Mathematical model for aerobic culture of a recombinant yeast

Abstract

A mathematical model was formulated to simulate cell growth, plasmid loss and recombinant protein production during the aerobic culture of a recombinant yeast S. cerevisiae. Model development was based on three simpli®ed metabolic events in the yeast: glucose fermentation, glucose oxidation and ethanol oxidation. Cell growth was expressed as a composite of these metabolic events. Their contributions to the total speci®c growth rate depended on the activities of the pacemaker enzyme pools of the individual pathways. The pacemaker enzyme pools were regulated by the speci®c glucose uptake rate. The effect of substrate concentrations on the speci®c growth rate was described by a modi®ed Monod equation. It was assumed that recombinant protein formation is only associated with oxidative pathways. Plasmid loss kinetics was formulated based on segregational instability during cell division by assuming constant probability of plasmid loss. Experiments on batch fermentation of recombinant S. cerevisiae C468/pGAC9 (ATCC 20690), which expresses Aspergillus awamori glucoamylase gene and secretes glucoamylase into the extracellular medium, were carried out in an airlift bioreactor in order to evaluate the proposed model. The model successfully predicted the dynamics of cell growth, glucose consumption, ethanol metabolism, glucoamylase production and plasmid instability. Excellent agreement between model simulations and our experimental data was achieved. Using published experimental data, model agreement was also found for other recombinant yeast strains. In general, the proposed model appears to be useful for the design, scale-up, control and optimization of recombinant yeast bioprocesses.

Topology optimized microbioreactors

“…In this model a certain fraction of the yeast cells was assumed to possess a plasmid which encodes for a recombinant protein, the product we aimed to obtain from the cultivation (Zhang et al, 1997). Glucose was fed to the reactor, and was assumed to be the preferred substrate.…”

“…A new model (schematically presented in Fig. 1, equations provided in Appendix 1), based both on the work of Brányik et al (2004) and Zhang et al (1997), was required in order to perform the topology optimization. The purpose of the new model is to simulate a cultivation in a microbioreactor where brewing yeast, both immobilized onto a support (carrier) and suspended in the cultivation medium, grows, and produces an extracellular soluble recombinant protein P, which is encoded in a plasmid.…”

“…Glucose was fed to the reactor, and was assumed to be the preferred substrate. The yeast metabolism was simplified to a three-pathway model suggested by Zhang et al (1997). A new model (schematically presented in Fig.…”

Evaluation of wavelength selection methods for 2D fluorescence spectra applied to bioprocesses characterization

“…When S. cerevisiae is grown in glucose, even under aerobiosis, biomass and ethanol are produced and a diauxic pattern can be observed (Zhang et al, 1997). The system can be modeled by the following three differential equations:…”

A Model Based Simulation of Brewing Yeast Propagation

“…Temperature dependency and maintenance energy are not considered. Also, a lag-time function to describe the adaptation of the microorganisms to the surrounding growth medium, including the time for formation of enzymes, is merely included in single approaches using different equations 12,23,33 . The maintenance energy of the microorganisms is only considered in single approaches, e.g.…”