Wang Chenyang, Li Qinyu, Zhou Peng, Chen Xiaojia, Shi Jiping, Zhao Zhijun
Biorefinery Laboratory, Shanghai Advanced Research Institute, Chinese Academy of Sciences, 99 Haike Road, Shanghai 201210, China.
College of Life Sciences, University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing 100049, China.
Microorganisms. 2022 Sep 28;10(10):1927. doi: 10.3390/microorganisms10101927.
L-serine is widely used in the food, cosmetic, and pharmaceutical industries. However, the complicated metabolic network and regulatory mechanism of L-serine production lead to the suboptimal productivity of the direct fermentation of L-serine and limits its large-scale industrial production. In this study, a high-yield L-serine production strain was constructed by a series of defined genetic modification methodologies. First, L-serine-mediated feedback inhibition was removed and L-serine biosynthetic pathway genes (, , and ) associated with phosphoglycerate kinase () were overexpressed. Second, the L-serine conversion pathway was further examined by introducing a mutation (K229G) and deleting other degrading enzymes based on the deletion of initial . Finally, the L-serine transport system was rationally engineered to reduce uptake and accelerate L-serine export. The optimally engineered strain produced 35 g/L L-serine with a productivity of 0.98 g/L/h and a yield of 0.42 g/g glucose in a 5-L fermenter, the highest productivity and yield of L-serine from glucose reported to date. Furthermore, transcriptome and intermediate metabolite of the high-yield L-serine production strain were analyzed. The results demonstrated the regulatory mechanism of L-serine production is delicate, and that combined metabolic and bioprocess engineering strategies for L-serine producing strains can improve the productivity and yield.
L-丝氨酸广泛应用于食品、化妆品和制药行业。然而，L-丝氨酸生产复杂的代谢网络和调控机制导致L-丝氨酸直接发酵的生产力欠佳，并限制了其大规模工业化生产。在本研究中，通过一系列明确的基因改造方法构建了一株高产L-丝氨酸的菌株。首先，消除L-丝氨酸介导的反馈抑制，并过表达与磷酸甘油酸激酶（PGK）相关的L-丝氨酸生物合成途径基因（PSPH、SERB和SERC）。其次，通过引入aldhA突变（K229G）并在删除初始aldhA的基础上删除其他降解酶，进一步研究L-丝氨酸转化途径。最后，对L-丝氨酸转运系统进行合理改造，以减少摄取并加速L-丝氨酸输出。经过优化改造的菌株在5-L发酵罐中产生了35 g/L的L-丝氨酸，生产力为0.98 g/L/h，葡萄糖产率为0.42 g/g，这是迄今为止报道的葡萄糖产生L-丝氨酸的最高生产力和产率。此外，还对高产L-丝氨酸菌株的转录组和中间代谢产物进行了分析。结果表明，L-丝氨酸生产调控机制精细，且针对L-丝氨酸生产菌株的代谢与生物过程工程相结合的策略可以提高生产力和产率。
