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Bioengineered Microbe to Convert, Recycle Biofuel Waste

Miscanthus (Oak Ridge National Lab)

Miscanthus (Oak Ridge National Lab)

Plant biologists at Texas A&M AgriLife Research in College Station are creating a bioengineered microbe to convert the waste from biofuel production into more biofuel. The project led by plant pathologist Joshua Yuan is funded by a $2.4 million grant from the U.S. Department of Energy.

Yuan and colleagues at AgriLife are developing a genetically engineered microorganism that breaks down the lignin left over from processing of cellulosic biofuel feedstocks, such as switchgrass or miscanthus. Lignin remains after the sugar, or cellulose, in a plant has been converted into ethanol. International Lignin Institute estimates 40 to 50 million tons of lignin are produced worldwide as products each year.

Biofuel referies account for about 60 percent of the excess lignin. One of the reasons for the accumulation of waste lignin is its difficulty in processing and disposal. “It’s resistant to degradation and very strong,” says Yuan. “It can be burned, but there is so much that burning all of it would create an environmental hazard.”

These properties call for the AgriLife researchers to engineer a new biological process to deal with the excess lignin from biofuels. In their work so far, Yuan and colleagues identified the Rhodococcus bacteria, as a potential starting point for this engineered microorganism. Various Rhodococcus strains are already in use for metabolizing hydrocarbons, such as petroleum and its derivatives, for industrial processes and environmental clean-ups.

In their research, Yuan’s team will aim for developing an engineered form of Rhodococcus, a largely benign bacteria, to turn lignin into lipids, a type of fat, which can be used to produce biodiesel. Yuan says the project is expected to result in a process for converting at least 40 percent of excess lignin.

“The conversion will allow more complete use of carbon in biomass and result in the mitigation of more than 20 million tons of carbon dioxide,” notes Yuan. “It will also provide another major type of feedstock for biodiesel production, potentially contributing about 10 percent of the total advanced biofuel production.” Yuan adds that the process could, in addition, simplify waste treatment and help make biofuel refineries more profitable.

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