Engineered yeast speeds ethanol
production
CAMBRIDGE, Mass. (Dec. 7, 2006) — Scientists
from Whitehead Institute and MIT have engineered yeast
that can improve the speed and efficiency of ethanol
production, a key component to making biofuels a significant
part of the U.S. energy supply.
Currently used as a fuel additive to improve gasoline
combustibility, ethanol is often touted as a potential
solution to the growing oil-driven energy crisis. But
there are significant obstacles to producing ethanol.
One is that high ethanol levels are toxic to the yeast
that ferments corn and other plant material into ethanol.
By manipulating the yeast genome, the researchers have
engineered a new strain of yeast that can tolerate elevated
levels of both ethanol and glucose, while producing
ethanol faster than un-engineered yeast.
The work will be reported in the Dec. 8 issue of Science.
Fuels such as E85, which is 85 percent ethanol, are
becoming common in states where corn is plentiful; however,
their use is mainly confined to the Midwest because
corn supplies are limited and ethanol production technology
is not yet efficient enough.
Boosting efficiency has been an elusive goal, but the
researchers, led by Hal Alper, a postdoctoral associate
in the laboratories of MIT chemical engineering professor
Gregory Stephanopoulos and Whitehead Member Gerald
Fink, took a new approach.
The team targeted two proteins that belong to a class
of proteins called transcription factors. These proteins
typically control large groups of genes, regulating
when these genes are turned on or shut off.
When the researchers altered a transcription factor
called the TATA-binding protein, it caused the over-expression
of at least a dozen genes, all of which were found to
be necessary to elicit an improved ethanol tolerance.
As a result, that strain of yeast was able to survive
high ethanol concentrations.
In addition, this altered strain produced 50 percent
more ethanol during a 21-hour period than normal yeast.
Using this approach to engineer similar tolerance traits
in industrial yeast could dramatically impact industrial
ethanol production, a multi-step process in which yeast
plays a crucial role. First, cornstarch or another polymer
of glucose is broken down into single sugar (glucose)
molecules by enzymes, then yeast ferments the glucose
into ethanol and carbon dioxide.
Last year, four billion gallons of ethanol were produced
from 1.43 billion bushels of corn grain (including kernels,
stalks, leaves, cobs and husks) in the U.S., according
to the Department of Energy. In comparison, the U.S.
consumed about 140 billion gallons of gasoline.
Other co-authors on the paper are Joel Moxley, an MIT
graduate student in chemical engineering, and Elke Nevoigt
of the Berlin University of Technology.
The research was funded by the DuPont-MIT Alliance,
the Singapore-MIT Alliance, the National Institutes
of Health and the U.S. Department of Energy.
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