Mathematical modelling of lipid production by oleaginous yeasts in continuous cultures

A mathematical model was constructed to describe the influence of the carbon to nitrogen ratio (C/N-ratio) of the growth medium on lipid production by oleaginous yeasts. To test this model and to determine some relevant model parameters, the oleaginous yeast Apiotrichum curvatum ATCC 20509 was grown in continuous cultures at various C/N-ratios and dilution rates. It appeared that when nitrogen is limiting for the formation of biomass, the remaining glucose can be converted to storage carbohydrate and storage lipid. No clear dependence of carbohydrate yield on the C/N-ratio could be demonstrated, but lipid yield increased gradually with increasing C/N-ratios. The maximal dilution rate for lipid producing yeast cells appeared to be optimal at relatively low C/N-ratios. It can be concluded that the experimental results fitted well with the mathematical model. By using this model, lipid yield and lipid production rate can be calculated at any C/N-ratio of the growth medium and optimum operation conditions can be predicted for the production of microbial lipids.