Date of Award

12-31-2018

Document Type

Open Access Thesis

Degree Name

Master of Science (MS)

First Advisor

Linda Huang

Second Advisor

Alexey Veraksa

Third Advisor

Joe Shaw

Abstract

As the world population continues to grow, the demand for energy will continue to rise. Biofuels have become an attractive alternative to replace fossil fuels as a clean and renewable source of energy. The six- and five-carbon sugars contained in lignocellulosic plant biomass is the largest carbohydrate source in the world, and a key feedstock for sustainable biofuel production. The conversion of lignocellulose to lipids is done by using oleaginous yeast as a biocatalyst. Recently, Arxula adeninivorans has become a yeast of interest because of its unique properties. These include its unusual metabolic flexibility which allows it to utilize a wide range of carbon and nitrogen sources. Arxula adeninivorans is xerotolerant, osmotolerant, thermotolerant, and able to accumulate lipid to over 20% of its dry weight. In particular, Arxula adeninivorans has the ability to grow at higher temperatures than most other types of oleaginous yeast. A major cost in an aerobic industrial fermentation is heat removal from the fermenter. At higher temperatures, heat transfer from the fermenter to the external environment is efficiently performed via evaporative heat loss in cooling towers. In comparison, lower temperature fermentation requires an electricity demanding refrigeration cycle to transfer heat using industrial chillers. By performing experiments with Arxula adeninivorans, I sought to evaluate whether higher temperature fermentation is more cost effective. The results suggest that biomass growth is faster at 40°C, but lipid production is better at 30°C. Even with the slight reduction in lipid production at 40°C, lignocellulosic conversion still may be cheaper at 40°C because of the many advantages of higher temperature fermentation, including lower cost heat removal, higher activity of cellulase enzymes required to break down lignocellulose into sugars, and the potential reduction in contamination risk at 40°C as well. In order to improve lipid production at 40°C with Arxula adeninivorans, more strain engineering may be necessary to increase lipid productivity and reduce the tendency to form hyphal cell bodies at elevated temperature.

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