Rochester, New York
March 2, 2007
As the national push for
alternative energy sources heats up, researchers at the
University of Rochester
have for the first time identified how genes responsible for
biomass breakdown are turned on in a microorganism that produces
valuable ethanol from materials like grass and cornstalks.
Waste products such as grass clippings and wood chips—once
thought too difficult to turn into ethanol—may soon be fodder
for hungry, gene-tweaked bacteria.
The findings in today's
Proceedings of the National Academy of Sciences may empower
scientists to engineer ethanol-producing super-organisms that
can make clean-burning fuel from the nation's one billion unused
tons of yearly biomass production.
"This is the first revelation of how a bacterium chooses from
its more than 100 enzymes to break down a particular biomass,"
says David H. Wu, professor in the Department of Chemical
Engineering at the University of Rochester. "Once we know how a
bacterium targets a particular type of biomass, we should be
able to boost that process to draw ethanol from biomass far more
efficiently that we can today."
Ethanol holds the promise of a clean, renewable alternative to
fossil fuels, but deriving it from plants is difficult.
Producing it from corn is the easiest method, but doing so on a
large scale would drive up the price of corn, corn starch, and
even tangential foods like beef, since cows are fed on corn—not
to mention all the energy spent fertilizing, maintaining, and
harvesting a crop like corn. Conversely, deriving ethanol from
plant materials such as the corn stalks and wood chips is
challenging because the plants' cellulose is a very tough
substance to break down, making for an inefficient process.
Wu's technique may prove much more effective than traditional
methods. Instead of using separate steps to break down biomass
into glucose and ferment the glucose into ethanol, as is
currently done, Wu is working on a way to make a bacterium break
down and ferment plant biomass efficiently in just one step.
Wu investigated C. thermocellum, which is a microorganism that
has that ability to turn biomass into ethanol in one step, but
is not used at the industrial scale yet because the first step,
breaking down the plant's cellulose, is much too inefficient.
The key, Wu surmised, is to find out what enzymes the bacterium
uses to accomplish its feat, and then boost its ability to
produce those enzymes. The problem, however, lies in the fact
that C. thermocellum uses more than 100 enzymes, and any of the
millions of combinations of them may be the magic mixture to
break down a particular biomass.
So, Wu decided to make the bacterium do the work for him.
"The bacteria know how to express just the right genes to break
down any particular biomass substrate, and we wanted to know how
they know to turn on and off just the right genes at the right
time to do the trick," says Wu. "We found the bacterium
essentially throws the whole bowl of spaghetti at the wall, sees
what sticks, and then makes a lot of that particular noodle."
C. thermocelllum produces low levels of many of its enzymes at
any one time. When the bacterium comes in contact with wood, for
instance, a few of its enzymes break down some of that wood. A
product of that tiny reaction is a sugar called laminaribiose
that diffuses into the cell. There it deactivates a repressor
for two genes, which wake up and start pumping out the two
triggers the full production of wood-degrading enzymes CelC and
LicA.
Wu's paper shows the first time the triggering pathway for
enzyme production in this bacterium has been revealed, and it
was only possible because C. thermocellum genome was just
recently sequenced, thanks to Wu's collaboration with the U. S.
Department of Energy. With its 100 busy enzymes, the entire
genome had to be observed as a whole, since fiddling with
combinations of two, three, or more enzymes at a time would have
taken "more than our lifetime," Wu says.
Wu is now working to re-engineer C. thermocellum to express an
abundance of particular genes so it can readily and efficiently
produce ethanol from a particular biomass. He's also continuing
the genome-wide search for enzyme combinations that will degrade
and ferment grasses, corn stovers, and even food waste.
"I don't think this is the revolution that makes ethanol a
mainstay," says Wu, "but I believe this is a part of what will
lead to the revolution."
This research, also authored by Wu's graduate students Michael
Newcomb and Chun-Yu Chen, is funded by the U. S. Department of
Energy.
The University of Rochester is one of the nation's leading
private universities. Located in Rochester, N.Y., the University
gives students exceptional opportunities for interdisciplinary
study and close collaboration with faculty through its unique
cluster-based curriculum. Its College of Arts, Sciences, and
Engineering is complemented by the Eastman School of Music,
Simon School of Business, Warner School of Education, Laboratory
for Laser Energetics, Schools of Medicine and Nursing, and the
Memorial Art Gallery. |
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