Geneticist Working on Mutant Yeast for Ethanol Production

A yeast geneticist on the campus of Indiana University-Purdue University Indianapolis is close to developing mutant yeast for ethanol production that would reduce or eliminate the need to use corn to make the alternative fuel, according to a recent press release.

The production of biofuels from basic plant material, rather than corn and other crops, would address concerns that making corn-based ethanol is pushing up food costs, said Mark Goebl, a professor of Biochemistry and Molecular Biology in the IU School of Medicine.

Goebl's work is part of the Richard G. Lugar Center for Renewable Energy, which was established to address the societal needs for clean, affordable and renewable energy sources, improve the nation's energy security, and reduce global warming.

Goebl said the crux of the problem of using basic plant material to make ethanol involves how yeast decide what they will eat. When corn is used to make ethanol, yeast couldn't be happier. Corn kernels are ground to produce starch and the starch is broken down into glucose. Yeast is then used to ferment the glucose into ethanol.

"Although yeast can derive energy from a lot of different carbon sources, such as fatty acids and different kinds of sugars, yeast really, really like glucose, the sugar found in honey," Goebl said. "That's what they will use if it's there, even if it's there only in trace amounts."

And that's where the sticking point occurs. During the fermentation process, there is always a trickle of glucose coming into the system.

Unlike corn kernels, one-third of basic plant material consists of compounds that produce pine resins for which there are useful purposes. One- third is cellulose, which can be converted to glucose and used to make ethanol. But one-third is another kind of sugar, xylose, which yeast turn away from. Goebl has developed strains of yeast that will utilize the xylose, even if glucose is around.

"Yeast essentially care about glucose because they are genetically programmed that way, not because there is any physiological reason they have to care about glucose," he said. "We can genetically change that program. We are using genetics to modify yeast strains so that they will use other sugars just as well as glucose."

Producing mutant yeast strains that will eat xylose just as well as glucose means nearly doubling the amount of ethanol you get from the same volume of basic plant material.

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