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
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
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.