Knockout of the HprK Gene in Bacillus subtilis CcpA Mutant and Its Influence on Riboflavin Fermentation

In Bacillus subtilis, increasing the carbon catabolite content in vivo would lead to carbon catabolite repression (CCR) and restrain the absorption of glucose. By deleting CcpA, the CCR effect could be alleviated, while the absorption of glucose remains restrained. The phosphoenol-pyruvate (PEP)-sugar phosphotransferase system (PTS) is the main glucose transportation system in B. subtilis. HPr protein together with HprK/P participates in the glucose transportation. The HPr protein is phosphorylated at His-15 resulting in the formation of HPr-His-15-P, and the phosphate group is transferred from HPr to E II. The HprK/P phosphorylates HPr at Ser-46 form HPr-Ser-46-P. HPr-Ser-46-P cannot participate in the transportation of glucose. The knockout of ccpA gene increases the amount of fructose-1, 6-bisphosphate (FBP) in vivo and FBP could activate HPr kinase. So when CcpA is deleted, most part of HPr will be phosphorylated at Ser-46. Therefore, absorption of glucose is blocked. In this study, by disruption of the hprK gene, the obtained B. subtilis ZHc/pMX45 reaches the peak riboflavin production of 4.374 mg/mL at the optimum glucose concentration of 10%, 19.2% higher than that of B. subtilis 24A1/pMX45 at the optimum glucose concentration of 8%.