Researchers use bacteria to generate biofuels

By Matthew Chin

Escherichia coli (E. coli) bacteria may be the key to more efficiently synthesizing and mass producing biofuels. Researchers at the UCLA Henry Samueli School of Engineering and Applied Science have developed a new method for producing next-generation biofuels by genetically modifying this common bacteria.

James Liao, professor of chemical and biomolecular engineering, postdoctoral fellow Shota Atsumi and visiting professor Taizo Hanai report on their research in the Jan. 3 issue of the journal Nature.

Concerns about long-term fossil fuel availability, coupled with environmental problems resulting from their production and use, have spurred increased efforts to synthesize biofuels from renewable resources.

BYPASSING ETHANOL'S LIMITATIONS

Biofuels, like commercially available ethanol, are produced from agricultural products such as corn, sugarcane or waste cellulose. Ethanol, however, has limitations: it is not as efficient as gasoline and must be mixed with gas for use as a transportation fuel. It also tends to absorb water from its surroundings, making it corrosive and preventing it from being stored or distributed in existing infrastructure without modification.

"Higher-chain" alcohols have energy densities close to gasoline, are not as volatile or corrosive as ethanol, and do not readily absorb water. Furthermore, branched-chain alcohols, such as isobutanol, have higher-octane numbers, resulting in less knocking in engines. Isobutanol or C5 alcohols have never been produced from a renewable source with yields high enough to make them viable as a gasoline substitute.

"These alcohols are typically trace byproducts in fermentation," Liao said. "To modify an organism to produce these compounds usually results in toxicity in the cell. We bypassed this difficulty by leveraging the native metabolic networks in E. coli but altered its intracellular chemistry using genetic engineering to produce these alcohols."

The research team modified key pathways in E. coli to produce several higher-chain alcohols. The research team achieved high-yield, high-specificity production of isobutanol from glucose.

This new strategy opens an unexplored frontier for biofuels production, both in coli and in other microorganisms.

RESULTS SURPRISING AND PROMISING

"The ability to make these branched-chain higher alcohols so efficiently is surprising," Liao said. "Unlike ethanol, organisms are not used to producing these unusual alcohols ... The fact that they can be made by E. coli is even more surprising, since E. coli is not a promising host to tolerate alcohols.

"These results mean that these unusual alcohols in fact can be manufactured as efficiently as what evolved in nature for ethanol. Therefore, we now can explore these unusual alcohols as biofuels and are not bound by what nature has given us."

UCLA has licensed the technology through an exclusive royalty-bearing license to Gevo Inc., a Pasadena, Calif.-based company founded in 2005 and dedicated to producing biofuels. The research was supported in part by the UCLA–Department of Energy Institute for Genomics and Proteomics and the UCLA–NASA Institute for Cell Mimetic Space Exploration.