The Study Of Blocking Byproduct Pathway Of Glycerol Metabolic On The 1,3-propanediol Fermentation In Klebsiella.Pneumoniae

K.pneumoniae is a vital industrial microorganism,which can use glycerol as the substrate to produce 1,3-propanediol(1,3-PD).1,3-PD is the product of the reductive pathway,while byproducts such as lactic acid, acetic acid and 2,3-butanediol(2,3-BD) were produced in the oxidative pathway.In this study, the lactic acid pathway was firstly blocked to study the effect of lactic acid on 1,3-PD production. Two mutant KG1-1 and KG 1-2 were constructed by knocking out the genes of ldhA(990 bp) and dld-1dhA (1746 bp) respectively, which are both encoding for the lactic dehydrogenase. By analyzing the fermentation broth of the two mutants, KG1-1 was confirmed as the D-lactic acid deficient mutant with almost no D-lactic acid produced and nearly no increase on 1,3-PD. In order to obtain the 1,3-PD high-producing mutant, KG 1-3 and KG 1-4 were constructed by knocking out the budA+B and budC respectively to block the 2,3-BD pathway. The metabolism analysis of the two mutants showed that KG 1-3 was the 2,3-BD deficient mutant. The yield of 1,3-PD and cell density decreased 60% and 43%, while the lactic acid and pyruvate increased 225% and 140%. In order to increase the 1,3-PD production, KG 1-5 was constructed by knocking out the idhA on the basis of KG 1-3 and the 1,3-PD production and cell density were recoverd by 70% and 90% compared with the parent.