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Isobutanol From Cornstalks And Plant Leaves — Fungus And Bacteria Pairing Converts Waste Plant Material Into High-Performance Biofuel

Isobutanol — a high-performance biofuel that closely matches the properties of gasoline — can be produced from waste plant materials through the combined actions of a common fungus and a common bacteria, according to new research from the University of Michigan. When paired up together, the fungus Trichoderma reesei, and the bacteria Escherichia coli, can effectively create the biofuel isobutanol from materials such as cornstalks and plant leaves.

While the production of a useful biofuel is impressive enough, the researchers think that the same principle used to produce the biofuel could be used to produce other useful chemicals, such as plastics.

“We’re hoping that biofuels made in such an efficient way can eventually replace current petroleum-based fuels,” stated Xiaoxia “Nina” Lin, assistant professor of chemical engineering and leader of the research.

And isobutanol could indeed function as a relatively effective substitute for gasoline — isobutanol releases just around 82% of the heat energy that gasoline does when burned, as compared to the 67% that ethanol does. And, perhaps more importantly, isobutanol doesn’t possess the same significant drawbacks that ethanol does — in particular, it doesn’t possess ethanol’s unfortunate tendency to absorb water, and thus doesn’t damage conventional engines and pipelines in the same way that pure ethanol does. So, while pure ethanol would only be a viable replacement for gasoline if all of the infrastructure in use today was completely replaced, isobutanol cold simply replace gasoline as is — no new infrastructure needed.

"The biofuel isobutanol, in the vial, was produced by a microbe community feeding on corn stalks and leaves or switchgrass, shown in the flasks behind." Image Credit: Joseph Xu

“The biofuel isobutanol, in the vial, was produced by a microbe community feeding on corn stalks and leaves or switchgrass, shown in the flasks behind.”
Image Credit: Joseph Xu

The press release from the University of Michigan has more:

Equally important, this system makes isobutanol from inedible plant materials, so fuel production won’t drive up food costs. Lin’s team used corn stalks and leaves, but their ecosystem should also be able to process other agricultural byproducts and forestry waste. While much previous research has focused on trying to create a “superbug” that could tackle the whole job of processing waste plant materials into biofuels, Lin and her colleagues argue that a team of microbial specialists can do better.

The fungus Trichoderma reesei is already very good at breaking down tough plant material into sugars. Escherichia coli, meanwhile, is relatively easy for researchers to genetically modify. James Liao’s lab at the University of California-Los Angeles provided E. coli bacteria that had been engineered to convert sugars into isobutanol. The Lin group put both microbe species into a bioreactor and served up corn stalks and leaves. Colleagues at Michigan State University had pre-treated the roughage to make it easier to digest.

The fungi turned the roughage into sugars that fed both microbe species with enough left over to produce isobutanol. The team managed to get 1.88 grams of isobutanol per liter of fluid in the ecosystem, the highest concentration reported to date for turning tough plant materials into biofuels. They also converted a large proportion of the energy locked in the corn stalks and leaves to isobutanol — 62% of the theoretical maximum. The harmonious coexistence of the fungi and bacteria, with stable populations, was a key success of the experiment.

“A lot of times, one species will dominate the culture and the other will die off,” stated Jeremy Minty, first author of the new paper. “This is a common problem when you’re trying to create these systems.”

But obviously there are some significant advantages to such systems. “You can put everything in one pot,” Lin explained. “The capital investment will be much lower, and also the operating cost will be much lower, so hopefully this will make the whole process much more likely to become economically viable.”

The researchers are now be working to improve the energy conversion rate, and also to improve the abilities of both T. reesei and E. coli tolerate exposure to isobutanol.

“We’re really excited about this technology,” Minty explained. “The U.S. has the potential to sustainably produce 1 billion tons or more of biomass annually, enough to produce biofuels that could displace 30% or more of our current petroleum production.”

The new research was just published in the Proceedings of the National Academy of Sciences.

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Written By

James Ayre's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy.


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