For the first time, researchers at the UCLA Henry Samueli School of Engineering and Applied Science have successfully pushed nature beyond its limits by genetically modifying Escherichia coli, a bacterium often associated with food poisoning, to produce unusually long-chain alcohols essential in the creation of biofuels.
"Previously, we were able to synthesize long-chain alcohols containing five carbon atoms," said James Liao, UCLA professor of chemical and biomolecular engineering. "We stopped at five carbons at the time because that was what could be naturally achieved. Alcohols were never synthesized beyond five carbons. Now, we've figured out a way to engineer proteins for a whole new pathway in E. coli to produce longer-chain alcohols with up to eight carbon atoms."
The new protein and metabolic engineering method developed by Liao and his research team is detailed in the Dec. 30 issue of Proceedings of the National Academy of Sciences. The paper is currently available online.
Longer-chain alcohols, with five or more carbon atoms, pack more energy into a smaller space and are easier to separate from water, making them less volatile and corrosive than the commercially available biofuel ethanol. The greater the number of carbon atoms, the higher the density of the biofuel. Ethanol, most commonly made from corn or sugarcane, contains only two carbon atoms.
Organisms typically produce a large number of amino acids, which are the building blocks of proteins. In their research, Liao's team examined the metabolism of amino acids in E. coli and changed the metabolic pathway of the bacterium by inserting two specially coded genes. One gene, from a cheese-making bacterium, and another, from a type of yeast often used in baking and brewing, were altered to enable E. coli's amino acid precursor, keto acid, to continue the chain-elongation process that ultimately resulted in longer-chain
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University of California - Los Angeles