677a Dynamic Flux Balance Models for Simulation and Optimization of Saccharomyces Cerevisiae Fed-Batch Cultures

Jared L. Hjersted and Michael A. Henson. Department of Chemical Engineering, University of Massachusetts Amherst, 686 North Pleasant Street, Amherst, MA 01003

We have previously developed dynamic flux balance models for prediction of cellular growth and metabolic product formation rates in Saccharomyces cerevisiae batch and fed-batch cell cultures. These models couple steady-state stoichiometric balances on intracellular metabolites with dynamic extracellular balances on biomass, substrates, and metabolic byproducts through time-varying substrate uptake rates. In this contribution, we present the results of Saccharomyces cerevisiae fermentation experiments designed to evaluate the dynamic flux balance model predictions. We utilized a compartmentalized, genome-scale metabolic network to describe intracellular metabolism and simple Michaelis-Menten kinetics for the glucose and oxygen uptake rates. Kinetic parameters for the substrate uptake and the intracellular stoichiometric coefficients representing growth and non-growth associated energy requirements were estimated by nonlinear least squares optimization. A series of batch and fed-batch experiments demonstrated that the dynamic flux balance model was able to produce accurate substrate, biomass, and extracellular product concentration profile predictions over a wide range of fermentation conditions. The model was incorporated with a bi-level dynamic optimization scheme to compute fed-batch operating policies for optimal ethanol production in batch and fed-batch cultures. Experimental implementation of the optimal policies showed good agreement with the in silico predictions.