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Title:Engineering Zymomonas mobilis for efficient fuel ethanol production from lignocellulosic feedstocks
Author(s):Dunn, Kori
Advisor(s):Rao, Christopher V.
Department / Program:Chemical & Biomolecular Engr
Discipline:Chemical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:M.S.
Genre:Thesis
Subject(s):Zymomonas mobilis
cellulosic ethanol
pentose sugars
xylose
sugar transport
XylE
fermentation
Abstract:The bacterium Zymomonas mobilis is of interest for the commercial production of fuel ethanol from lignocellulosic feedstocks due to its high ethanol productivity. Z. mobilis has been engineered to ferment all of the sugars present in cellulosic biomass, but the digestion of five carbon sugars by the strain is still slow and inefficient. The inefficiencies are present because Z. mobilis displays preferential sugar digestion—only after all six carbon sugars in the culture medium are depleted will five carbon sugars be consumed. This is not due to an internal regulatory mechanism, but is instead due to the fact that Z. mobilis cannot efficiently transport pentose sugars into the cell. Therefore, in this work, we investigated the effect on ethanol production of introducing a dedicated transporter for the five carbon sugar xylose in recombinant Z. mobilis. Specifically, the xylE transporter gene from Escherichia coli was expressed in a xylose-fermenting strain of Z. mobilis and glucose-xylose co-fermentation and xylose fermentation were analyzed. The engineered strain showed faster xylose consumption in the presence of glucose when the concentration of both sugars was high—in media containing 5% glucose and 5% xylose, 100% more xylose was consumed and 20% more ethanol was produced after 55 hours compared to the control strain. The engineered strain was also able to produce more ethanol in media containing a high concentration of xylose as sole carbon source, with over 100% more ethanol being produced after a 110-hour period. Additionally, the transporter also allowed for quantifiable ethanol production in media containing a very low percentage of carbon sources. These data indicate that introducing pentose-specific transporters in recombinant Z. mobilis is an effective approach toward engineering cellulosic ethanol production by the strain.
Issue Date:2013-05-28
URI:http://hdl.handle.net/2142/44783
Rights Information:Copyright 2013 Kori Dunn
Date Available in IDEALS:2013-05-28
2015-05-28
Date Deposited:2013-05


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