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Sustainable Energy

A Novel Way to Cut the Cost of Advanced Biofuels

Modifying a gene in plants makes it far easier to process biomass to make fuel.

Cellulosic ethanol is too expensive to compete with fossil fuels.

A novel genetic modification to plants could make advanced biofuels more competitive with fossil fuels, according to a study published this week in the journal Science. The modification could achieve this by rendering an expensive step in making such biofuels unnecessary.

red dyed cross section of a stem
Biofuel blocker: Lignin, dyed red in this cross section of a stem, makes it hard to turn biomass into fuel.

Currently almost all ethanol production comes from the sugar and starch in sugarcane and corn grain. Producing biofuels from biomass remains too expensive to be competitive, partly because the current method for freeing up the cellulose from lignin, the substance that gives plants woody properties, is to treat biomass with hot acid. This step is expensive in part because it requires specialized equipment that can withstand the acid.

In the new work, researchers discovered that when they eliminated a key gene responsible for how lignin is formed, plants produced far less of the substance. They then showed that 80 percent of the cellulose in these modified plants could be converted to sugar without treating them with acid. In comparison, in untreated, ordinary plants, only 18 percent of the cellulose could be converted.

The work is still far from commercial application. The researchers have yet to show that the approach works with the kind of plants that will be used for making biofuels, such as switchgrass or poplar, but they’ve found similar lignin-producing steps in these plants, suggesting that it will be possible to transfer the approach.

Another challenge is that the genetic modification produces shorter plants with less biomass, which would lead to lower biofuel yields. The problem is that lignin is a crucial structural material, and decreasing it too much affects the way plants grow. But researchers at Lawrence Berkeley National Laboratory recently demonstrated a way to reduce lignin content in some parts of the plant, but not others, thereby allowing the plant to grow normally. Woet Boerjan, a professor at VIB, a research institute in Belgium, and one of the researchers involved in the new work, says a similar approach could work in their case.

Meanwhile, companies have been developing their own ways around the acid treatment. Ceres, based in Thousand Oaks, California, says it has modified plants, including reducing lignin content. It’s tested the approach in labs, and is now growing crops that it will harvest and test this fall. Richard Hamilton, Ceres’s CEO, says eliminating the acid pre-treatment could reduce the amount of enzymes needed to convert cellulose into sugar, and could cut as much as $1 per gallon from the cost of making ethanol from biomass, a large reduction for an industry that hopes to reach costs of $3 to $4 per gallon.

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