July 5, 2004

New US Yeast Strain To Improve Ethanol Production

Biotechnology firm Iogen Corp. has obtained the license for a new strain of genetically modified yeast, developed at Purdue University, that more effectively makes ethanol from agricultural residues that would otherwise be discarded or used as animal feed.
 
The genetically modified yeast allows about 40% 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, said Nancy Ho, a senior research scientist and leader of the molecular genetics group in Purdue's Laboratory of Renewable Resources Engineering, or LORRE.
 
The agricultural residues are primarily made up of cellulosic materials, Ho said. Unlike traditional ethanol feedstocks, the cellulosic materials contain two major sugars, glucose and xylose, which cannot both be fermented into ethanol by natural Saccharomyces yeast, the microorganism used by industry to produce ethanol.
 
"In traditional yeast, it cannot ferment that particular sugar called xylose," Ho said. It can ferment glucose to ethanol.
 
Xylose makes up about 30% of the sugar from agricultural residues, and the inability to ferment xylose would represent a major loss of ethanol yield, she said.
 
Ho and 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, she said. The ability to ferment xylose increases the yield of ethanol from straw by about 40%. Being able to simultaneously ferment glucose and xylose is important because both sugars are found together in agricultural residues, Ho said.
 
The cost to separate the two sugars before proceeding with fermentation to ethanol is expensive, so being able to ferment both sugars together to ethanol is beneficial, making ethanol "as cheap as possible," she said. Before the new yeast, no suitable microorganism could convert the two sugars together.
 
Ethanol currently is produced when yeast ferments glucose and related hexose, or six-carbon sugars in food crops such as cane sugar, corn and other starch-rich grains. However, because these crops are expensive and in relatively limited supply, they can't yield sufficient amounts of ethanol for transportation needs, Ho said.
 
Cellulosic materials will address the problem since the cost is only about half as much as corn per ton, but are more difficult than corn to convert to ethanol. Part of the difficulty is the fermentation to ethanol of the xylose, which is a five-carbon sugar. Yeast or other microorganisms do not naturally ferment this sugar.
 
The use of cellulosic materials to produce ethanol could also open up new market opportunities, create jobs and provide more energy independence, Ho said.
 
The yeast has to be approved by regulatory agencies, which will take time, but technology is ready, Ho said. At most, it will take four years before plants start production using the genetically modified yeast, she said.
 
The U.S. Department of Agriculture, the Department of Energy, the Consortium for Plant Biotechnology Research Inc., the U.S. Environmental Protection Agency and industry sources have funded Ho's research. The scientists are looking for additional funding in order to perfect the strain.
 
Ho said the scientists would like to see use the yeast start in the U.S.
 
So far, the genetically modified strain has been tested only in the lab, said Michael Ladisch, distinguished professor of agricultural and biological engineering and director of LORRE.
 
"The next step is to test in the U.S. with other types of cellulosic materials," Ladisch said.
 
Iogen Corp., which specializes in producing ethanol from cellulosic material, has obtained a non-exclusive license from the Purdue Research Foundation for the yeast and related patents. Its Ottawa, Canada, demonstration facility is the first plant in the world to produce ethanol from cellulosic materials. Iogen is using the Purdue-developed yeast to produce ethanol from the sugars the company derives from wheat straw.
 
Iogen is very active to make production better with the newest technology, Ho said.
 
"Their license is nonexclusive unlike other companies," Ho said. "They won't give exclusive rights." This will make production fair for everyone, she said.
 
The strain can be used for ethanol production, but improvements can still be made to perfect the yeast strain and co-products may be discovered, Ho said.
 
Ethanol is the major product the scientists wanted, but there could be others, Ho said.
 
Currently, the ethanol yield is close to 90% of the conversion. That time can be shortened if scientists improve the strain and if co-produced, the strain will be much more profitable, Ho said. Theoretically, 100 pounds of material will produce 4 billion to 4.5 billion gallons of ethanol at a 100% conversion rate.
 
Ethanol can be used as fuel by itself or blended with gasoline.
 
Ladisch said ethanol is a cleaner fuel than gasoline and provides benefits to the environment.
 
"It's an indirect way of using solar energy," he said.
 
When ethanol is burned, the sun converts the carbon dioxide generated back into plant matter, which can be converted back into ethanol, Ladisch said.