The Primary Study On The Alteration Of The Carbonhydrate Metabolism Of Industrial Riboflavin-producing Strain

In the riboflavin over producing B. subtilis strains, the ratio between EMP pathway and pentose phosphate pathway is constant (about 7:3). The pentose phosphate pathway is controlled by the growth rate of the cell, this pathway is direct ratio with growth rate. And ratio between the two pathways is the bottleneck of the riboflavin producing. If we want to produce more riboflavin, changing the ratio between the two pathways in order to amply the pentose phosphate pathway is needed.By genetic engineering, we constructed the pgi mutant strain B. subtilis24B. The strain is based on the strain B. subtilis24A1, which is the transketolase and CcpA mutant. B. subtilis24B cannot use the glucose as the only carbon resource for growth, this also indicates that the glucose cannot go into EMP pathway, it can only go into PP pathway. In the fermentation medium, 5% fructose is enough for the growth use for the B. subtilis24B. By using the mixture carbon resource of fructose and glucose, we have a primary study on changing the ratio between the EMP pathway and PP pathway. We also cloned the two genes zwf and gndA, in order to know the effect of the gene dosage on the PP pathway.The experiment results show that increasing the concentration of the glucose cannot amply the flux of PP pathway. And it cannot influence the riboflavin producing. So the PP pathway is controlled by unknown metabolism mechanism. Amplying the two gene zwf and gndA is helpful for the glucose absorption, but the enzyme activity should have other regulating mechanism.