Abstract: Escherichia coli BL21(DE3) strains that can overproduce methionine were constructed by regulating the methionine biosynthesis pathway. Knocking out metJ, a gene encoding the methionine biosynthesis repressor, demonstrated the initial accumulation of methionine (22 mg/L) by E. coli BL21(DE3). L-methionine yield was then increased to 60 mg/L by selection of methionine analogue resistant YB12 using the ultraviolet mutagenesis. Furthermore, over-expression of methionine biosynthesis key genes metA, cysE and yeaS in YB12 dramatically enhanced the production of methionine by E. coli strains (251 mg/L). These results indicated that the combination of gene modification and gene regulation in methionine biosynthesis pathway was required to achieve the high accumulation of methionine or the construction of met-excreting strains.

Key words: Escherichia coli, methionine, mutagenesis, metJ, over-expression

摘要： 以Escherichia coli BL21(DE3)为出发菌株，敲除其蛋氨酸合成途径中关键酶的阻遏基因metJ，使菌株积累蛋氨酸达22 mg/L. 在此基础上，利用紫外诱变筛选育出一株抗蛋氨酸结构类似物的蛋氨酸高产菌株YB12，使蛋氨酸产量提高到60 mg/L. 通过过量表达蛋氨酸合成途径中的metA和cysE基因及编码蛋氨酸转运蛋白的yeaS基因，YB12菌株积累蛋氨酸量提高到251 mg/L. 结果表明，蛋氨酸在胞外的积累受多个基因、多种代谢途径调控，单独敲除某个基因或改造某个途径不能使蛋氨酸大量合成和积累，对多个代谢途径共同改造是构建蛋氨酸工程菌的最有效方法.

关键词: 大肠杆菌, 蛋氨酸, 突变, metJ, 过量表达