Metabolic Pathway Reformation And Regulation Analysis For Succinic Acid Production By Escherichia Coli

Escherichia coli MLB which is a pflB and ldhA double mutant ferment glucose very slowly because of redox imbalance.The NADH generated in glycolysis cannot convert into NAD+ effectively.The consumption rates of glucose is only 0.41 gL-1h-1 and the productivity of succinic acid is 0.25 gL-1h-1 during 24.73h anaerobic fermentation.The succinic acid yield of glucose is 0.62g/g.However,MLBZ which is zwf gene deletion of MLB can metabolize glucose at a high rate anaerobiclly.The consumption rates of glucose is 1.00 gL-1h-1 and the productivity of succinic acid is 0.72 gL-1h-1 during 34.75h anaerobic fermentation,1.45 times and 1.88 times higher than MLB,respectively.The results of PCR and sequencing demonstrates ptsG of both MLB and MLBZ have not spontaneous mutations.Further Studies of qRT-PCR indicate that difference exist in gene expression between MLB and MLBZ.In the end of aerobic stage,the expression of gene ace A,mdh,acnA,frdA,ppc,pck,pps,aceB and me in MLBZ are higher with different degree than that in MLB.In general,the gene transcript levels correlate with enzyme activity,that is,high transcript level means high enzyme activity.High enzyme activity in the end of aerobic stage in MLBZ can catalyze glucose convert into succinic acid rapidly in anaerobic stage.