Location: Bioenergy Research Unit
Title: Evaluation of a kinetic model for computer simulation of growth and fermentation by Scheffersomyces (Pichia) stipitis fed D-xylose Authors
Submitted to: Biotechnology and Bioengineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 5, 2014
Publication Date: March 18, 2014
Citation: Slininger, P.J., Dien, B.S., Lomont, J.M., Bothast, R.J., Ladisch, M.R., Okos, M.R. 2014. Evaluation of a kinetic model for computer simulation of growth and fermentation by Scheffersomyces (Pichia) stipitis fed D-xylose. Biotechnology and Bioengineering. DOI: 10.1002/bit.25215. Interpretive Summary: Lignocellulosic biomass is an abundant, non-food, non-feed renewable feedstock that is potentially useful for the production of low cost fuel-grade ethanol. It has been estimated that enough lignocelluloses can be collected from wastes and harvested as bioenergy crops to supply over 1 billion tons per year of biomass. However, a major technical hurdle to this realizing this vision is the fermentation of xylose. Unlike these grains and sugar crops, lignocellulose contains up to 40% xylose. Xylose is a 5 carbon sugar that is not fermented by the traditional yeasts for foods and beverages. The yeast Scheffersomyces stipits is unique because it natively ferments xylose and can produce economically harvestable levels of ethanol. We have constructed a mathematical model based on observed performance of this yeast under defined growth and fermentation conditions. We have now tested the model using batch, cell recycling, batch with in situ ethanol removal and fed-batch processes and proven that it accurately predicts yeast growth and ethanol production as functions of the variables of the progressing fermentation process, including sugar concentrations, ethanol, and oxygen. The model is an important tool for simulating and optimizing various culture conditions and evaluating various bioreactor designs for ethanol production. The new simulation model will be useful to the biofuels industry and to other scientists studying metabolism and physiology and designing improved processes for the production of ethanol biofuel. As a result, it furthers our progress toward national priorities of achieving energy independence, strengthening our rural economy, and preserving our environment.
Technical Abstract: Scheffersomyces (formly Pichia) stipitis is a potential biocatalyst for converting lignocelluloses to ethanol because the yeast natively ferments xylose. An unstructured kinetic model based upon a system of linear differential equations has been formulated that describes growth and ethanol production as functions of ethanol, oxygen, and xylose concentrations for both growth and fermentation stages. The model was validated for various growth conditions including batch, cell recycle, batch with in situ ethanol removal and fed-batch. Integrating basic kinetic and physiological yeast properties, the model is an important predictive tool for simulating and optimizing various culture conditions and evaluating various bioreactor designs for ethanol production.