To improve the S-adenosylmethionine (SAM) production in methionine-free medium, effects of deleting genes of SAM decarboxylase (speD) and homoserine kinase (thrB) on SAM titers were investigated, and the SAM synthetase gene (SAM2) was also overexpressed. In B. amyloliquefaciens HSAM2, deleting speD to block the SAM utilization pathway significantly reduced the SAM titer. After knockout of thrB to block the branched pathway, the resulted mutant HSAM4 produced 143.93 mg/L SAM, increasing by 42% than HSAM2. Further plasmid-based expression of SAM2 improved the SAM titer to 226.92 mg/L, and final optimization of key fermentation parameters resulted in the maximum SAM titer of 412.01 mg/L in flasks batch fermentation. Deleting thrB and overexpressing SAM2 gene were efficient for enhanced SAM production in B. amyloliquefaciens. The maximum SAM titer in flasks batch fermentation was much higher than that of previous reports.

中文翻译：

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通过删除 thrB 基因和过表达 SAM2 基因在解淀粉芽孢杆菌中增强 S-腺苷甲硫氨酸的产生

为了提高无蛋氨酸培养基中 S-腺苷甲硫氨酸 (SAM) 的产量，研究了删除 SAM 脱羧酶 (speD) 和高丝氨酸激酶 (thrB) 基因对 SAM 滴度的影响，并且还过表达了 SAM 合成酶基因 (SAM2)。在解淀粉芽孢杆菌 HSAM2 中，删除 speD 以阻断 SAM 利用途径显着降低了 SAM 滴度。在敲除 thrB 以阻断分支途径后，所得突变体 HSAM4 产生 143.93 mg/L SAM，比 HSAM2 增加 42%。进一步基于质粒的 SAM2 表达将 SAM 滴度提高到 226.92 mg/L，关键发酵参数的最终优化导致烧瓶分批发酵中的最大 SAM 滴度为 412.01 mg/L。删除 thrB 和过表达 SAM2 基因对于提高解淀粉芽孢杆菌中的 SAM 生产是有效的。