Scientists are one step closer to filling your car's tank with grass clippings and willow trees. A new genetically engineered strain of yeast can devour the tough parts of plants as readily as the sweet sugars.
The new yeast could allow production of large amounts of ethanol from fast growing grasses and trees, as well as residues from sugar cane and other crops. The yeast was engineered by researchers at the University of Illinois, the Lawrence Berkeley National Laboratory, the University of California and the energy company BP.
The tough parts of plants are made up of a sugar called cellulose. Cellulose is made up of smaller sugars, particularly glucose and xylose. Yeast love glucose, but most strains can't eat xylose. Those that can ferment the xylose do so slowly and only after the glucose is gone.
"It's like giving meat and broccoli to my kids. They usually eat the meat first and the broccoli later." said Yong-Su Jin of the University of Illinois and one of the researchers who developed the new yeast.
The new strain can ferment both glucose and xylose at the same time, which reduces reaction time by half. It also increases cellulose fermentation efficiency by at least 20 percent.
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To do this, the team made several changes to the DNA of the yeast.
First, they gave the yeast a cellobiose transporter. Cellobiose is a part of the plant's cell wall. In earlier forms of cellulose fermentation, an expensive enzyme had to be added to break the cellobiose down. Now the yeast sucks the cellobiose inside its cells and has its own enzyme to break the chemical down.
Since cellobiose is made up of two glucose molecules, it provides a rich energy source.
The biologists also added three genes from another species of yeast, Picchia stipitis. These genes allow the yeast to digest xylose.
Another feat of genetic engineering fixed a bottleneck in the xylose to ethanol production pathway. The scientists added an artificial enzyme to reduce byproduct production.
The researchers published their findings in the Proceeding of the National Academy of Sciences.
Improving the industrial production of ethanol could have significant economic benefits.
"We don't have to do two separate fermentations," Jin said in a University of Illinois press release. "We can do it all in one pot. And the yield is even higher than the industry standard. We are pretty sure that this research can be commercialized very soon."
If it is commercialized soon, it could reduce our “pain at the pump.”
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Any car can run on a 10 percent ethanol (E10) mixture, even if it isn't a “FlexFuel” vehicle. Many cars can use even higher amounts. Improving ethanol production in the U.S. could lower fuel costs and emissions.
Brazil gets a large amount of its transport fuel from sugar cane ethanol. Fermenting cellulose would allow them to use the sugar cane left overs (bagasse) as well. It also makes the use of wood and grass more feasible.
Improving cellulosic ethanol production may allow the commercial scale fermentation of ethanol from agricultural left overs. But some scientists caution against the use of crop residues, like corn stalks and husks. Stalks and husks are too valuable in preventing erosion and improving soil quality to take them off the farm.
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Some also worry that devoting more corn and sugar cane to ethanol production could cause food shortages. Though the food crisis of 2008 was largely caused by market speculation driving up prices, ethanol production received some of the blame for highly priced corn.
No one eats cellulose, so by producing more ethanol from cellulose, there is less conflict of interest.
Also, since much of the carbon in plant matter is absorbed from the air, when ethanol made from plants is burned there is a lower increase in net carbon dioxide in the atmosphere than when petroleum products are burned.
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