Effect of cra gene knockout together with other genes knockouts on the improvement of substrate consumption rate in Escherichia coli under microaerobic condition

Abstract The catabolite repressor/activator protein Cra (FruR) is known to repress the glycolysis pathway genes and activate the gluconeogenic pathway genes. Disruption of cra gene may, therefore, activate glycolysis and thus improve the glucose consumption rate, which may in turn lead to the increase of the specific metabolite production rate. However, it was found in our previous investigation that the substrate consumption rate could not be improved for the aerobic cultivation of cra mutant due to activation of Entner–Doudoroff (ED) pathway, and the repression of the TCA cycle caused by the down-regulation of icd A and ace BAK genes. To overcome this problem, we investigated the effects of edd and arc A genes knockout on the glucose consumption rate. The cra.edd mutant showed the higher glucose uptake rate as compared with the wild type under microaerobic condition. Since arc A gene knockout mutant repressed pfl operon under microaerobic condition, the glucose consumption rate was not improved for cra.edd.arc A mutant. In order to show that the increase in the glucose consumption rate can lead to the increase of the metabolite production rate, we considered the lactate production by pfl A mutant. It was shown that the substrate consumption rate could be significantly improved for cra.pfl A mutant as compared with pfl A mutant, and thus the lactate production rate could be improved by this double mutant if fructose was used as a carbon source.