest production of L-threonine Escherichia coli ([E. coli] TRFC-AP). The elimination of fhuA expression in E. coli TRFC-AP was responsible for phage resistance. The biomass and cell growth of E. coli TRFC-AP showed no significant differences from those of the parent strain (E. coli TRFC), and the production of L-threonine (159.3 g L −1) and glucose conversion percentage (51.4%) were increased by 10.9% and 9.1%, respectively, compared with those of E. coli TRFC. During threonine production (culture time of 20 h), E. coli TRFC-AP exhibited higher activities of key enzymes for glucose utilization (hexokinase, glucose phosphate dehydrogenase, phosphofructokinase, phosphoenolpyruvate carboxylase, and PYK) and threonine synthesis (glutamate synthase, aspartokinase, homoserine dehydrogenase, homoserine kinase and threonine synthase) compared to those of E. coli TRFC. The analysis of metabolic flux distribution indicated that the flux of threonine with E. coli TRFC-AP reached 69.8%, an increase of 16.0% compared with that of E. coli TRFC. Overall, higher L-threonine production and glucose conversion percentage were obtained with E. coli TRFC-AP due to increased activities of key enzymes and improved carbon flux for threonine synthesis.

In this study, process engineering and process control were applied to increase the production of l‐tryptophan using Escherichia coli Dmtr/pta‐Y. Different dissolved oxygen (DO) and pH control strategies were applied in l‐tryptophan production. DO and pH were maintained at [20% (0–20 hr); 30% (20–40 hr)] and [7.0 (0–20 hr), 6.5 (20–40 hr)], respectively, which increased l‐tryptophan production, glucose conversion percentage [g (l‐tryptophan)/g (glucose)], and transcription levels of key genes for tryptophan biosynthesis and tryptophan biosynthesis flux, and decreased the accumulation of acetate and transcription levels of genes related to acetate synthesis and acetate synthesis flux. Using E. coli Dmtr/pta‐Y with optimized DO [20% (0–20 hr); 30% (20–40 hr)] and pH [7.0 (0–20 hr), 6.5 (20–40 hr)] values, the highest l‐tryptophan production (52.57 g/L) and glucose conversion percentage (20.15%) were obtained. The l‐tryptophan production was increased by 26.58%, the glucose conversion percentage was increased by 22.64%, and the flux of tryptophan biosynthesis was increased to 21.5% compared with different conditions for DO [50% (0–20 hr), 20% (20–40 hr)] and pH [7.0].

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