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

Abstract

A dynamic model of glucose overflow metabolism in batch and fed-batch cultivations of Escherichia coli W3110 under fully aerobic conditions is presented. Simulation based on the model describes cell growth, respiration, and acetate formation as well as acetate reconsumption during batch cultures, the transition of batch to fed-batch culture, and fed-batch cultures. E. coli excreted acetate only when specific glucose uptake exceeded a critical rate 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 dynamic situations was tested by challenging the model with glucose and acetate 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 absence of glucose. The cells showed no significant difference in maximum specific uptake rate of endogenous acetate produced by glucose overflow and exogenous 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 constant (ki) being 9 g of acetate/L. This was due to the reduced rate of glucose uptake rather than the reduced yield of biomass.