Date of Award

12-2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Microbiology

Advisor

Henson, J. Michael

Committee Member

Harcum , Sarah W

Committee Member

Kurtz, Jr , Harry D

Abstract

The importance of biofuel ethanol is growing as the demand for clean, renewable fuels produced from non-food sources increases. The United States relies mainly on corn and the yeast Saccharomyces cerevisiae for the production of ethanol. A shift to cellulosic feedstocks, as the main source of biomass for ethanol production, would alleviate the pressure on farmers to produce corn for both the food industry and the ethanol industry. Example cellulosic feedstocks include switchgrass, sorghum, and canary grass. The cellulosic feedstocks are typically grown on land that cannot support economic food production, and thus lay unused.
For cellulosic feedstocks to be used for ethanol production, the cellulose must be converted to sugars via a process known as hydrolysis. Hydrolyzed switchgrass is an ideal substrate for ethanol production in South Carolina and many southern states because of the humid subtropical climate. Switchgrass hydrolysate contains both five- and six-carbon sugars, where the six-carbon sugars (mainly glucose) are easily used by yeast to produce ethanol. The five-carbon sugars (mainly xylose) are not directly usable by most yeast to produce ethanol. However, yeast can metabolize xylulose, which can be obtained from xylose by an enzymatic conversion using the enzyme xylose isomerase. In order to economically produce ethanol from cellulosic feedstocks, such as hydrolyzed switchgrass, both the five- and six-carbon sugars need to be metabolized. The long term goal of this research is to produce ethanol cost effectively from hydrolyzed switchgrass using the yeast species Saccharomyces bayanus.
The specific hypothesis of this study is that S. bayanus, in conjunction with the enzyme xylose isomerase, will metabolize both glucose and the isomer of xylose, xylulose, to produce ethanol. This hypothesis is based on the following observations: 1) S. bayanus can ferment glucose into ethanol; 2) S. bayanus can metabolize xylulose; 3) xylulose can be enzymatically obtained from xylose; 4) S. bayanus can grow in a medium with xylose as the sole carbon source, if xylose isomerase is present. Based on these observations, the experimental focus of this research is to develop and assess methods that allow S. bayanus to convert hydrolyzed switchgrass into ethanol. The experiments are designed to assess the capability and economics of ethanol production using S. bayanus and xylose isomerase.

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Microbiology Commons

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