Reducing lactate secretion by ldhA Deletion in L-glutamate- producing strain Corynebacterium glutamicum GDK-9

Zhang, DalongGuan, DanLiang, JingboGuo, ChunqianXie, XixianZhang, ChenglinXu, QingyangChen, Ning

L-lactate is one of main byproducts excreted in to the fermentation medium. To improve L-glutamate production and reduce L-lactate accumulation, L-lactate dehydrogenase-encoding gene ldhA was knocked out from L-glutamate producing strain Corynebacterium glutamicum GDK-9, designated GDK-9ldhA. GDK-9ldhA produced approximately 10.1% more L-glutamate than the GDK-9, and yielded lower levels of such by-products as -ketoglutarate, L-lactate and L-alanine. Since dissolved oxygen (DO) is one of main factors affecting L-lactate formation during L-glutamate fermentation, we investigated the effect of ldhA deletion from GDK-9 under different DO conditions. Under both oxygen-deficient and high oxygen conditions, L-glutamate production by GDK-9ldhA was not higher than that of the GDK-9. However, under micro-aerobic conditions, GDK-9ldhA exhibited 11.61% higher L-glutamate and 58.50% lower L-alanine production than GDK-9. Taken together, it is demonstrated that deletion of ldhA can enhance L-glutamate production and lower the unwanted by-products concentration, especially under micro-aerobic conditions.

1. fermentation
2. L-glutamate
3. L-lactate dehydrogenase
4. gene knockout
5. Corynebacterium glutamicum