Semi-Quantitative Modeling for the Effect of Oxygen Level on the Metabolism in Escherichia coli

Mathematical models for the main metabolic pathways such as glycolysis, pentose phosphate pathway, TCA cycle, fermentation pathway etc. were considered for the enzyme level regulation in E.coli. It is quite important to develop a model which can simulate the effect of oxygen level on the metabolism in practice. For this, the effect of oxygen level on the expressions of the global regulators such as arcA/B and fnr was modeled based on the experimental data. Then the effects of these gene expressions on the metabolic pathway gene expressions were incorporated in the model, where the effects of oxygen levels on PDHc and Pfl fluxes as well as the respiratory pathway flux were expressed based on the experimental data. Thus, the model could express the increase in the redox ratio, NADH/NAD as the oxygen level decreases, and in turn the activation of the fermentation pathways. The semi-quantitative model developed in the present research enables us to simulate the effect of changing the oxygen level on the cell growth and the production of the variety of metabolites such as lactate, ethanol etc.