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The effects of the expression levels of cellobiose transporter and β-Glucosidase on ethanol fermentation

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Title: The effects of the expression levels of cellobiose transporter and β-Glucosidase on ethanol fermentation
Author(s): Lee, Jong Hyun
Advisor(s): Jin, Yongsu
Department / Program: Food Science & Human Nutrition
Discipline: Food Science & Human Nutrition
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: M.S.
Genre: Thesis
Subject(s): Bioethanol Cellobiose Fermentation Cellobiose transporter, Cellobiose glucosidase Femenation Efficiency
Abstract: Recently, cofermentation of cellobiose and xylose in yeasts has been reported. It is considered as one of the most innovative strategies to enhance bioethanol production from lignocellulosic fermentation. Through cofermentation with cellobiose and xylose, it is achieved to utilize most abundant two sugar substrates in lignocellulosic materials at the same time and to enhance xylose utilization by yeast through boosting cellobiose catabolism in yeast. However, cellobiose utilization by yeast to produce bioethanol has not been fully understood yet. Due to cellobiose fermentation in yeast requires the introduction of two essential enzymes such as cellobiose transporter and β-glucosidase, the ratios between those two enzymes can be a significant factor on cellobiose fermentation. In order to assess the effects of expression level of cellobiose transporter (CDT) and β-glucosidase (β-GL), in this study the copy number variation of plasmids is used to assess contributions by CDT and β-GL on cellobiose fermentation. Four different transformants contain different combinations of copy numbers in CDT and β-GL; MTMβ, MTSβ, STMβ and STSβ. The patterns of cellobiose fermentation by the transformants were evaluated. The engineered strain, MTMβ showed the best fermentation phenotypes relevant to cellobiose fermentation. The productivity of the engineered strain showed 0.588 g/h∙L, and final yield of ethanol is 0.413 g/g. Additionally, this study suggests that higher expressed CDT has more critical influence on cellobiose fermentation. When I compared MTSβ and MTMβ, I observed detrimental contribution of insufficient β-GL on cell growth and ethanol fermentation. MTSβ strain showed 1.8 fold of cellodextrin accumulation and takes more 46 hours to finish cellobiose fermentation, compared to STSβ. However, when I compared STMβ and STSβ, I observed beneficial contribution on cell growth and ethanol fermentation. MTMβ showed 0.78 fold of cellodextrin accumulation and takes less12 hours to finish cellobiose fermentation, compared to STMβ. Taken these two observations together, it is suggested that in the case of ensuring sufficient quantities of β-GL, overexpression of CDT provide beneficial effects on cellobiose fermentation.
Issue Date: 2012-06-27
URI: http://hdl.handle.net/2142/32014
Rights Information: Copyright 2012 Jong Hyun Lee
Date Available in IDEALS: 2012-06-27
Date Deposited: 2012-05
 

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