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Enhanced L-methionine production by genetically engineered Escherichia coli through fermentation optimization

Zhou, Hai-Yan, Wu, Wang-Jie, Niu, Kun, Xu, Yue-Ying, Liu, Zhi-Qiang, Zheng, Yu-Guo
3 Biotech 2019 v.9 no.3 pp. 96
Escherichia coli, agitation, batch fermentation, biosynthesis, culture media, experimental design, fermenters, genetic engineering, glucose, pH, potassium dihydrogen phosphate, temperature, yeast extract
Microbial fermentation for L-methionine (L-Met) production based on natural renewable resources is attractive and challenging. In this work, the effects of medium composition and fermentation conditions were investigated to improve L-Met production by genetically engineered Escherichia coli MET-3. Statistical optimization techniques including Plackett–Burman (PB) design and Box–Behnken design (BBD) were adopted first to optimize the culture medium. Results of PB-designed experiments indicated that the culture medium components including glucose, yeast extract, KH₂PO₄, and MgSO₄.7H₂O had significant effects on L-Met biosynthesis. With their best-predicted concentration established by BBD (glucose 37.43 g/L, yeast extract 0.95 g/L, KH₂PO₄ 1.82 g/L, and MgSO₄.7H₂O 4.51 g/L), L-Met titer was increased to 3.04 g/L from less than 2.0 g/L. For further enhancement of L-Met biosynthesis, the fermentation conditions of batch cultivation carried out in a 5-L fermentor were optimized, and the optimum results were obtained at an agitation rate of 300 rpm, medium pH of 7.0, and induction temperature of 28 °C. Based on the optimization parameters, fed-batch fermentation with the modified medium was conducted. As a result, great improvement of L-Met titer (12.80 g/L) and yield (0.13 mol/mol) were achieved, with an increase of 38.53% and 30.0% compared with those of the basal medium, respectively. Furthermore, higher L-Met productivity of 0.261 g/L/h was obtained, representing 2.13-fold higher in comparison to the original medium. The results may provide a helpful reference for further study on strain improvement and fermentation control.