New Yeasts Could Help Fast-Track Biofuel
By Ann Perry
July 28, 2009
A new yeast that makes ethanol from
both five-carbon and six-carbon sugars without needing oxygen has been
developed by an Agricultural
Research Service (ARS) scientist.
This could be an important breakthrough in industrial ethanol production,
because it’s difficult to control oxygen levels as yeasts ferment sugars
into ethanol. The new yeast strain would help alleviate this problem.
Producers already make grain ethanol by using yeast to ferment six-carbon
plant sugars like glucose. But cost-effective production of cellulosic
ethanol will require using both six-carbon and five-carbon sugars in the
ARS molecular biologist
Hughes developed the first yeast strain that doesn’t require oxygen
to grow on xylose, a five-carbon plant sugar. Hughes works at the
National Center for Agricultural Utilization Research in Peoria, Ill.
The new yeast doesn’t directly convert large quantities of xylose into
ethanol. Instead, xylose provides energy the yeast needs to grow and
reproduce without oxygen. This means that the glucose that might have
been used by the yeast to grow and reproduce is now available for fermentation,
and the rate of ethanol conversion increases.
To begin this research, Hughes developed a yeast strain containing a gene
that makes an enzyme for converting xylose into ethanol. He added
another gene to the strain so that the yeast could metabolize the xylose more
Then Hughes created 6,113 different yeast strains that contained both genes,
and screened all of the strains for traits for enhanced ethanol
production. He found seven strains that were able to convert both glucose
and xylose into ethanol without oxygen.
But the seven yeast strains had relatively low rates of xylose fermentation,
so Hughes and his group screened the strains for genes that could step up
xylose’s contribution to ethanol conversion in other ways. They
found five genes associated with the enzyme that converts xylose into ethanol,
and confirmed that these five genes play a critical role in yeast cell
This research has been published in the August 2009 Journal
of the Association of Laboratory Automation theme issue on biofuels
ARS is the principal intramural scientific research agency of the
U.S. Department of