Transgenic Switchgrass Improves Biofuel Yield

Switchgrass (Agricultural Research Service/USDA)

Plant engineering by The Samuel Roberts Noble Foundation in Ardmore, Oklahoma and fermentation research by Oak Ridge National Laboratory in Tennessee have led to new lines of native perennial prairie grass  that can make the production of cellulosic ethanol more economical. The researchers published their findings this week in in the Proceedings of the National Academy of Sciences.

In the paper, researchers describe their transgenic version of switchgrass as one that produces more than one-third more ethanol by fermentation than conventional switchgrass. This improved plant feedstock will be able to generate more biofuel per acre, benefiting not only ethanol producers, but also the growers and their communities.

Switchgrass holds great promise as a bioenergy feedstock because it is a native perennial plant, grows with high yields and requires little nitrogen and water. The barriers have arisen in the plant’s natural defenses against insects, fungus, and the weather.

For years researchers have sought better ways to reduce the plant’s defense system, while keeping it robust enough to survive. A team led by Zeng Yu Wang of The Samuel Roberts Noble Foundation genetically altered a cellular component in the Alamo variety of switchgrass. This change decreased the plant’s structural “glue,” called lignin, by about one-eighth.

“The presence of lignin in plant cell walls interferes with the fermentation to produce biofuels,” says Wang, who noted that enzymes are the single largest processing cost component for bioconversion of biomass after the biomass itself.

At the Oak Ridge Lab, Jonathan Mielenz and his team found this transgenic variety of switchgrass to be more easily converted to biofuels under milder conditions and with much lower costly additions during fermentation. The research showed that the lines require less severe pretreatment and 300–400 percent lower enzyme dosages for equivalent product yields using simultaneous sugar production and fermentation with yeast.

According to the authors, the new lines can increase ethanol production up to 38 percent, with the potential to lower processing costs for fermentation-driven biomass fuels and chemicals.

Read more: Genetic Researchers Identify Enzymes for Biofuels

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