Development of a structured model for biopolymer synthesis in the fungus Aureobasidium pullulans

Previous modelling of the pullulan fermentation is discussed and found to lack any mechanistic basis. It is concluded that predictive ability can only be conferred by a structured model with at least two compartments, based upon the best available knowledge of the physiology of the microorganism. Such a model is constructed and compared with experimental data.List of Symbols A (gdm^–3)(g/l) Ammonium ion concentration - B (gdm^–3)(g/l) Concentration of balanced growth compartment of biomass - G (gdm^–3)(g/l) Glucose concentration - k_A (gdm^–3)(g/l) Saturation constant for ammonium - k_G (gdm^–3)(g/l) Saturation constant for glucose - k_S (gdm^–3)(g/l) Saturation constant for sucrose - P (gdm^–3)(g/l) Pullulan concentration - Q Quality of biomass=U/(U+B) - r_G (gdm^–1h^–1)(g/l/h) Rate of removal of glucose from broth - r_GB (gdm^–3h^–1)(g/l/h) Rate of incorporation of glucose into balanced compartment - r_GB (gdm^–3h^–1)(g/l/h) Rate of utilisation of glucose for energy production and cell maintenance - r_GP (gdm^–3h^–1)(g/l/h) Rate of conversion of glucose to pullulan - r_GU (gdm^–3h^–1)(g/l/h) Rate of incorporation of glucose into unbalanced compartment - r_s (gdm^–3h^–1)(g/l/h) Rate of conversion of sucrose to glucose - S (gdm^–3)(g/l) Concentration of sucrose - U (gdm^–3)(g/l) Concentration of unbalanced growth compartment of biomass - X (gdm^–3)(g/l) Biomass concentration - Y_G/A Grams of glucose consumed per gram of ammonium consumed - Y_G/B Grams of glucose consumed per gram of balanced biomass produced - Y_G/U Grams of glucose consumed per gram of unbalanced biomass produced - Y_G/P Grams of glucose consumed per gram of pullulan produced - Rate constant for conversion of sucrose to glucose - Rate constant for uptake of glucose by the cells - Model parameter governing inhibition of sucrose conversion and glucose utilisation - Model parameter denoting fraction of glucose uptake devoted to cell maintenance and energy production - Model parameter governing apportionment of glucose between pseudo-growth and pullulan productionThis work was funded by the National Engineering Laboratory (NEL) through the Bioreactor Design Club. The authors would like to express their gratitude to the NEL for this generous support.