March 19,
2007
Genome Sequencing Reveals a Key to Efficient Ethanol
Production
A research breakthrough by David Wu, professor of
chemical engineering, could lead to novel ways of producing the alternative
fuel ethanol from abundant materials such wood chips and grass clippings.
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.
David Wu, professor in the Department of Chemical
Engineering, has for the first time identified how genes responsible for
biomass breakdown are turned on in a microorganism that produces valuable
ethanol from material like grass and cornstalks.
The findings may empower scientists to engineer
ethanol-producing super-organisms that can make clean-burning fuel from the
nation’s 1 billion unused tons of yearly biomass production.
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.
“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,” says Wu.
When the bacterium comes in contact with wood, for
instance, a few of its enzymes break down some of that wood, producing a
sugar that triggers the full production of wood-degrading enzymes.
Wu’s paper, published in the Proceedings of the National Academy of Sciences, 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.
“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.”
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