Modeling of overflow metabolism in batch and fed-batch cultures of Escherichia coli

A dynamic model of glucose overflow metabolism in batch and fed-batch culti vations of Escherichia coli W3110 under fully aerobic conditions is present ed. Simulation based on the model describes cell growth, respiration, and a cetate formation as well as acetate reconsumption during batch cultures, th e transition of batch to fed-batch culture, and fed-batch cultures. E. coli excreted acetate only when specific glucose uptake exceeded a critical rat e corresponding to a maximum respiration rate. In batch cultures where the glucose uptake was unlimited, the overflow acetate made up to 9.0 +/- 1.0% carbon/carbon of the glucose consumed. The applicability of the model to dy namic situations was tested by challenging the model with glucose and aceta te pulses added during the fed-batch part of the cultures. In the presence of a glucose feed, E. coli utilized acetate 3 times faster than in the abse nce of glucose. The cells showed no significant difference in maximum speci fic uptake rate of endogenous acetate produced by glucose overflow and exog enous acetate added to the culture, the value being 0.12-0.18 g g(-1) h(-1) during the entire fed-batch culture period. Acetate inhibited the specific growth rate according to a noncompetitive model, with the inhibition const ant (k(i)) being 9 g of acetate/L. This was due to the reduced rate of gluc ose uptake rather than the reduced yield of biomass.