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engineering and leader of the research. Isobutanol could function as an effective substitute for gasoline – isobutanol releases about 82% of the heat energy that gasoline does when burned, as compared to the 67% that ethanol does. And, isobutanol doesn't possess the same significant drawbacks that ethanol does because it doesn't possess ethanol's 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 the entire infrastructure in use today were completely replaced, isobutanol could replace gasoline as is – no new infrastructure needed. 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 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 november 2013 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. " lot of times, one species will dominate A 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 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 working to improve the energy conversion rate and to improve the abilities of both T. reesei and E. coli to tolerate exposure to isobutanol. "We're really excited about this technology," Minty explained. "The US 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." n www.resourceworld.com 59