Identifying and overcoming the limitations preventing efficient high-yield production of chemicals remain important tasks in metabolic engineering. In an attempt to rewire Corynebacterium glutamicum to produce ethanol, we attained a low yield (63% of the theoretical) when using resting cells on glucose, and large amounts of succinate and acetate were formed. To prevent the by-product formation, we knocked out the malate dehydrogenase and replaced the native E3 subunit of the pyruvate dehydrogenase complex (PDHc) with that from Escherichia coli, which is active only under aerobic conditions. However, this tampering resulted in a 10-times-reduced glycolytic flux as well as a greatly increased NADH/NAD⁺ ratio. When we replaced glucose with fructose, we found that the glycolytic flux was greatly enhanced, which led us to speculate whether the source of reducing power could be the pentose phosphate pathway (PPP) that is bypassed when fructose is metabolized. Indeed, after shutting down the PPP by deleting the zwf gene, encoding glucose-6-phosphate dehydrogenase, the ethanol yield on glucose increased significantly, to 92% of the theoretical. Based on that, we managed to rechannel the metabolism of C. glutamicum into d-lactate with high yield, 98%, which is the highest that has been reported. It is further demonstrated that the PPP-inactivated platform strain can offer high-yield production of valuable chemicals using lactose contained in dairy waste as feedstock, which paves a promising way for potentially turning dairy waste into a valuable product.

中文翻译：

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氧化戊糖磷酸途径的破坏刺激了使用谷氨酸棒杆菌在没有外部电子受体的情况下的高产生产。

识别并克服阻碍高效高效生产化学品的局限性仍然是代谢工程中的重要任务。为了使谷氨酸棒杆菌重新连接以生产乙醇，当在葡萄糖上使用静置细胞时，我们获得了较低的收率（理论值的63％），并形成了大量的琥珀酸盐和乙酸盐。为了防止副产物的形成，我们敲除了苹果酸脱氢酶，并用大肠杆菌的丙酮酸脱氢酶复合物（PDHc）的天然E3亚基代替了大肠杆菌，仅在有氧条件下才有活性。但是，这种篡改导致糖酵解通量降低了10倍，并且NADH / NAD ⁺比。当我们用果糖代替葡萄糖时，我们发现糖酵解通量得到了极大的增强，这使我们推测还原能力的来源是否可能是果糖代谢时绕过的戊糖磷酸途径（PPP）。实际上，在通过删除编码6磷酸葡萄糖脱氢酶的zwf基因而关闭PPP之后，葡萄糖的乙醇收率显着提高，达到理论值的92％。在此基础上，我们成功地rechannel的代谢谷氨酸为d-乳酸产量高，达98％，这是最高的报道。进一步证明，使用乳制品废料中所含的乳糖作为原料，PPP灭活的平台菌株可以提供高产有价值的化学药品，这为将乳制品废料转化为有价值的产品铺平了前途。