大肠杆菌苹果酸有氧发酵溢出机制的解析及其应用OACSTPCD

The utilization of renewable biomass to produce L-malic acid,an important C4 dicarboxylic acid,has attracted significant interests in past years.Herein,we investigated the aerobic synthesis of L-malic acid regarding the influence from several key factors including nitrogen limited conditions,temperature,and pH.As a result,nitrogen limited conditions played a pivotal role in the accumulation of L-malic acid.Additionally,the optimal temperature and pH for the synthesis were determined to be 35℃ and 6.8,respectively.Based on the analysis of cofactor concentrations and transcription levels for genes associated with the respiratory chain,the excessive accumulation of L-malic acid might be attributed to the declining efficiency of the electron respiratory chain.In other words,inadequate oxidation of NADH and insufficient availability of NAD+impeded the catalytic conversion of L-malic acid to oxaloacetic acid,leading to the excretion of L-malic acid into the extracellular environment.As the removal of gene ndh in NADH dehydrogenase Ⅱ could decrease the electron respiratory chain efficiency,the recombinant E.coli AFP111(Δndh)exhibited the ability to metabolize a significant quantity of succinic acid,affording L-malic acid as the primary product with a yield of 0.65 g/g under nitrogen sufficient conditions.Our research demonstrated that the respiratory chain modification could enhance the overflow metabolism of intermediate metabolites,offering valuable theoretical support and guidance in this field.