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.