Inverse flux analysis for reduction of acetate excretion in Escherichia coli

The determination of intracellular fluxes from the measurement of extracellular rates, a technique known as flux analysis, has been used successfully on several systems important to biotechnology. However, calculation of intracellular fluxes does not directly suggest ways to improve the performance of the cell. Here, we introduce a variation of this analysis, termed inverse flux analysis, which allows the prediction of the flux distribution as a function of manipulable internal fluxes. This approach is applied to analyze the acetate excretion problem commonly observed in aerobic Escherichia coli cultures. The effect of manipulating each flux is quantified by a flux distribution sensitivity coefficient, which is dependent on the stoichiometry. For the acetate excretion problem, our results suggest that the anaplerotic pathways, including the reactions catalyzed by phosphoenolpyruvate carboxylase and the glyoxylate bypass are the best choices for manipulating acetate excretion in E. coli. Increasing the anaplerotic flux will decrease acetate production while increasing the growth yield.