The process uses a fungus and E coli bacteria to turn the tough plant material into a biofuel that matches gasoline’s properties better than ethanol.
“We’re hoping that biofuels made in such an efficient way can eventually replace current petroleum-based fuels,” said Xiaoxia “Nina” Lin, assistant professor of chemical engineering, and leader of the research at the University
Gallon for gallon, isobutanol gives off 82 per cent of the heat energy gasoline provides when burned, compared to ethanol’s 67 per cent. Ethanol also has a tendency to absorb water, corroding pipelines and damaging engines, but isobutanol doesn’t mix easily with water. While ethanol serves as a mixer in the gasoline infrastructure today, many researchers argue that isobutanol could be a replacement.
While the technology currently uses corn stalks and leaves, it should also be able to process other agricultural byproducts and forestry waste.
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. The scientists put both microbe species into a bioreactor with 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 litre 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 per cent of the theoretical maximum.
The harmonious coexistence of the fungi and bacteria, with stable populations, was a key success of the experiment.
The team is now trying to improve the energy conversion rate and increase the tolerance of the T reesei and E coli to isobutanol. The fuel is toxic, but higher concentrations will drive down the cost of isolating the fuel.
By engineering the bacteria differently, they believe their system could produce a variety of petroleum-based chemicals in a sustainable way.
A paper on this research, Design and characterization of synthetic fungal-bacterial consortia for direct production of isobutanol from cellulosic biomass was published in The Proceedings of the National Academy of Sciences. The work was funded by the National Science Foundation, the Department of Energy, and the U-M Office of the Vice President for Research. The university is seeking commercialisation partners to help bring the technology to market.