A University of Illinois metabolic¹（变化的，新陈代谢的） engineer has taken the first step toward the more efficient and economical production of biofuels by developing a strain of yeast²（酵母，泡沫） with increased alcohol tolerance³. Biofuels are produced through microbial fermentation（发酵） of biomass crops, which yield the alcohol-based fuels ethanol（乙醇，酒精） and iso-butanol（丁醇） if yeast is used as the microbe to convert sugars from biomass into biofuels.

"However, at a certain concentration, the biofuels that are being created become toxic⁴ to the yeast used in making them. Our goal was to find a gene⁵ or genes⁶ that reduce this toxic effect," said Yong-Su Jin, an assistant professor of microbial genomics in the U of I Department of Food Science and Human Nutrition and a faculty⁷ member in the U of I's Institute for Genomic Biology.

Jin worked with Saccharomyces cerevisiae（酿酒酵母） , the microbe most often used in making ethanol, to identify four genes (MSN2, DOG1, HAL1, and INO1) that improve tolerance to ethanol and iso-butanol when they are overexpressed.

"We expect these genes will serve as key components⁸ of a genetic⁹ toolbox for breeding yeast with high ethanol tolerance for efficient ethanol fermentation," he said.

To assess the overexpressed genes' contribution to the components that have limited biofuel production, the scientists tested them in the presence of high concentrations of glucose¹⁰（葡萄糖） (10%), ethanol (5%), and iso-butanol (1%) and compared their performance to a control strain of S. cerevisiae.

Overexpression of any of the four genes remarkably¹¹ increased ethanol tolerance, but the strain in which INO1 was overexpressed elicited¹²（抽出，引起） the highest ethanol yield and productivity—with increases of more than 70 percent for ethanol volume and more than 340 percent for ethanol tolerance when compared to the control strain.

According to Jin, the functions of the identified genes are very diverse and unrelated, which suggests that tolerance to high concentrations of iso-butanol and ethanol might involve the complex interactions of many genetic elements in yeast.

"For example, some genes increase cellular¹³ viability¹⁴ at the expense of fermentation. Others are more balanced between these two functions," he said.

"Identification of these genes should enable us to produce transportation fuels from biomass more economically and efficiently¹⁵. It's a first step in understanding the cellular reaction that currently limits the production process," he said.

Further study of these genes should increase alcohol tolerance even further, and that will translate into cost savings¹⁶ and greater efficiency during biofuel production, he added.