Glucose consumption rate critically depends on redox state in Corynebacterium glutamicum under oxygen deprivation

Rapid sugar consumption is important for the microbial production of chemicals and fuels. Here, we show that overexpression of the NADH dehydrogenase gene (ndh) increased glucose consumption rate in Corynebacterium glutamicum under oxygen-deprived conditions through investigating the relationship between the glucose consumption rate and intracellular NADH/NAD+ ratio in various mutant strains. The NADH/NAD+ ratio was strongly repressed under oxygen deprivation when glucose consumption was accelerated by the addition of pyruvate or sodium hydrogen carbonate. Overexpression of the ndh gene in the wild-type strain under oxygen deprivation decreased the NADH/NAD+ ratio from 0.32 to 0.13, whereas the glucose consumption rate increased by 27 %. Similarly, in phosphoenolpyruvate carboxylase gene (ppc)- or malate dehydrogenase gene (mdh)-deficient strains, overexpression of the ndh gene decreased the NADH/NAD+ ratio from 1.66 to 0.37 and 2.20 to 0.57, respectively, whereas the glucose consumption rate increased by 57 and 330 %, respectively. However, in a lactate dehydrogenase gene (L-ldhA)-deficient strain, although the NADH/NAD+ ratio decreased from 5.62 to 1.13, the glucose consumption rate was not markedly altered. In a tailored d-lactate-producing strain, which lacked ppc and L-ldhA genes, but expressed D-ldhA from Lactobacillus delbrueckii, overexpression of the ndh gene decreased the NADH/NAD+ ratio from 1.77 to 0.56, and increased the glucose consumption rate by 50 %. Overall, the glucose consumption rate was found to be inversely proportional to the NADH/NAD+ ratio in C. glutamicum cultured under oxygen deprivation. These findings could provide an option to increase the productivity of chemicals and fuels under oxygen deprivation.