大肠杆菌及其耐乙酸突变菌的连续培养和代谢流比较

在氮源限制基本培养基中连续培养大肠杆菌DH5α及其乙酸耐受突变株DA19。与DH5α相比，突变株DA19降低了葡萄糖的消耗，减少了乙酸和丙酮酸的生成，提高了菌体关于葡萄糖的得率。利用物料平衡和代谢反应的化学计量关系，分析了二者在比生长速率0.13 h^-1下的稳态代谢流分布。与DH5α相比，DA19的三羧酸循环流量高，酵解途径的流量低，从而减少了乙酸等副产物的分泌，反映了能量代谢效率的明显提高。比较了二者异柠檬酸裂解酶、6-磷酸葡萄糖脱氢酶、磷酸果糖激酶、异柠檬酸脱氢酶和乙酸激酶的活性，酶活变化与代谢流结果基本一致。

Comparison of metabolic fluxes in Escherichia coli and its acetate-tolerant mutant in continuous culture

Escherichia coli DH5α and its acetate-tolerant mutant DA19 were continuously cultured in nitrogen-limited defined media.Compared with DH5α, DA19 showed improved growth yield due to decreased specific glucose consumption rate and formation of less acetic acid and pyruvate at a similar dilution rate.Based on mass balance and metabolic reaction stoichiometry, the metabolic flux distribution in DH5α and DA19 at a dilution rate of 0.13 h^-1 was calculated.Compared with DH5α, DA19 had a higher flux of tricarboxylic acid cycle and a lower flux of Embden-Meyerhof-Parnas pathway so it decreased the secretion rate of by-products, such as acetate and pyruvate.This indicated that DA19 had higher efficiency in energy metabolism. The activities of isocitrate lyase, 6-phosphoglucose dehydrogenase, phosphofructokinase, isocitrate dehydrogenase and acetokinase were measured, and the difference of activities between the two strains were consistent with the difference of metabolic fluxes.