Bacteria brews biofuel with potential to replace high-energy rocket fuel

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Georgia Tech researchers Pamela Peralta-Yahya and Stephen Sarria examine the production of the hydrocarbon pinene in laboratory test tubes (Photo: Georgia Tech/Rob Felt)

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Researchers at the Georgia Institute of Technology and the US Department of Energy’s Joint BioEnergy Institute have engineered a bacterium that could yield a new source of high-energy hydrocarbon fuel for rocketry and other aerospace uses.

High-energy, specific-use hydrocarbon fuels such as JP-10 can be extracted from oil, along with more commonly used petroleum fuels, but supplies are limited and prices are high – approaching US$7 per liter. That’s where the new bacterium, engineered by Georgia Tech scientists Stephen Sarria and Pamela Peralta-Yahya, could come in.

By introducing enzymes into the strain of E. coli bacterium a reaction is developed that yields pinene, a cyclic hydrocarbon related to isoprene – a major ingredient of pine resin and a vital precursor to a biofuel that offers an energy density comparable to JP-10.

The biofuel is then produced by "dimerising," or linking together, two molecules of pinene via chemical catalysis.

"We have made a sustainable precursor to a tactical fuel with a high energy density,” says Peralta-Yahya, an assistant professor in the School of Chemistry and Biochemistry and the School of Chemical and Biomolecular Engineering at Georgia Tech. “We are concentrating on making a ‘drop-in’ fuel that looks just like what is being produced from petroleum and can fit into existing distribution systems."

Much research has gone into more efficient ways of producing ethanol and biodiesel fuels, yet comparatively little work has been done on replacements for high-energy fuels. And while the Georgia Tech research has yielded impressive results, there are obstacles to be overcome before its process can be made competitive with the manufacture of petroleum-based JP-10.

One problem is that the action of the enzymes on the bacterium becomes inhibited once the yield of pinene solution reaches a particular concentration in its glucose growth medium.

"Now we need either an enzyme that is not inhibited at high substrate concentrations, or a pathway that can maintain low substrate concentrations throughout the run," says Peralta-Yahya. "Both of these are difficult, but not insurmountable, problems. If you are trying to make an alternative to gasoline, you are competing against less than $1 per liter. That requires a long optimization process. Our process will be competitive with $7 per liter in a much shorter time.”

The team's research appears in the journal ACS Synthetic Biology.

Source: Georgia Tech

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