L-苏氨酸是人类必需氨基酸，在医药、食品、饲料领域有广泛的应用。在L-苏氨酸发酵生产过程中,乙醛酸循环起到部分回补途径的功能。本实验利用Red重组技术，以L-苏氨酸生产菌Escherichia coli THRD 为出发菌株，构建了iclR基因缺失菌株THRD ΔiclR以及不同强度启动子替换aceBAK启动子的菌株THRD P1和THRD P2。通过实时荧光定量PCR检测表明，苹果酸合酶基因（aceB）的表达量分别是原菌的1.89倍、2.11倍以及2.96倍。摇瓶发酵结果显示，THRD ΔiclR的L-苏氨酸产量及糖酸转化率分别为42.60±1.23 g/L和32.77 g/g，较原菌THRD（35.32±1.07 g/L和27.17 g/g）分别提高20.61%和20.70%。THRD P1 L-苏氨酸产量及糖酸转化率分别为36.50±1.42 g/L和28.08 g/g，较原菌THRD（35.32±1.07 g/L和27.17 g/g）分别提高3.34%和3.39%。而THRD P2 8 h后菌体生长停滞，L-苏氨酸产量及糖酸转化率分别为8.31±1.31 g/L和20.78 g/g，较原菌THRD（35.32±1.07 g/L和27.17 g/g）分别降低了76.47%和23.52%。综上所述，适当增强乙醛酸循环有利于L-苏氨酸的积累，而过强的乙醛酸循环影响菌体的正常代谢。

Abstract:

L-threonine, an essential amino acid, is widely used in the agricultural, pharmaceutical, and cosmetic industries. In the L-threonine fermentation process, the glyoxylate cycle functions as part of the feedback pathway. In this work, Escherichia coli THRD that can produce L-threonine were used as original strains. Red reconstruction technology was used to construct a strain lacking iclR (Escherichia coli THRD ΔiclR) and THRD P1 and THRD P2, in which aceBAK promoter in E. coli THRD was replaced by promoters of various strength.. Fluorescent quantitative real-time PCR analysis showed that the expression of the aceB gene in the different strains was upregulated by 1.89-, 2.11-, and 2.96-fold, respectively, compared with the original strain. The results from fermentation in shaken flasks showed that the L-threonine and sugar-acid conversion rate of E. coli THRD ΔiclR were 42.60±1.23 g/L and 32.77 g/g, respectively, which were 20.61% and 20.7% higher than those of the control strain THRD (35.32±1.07 g/L and 27.17 g/g). The L-threonine and sugar-acid conversion rate of E. coli THRD P1 were 36.50±1.42 g/L and 28.08 g/g, which increased by 3.34% and 3.39% from those obtained from the control strain, respectively. However, E. coli THRD P2 stopped growing after 8 h and resulted in L-threonine production of 8.31±1.31 g/L and a sugar-acid conversion rate of 20.78 g/, which were 76.47% and 23.52%, respectively, lower than those of the control strain THRD. In conclusion, moderate enhancement of the glyoxylate cycle benefited L-threonine accumulation, while excessive enhancement of glyoxylate cycle had a negative effect on the normal cell metabolism.