Yeast plus agricultural wastes equals ethanol

WEST LAFAYETTE, Indiana, June 29, 2004 (ENS): A strain of yeast developed at Purdue University makes ethanol from agricultural residues more effectively than other yeast strains.
Purdue's genetically altered yeast allows about 40 percent more ethanol to be made from sugars derived from agricultural residues, such as corn stalks and wheat straw, compared with "wild-type" yeasts that occur in nature.

The agricultural residues are made up of cellulose and hemicellulose, known as cellulosic materials. These are materials such as wheat straw that would otherwise be discarded or used as animal feed.

Unlike traditional ethanol feedstocks, such as corn kernels, the cellulosic materials contain two major sugars, glucose and xylose.

Neither sugar can be fermented into ethanol by the natural yeast used by industry to produce ethanol, explained Nancy Ho, a senior research scientist and leader of the molecular genetics group in Purdue's Laboratory of Renewable Resources Engineering.

"It would cost too much money to separate the two sugars before proceeding with fermentation to ethanol, so being able to ferment both sugars together to ethanol is critical," she said. "To be more cost competitive with gasoline, the two sugars have to be converted together to ethanol."

A team led by Ho developed the more efficient yeast during the 1980s and 1990s. "Until we developed our yeast, no suitable microorganism could convert these two sugars together," she said.

Conventional yeast can ferment glucose to ethanol, but it cannot ferment xylose, which makes up about 30 percent of the sugar from agricultural residues. The inability to ferment xylose would represent a major loss of ethanol yield, Ho explained.

The Purdue researchers altered the genetic structure of the yeast so that it now contains three additional genes that make it possible to simultaneously convert glucose and xylose to ethanol.

The ability to ferment xylose increases the yield of ethanol from straw by about 40 percent.

The first license for the yeast has been issued to the biotechnology company Iogen Corp., which specializes in producing ethanol from cellulosic material.

Iogen is using the Purdue yeast to produce ethanol from the sugars the company derives from wheat straw.

The ethanol made in Iogen's plant is blended into gasoline at the Petro-Canada refinery in Montreal. Cars can use the ethanol-gasoline blend without any engine modifications.

http://www.ens-newswire.com/ens/jun2004/2004-06-29-09.asp#anchor9

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