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Scientists engineer sugarcane, switchgrass to produce biofuelsScientists engineer sugarcane, switchgrass to produce biofuels

Research aims to improve non-food biofuel crops to better extract precursors for biodiesel and ethanol production.

Tim Lundeen 1

April 5, 2017

4 Min Read
Scientists engineer sugarcane, switchgrass to produce biofuels
Researchers extract juice from sugarcane that has been engineered to produce oil for biodiesel in addition to the plant's sugar that is used for ethanol production.Credit: Kathryn Faith/University of Illinois

More research is being conducted to improve non-food biofuel crops to better extract precursors for biodiesel and ethanol production.

This week, the University of Illinois described research into genetically engineering sugarcane to produce oil for biodiesel that also increased the plant's sugar content, which can be used for ethanol production. Meanwhile, a researcher at the University of Wisconsin-Milwaukee is working on a genetic sterility switch to prevent enhanced switchgrass varieties from cross-pollinating with wild-type switchgrasses.

According to the University of Illinois, the dual-purpose sugarcane crops are predicted to be more than five times more profitable per acre than soybeans and two times more profitable than corn. More important, sugarcane can be grown on marginal land in the Gulf Coast region that does not support good corn or soybean yields.

"Instead of fields of oil pumps, we envision fields of green plants sustainably producing biofuel in perpetuity on our nation's soil, particularly marginal soil that is not well suited to food production," said Stephen Long, the Gutgsell endowed professor of plant biology and crop sciences. Long leads the research project "Plants Engineered to Replace Oil in Sugarcane & Sweet Sorghum" (PETROSS) that has pioneered this work at the Carl R. Woese Institute for Genomic Biology at the University of Illinois.

"While fuel prices may be considered low today, we can remember paying more than $4/gal. not long ago," Long said. "As it can take 10-15 years for this technology to reach farmers' fields, we need to develop these solutions to ensure our fuel security today and as long as we need liquid fuels into the future."

Published in Biocatalysis & Agricultural Biotechnology, this paper analyzes the project's first genetically modified sugarcane varieties. Using a juicer, the researchers extracted about 90% of the sugar and 60% of the oil from the plant; the juice was fermented to produce ethanol and later treated with organic solvents to recover the oil. The team has patented the method used to separate the oil and sugar.

"The oil composition is comparable to that obtained from other feedstocks like seaweed or algae that are being engineered to produce oil," said co-author Vijay Singh, director of the university's Integrated Bioprocessing Research Laboratory.

"We expected that as oil production increased, sugar production would decrease, based on our computer models," Long said. "However, we found that the plant can produce more oil without loss of sugar production, which means our plants may ultimately be even more productive than we originally anticipated."

'Switch' for switchgrass

Switchgrass has been lauded as a promising source of biofuels with multiple advantages over current favored options, including corn. Genetically modifying switchgrass could boost crop yields and its commercial viability.

However, to realize that potential requires one small tweak: a genetic sterility switch that prevents the modified grass from contaminating the genes of nearby unmodified grasses. University of Wisconsin-Milwaukee associate professor of biological sciences Dazhong “Dave” Zhao hopes to build that switch.

Switchgrass is an attractive biofuel feedstock because it can grow on marginal lands with little agricultural value. It also requires less chemical fertilizer than corn, currently the dominant feedstock source for ethanol that's mixed into unleaded gasoline.

In addition to being a low-input and fast-growing crop, switchgrass can survive for 10 years or more, while corn must be sown at the start of each growing season.

To make biofuel production more sustainable, Zhao and postdoctoral researcher Jian Huang are tackling the main obstacle that has kept genetically modified switchgrass off the commercial market: the possibility that lab-engineered genes could escape human control by mixing with genes of wild-growing grasses, which might interrupt natural processes in unpredictable ways.

“Completely eliminating both male and female fertility is the only fail-safe way to prevent gene flow,” Zhao said.

Under current federal regulations, only genetically modified grasses that are absolutely sterile in the lab can enter field trials. That’s where researchers determine whether sterility and other introduced properties can be maintained long-term in real-world conditions.

Zhao said he hopes to create sterile switchgrass by introducing a fusion gene into its reproductive cells using a harmless bacterium as a delivery vehicle.

Zhao is testing this method in Brachypodium distachyon, a model grass very similar to switchgrass. He has already demonstrated that his fusion gene, for which he filed a patent application, works well in tobacco and Arabidopsis, a flowering plant commonly used as the first test case for genetic modifications.

If the fusion gene works well in the model grass, Zhao plans to collaborate with U.S. Department of Agriculture scientists on testing it in switchgrass. Success in the lab could lead to funding for field trials and eventual commercialization.

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