Laboratory of Pharmaceutical Engineering, School of Pharmaceutics Science, Jiangnan University, Wuxi, 214122, China.
The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, 214122, China.
Biotechnol J. 2019 Jun;14(6):e1800497. doi: 10.1002/biot.201800497. Epub 2019 May 20.
l-Serine is widely used in the pharmaceutical, food, and cosmetic industries. The direct fermentative production of l-serine from glucose in Corynebacterium glutamicum (C. glutamicum) has been achieved but the yield is generally low. In this study, the central metabolic pathway is rewired to direct higher accumulation of glycerate-3-phosphate (3-PG), the precursor for l-serine biosynthesis, thereby freeing up more carbon to enhance l-serine production and yield. To this end, the native phosphotransferase system (PTS) is inactivated by deleting the gene ptsH. Meanwhile, the PTS-independent glucose uptake pathway is activated via overexpression of iolT1, ppgk, and deletion of the transcriptional regulator gene iolR. Furthermore, metabolic changes between PTS and non-PTS strains are elucidated using gas chromatography-tandem mass spectrometry. Based on the metabonomic and enzyme activities analysis, the glycolysis pathway upstream of 3-PG is further enhanced by co-overexpressing pgi, pfkA, and gapA. The resulting strain with all of the modifications mentioned above leads to the l-serine yield of 0.30 g g glucose (42.8% higher than that of the original strain), which is the highest yield in C. glutamicum by using glucose as the sole carbon source. These strategies can be expanded for the production of other value-added chemicals derived from the intermediates of glycolysis pathway in C. glutamicum.
l-丝氨酸被广泛应用于医药、食品和化妆品行业。利用谷氨酸棒杆菌（Corynebacterium glutamicum）直接从葡萄糖发酵生产 l-丝氨酸已经实现，但产量普遍较低。在这项研究中，通过敲除 ptsH 基因，使中央代谢途径重新布线，从而直接增加甘油-3-磷酸（3-PG）的积累，3-PG 是 l-丝氨酸生物合成的前体，从而释放更多的碳来提高 l-丝氨酸的产量和产率。为此，通过过表达 iolT1、ppgk 并敲除转录调节基因 iolR，使原本依赖磷酸转移酶系统（PTS）的葡萄糖摄取途径被激活。此外，还通过气相色谱-串联质谱法阐明了 PTS 和非 PTS 菌株之间的代谢变化。基于代谢组学和酶活分析，通过共过表达 pgi、pfkA 和 gapA 进一步增强了 3-PG 上游的糖酵解途径。经过上述所有修饰的菌株，以葡萄糖为唯一碳源时，l-丝氨酸的产量达到 0.30 g g 葡萄糖（比原始菌株提高了 42.8%），这是谷氨酸棒杆菌利用葡萄糖生产 l-丝氨酸的最高产量。这些策略可以扩展到利用谷氨酸棒杆菌糖酵解途径中间产物生产其他有价值的化学品。
