Efficient Biofuel Made From Genetically Modified E. Coli Bacteria

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.

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.

A new strategy has been developed by UCLA professor of chemical and biomolecular engineering James Liao, postdoctoral fellow Shota Atsumi and visiting professor Taizo Hanai.

"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 from glucose, a renewable carbon source, including isobutanol, 1-butanol, 2-methyl-1-butanol, 3-methyl-1-butanol and 2-phenylethanol.

This strategy leverages the E. coli host's highly active amino acid biosynthetic pathway by shifting part of it to alcohol production. In particular, 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.

"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, and there is no advantage for them to do so. 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.

"Given that part of UCLA's mission is to transfer technologies to the commercial sector to benefit the public, we are excited at the prospect that this UCLA-developed technology may play a key role in addressing climate change and energy independence," said Earl Weinstein, assistant director of the UCLA Office of Intellectual Property. "It has been a pleasure to work with the team at Gevo on this deal, and we look forward to an ongoing relationship with them".

"This discovery leads to new opportunities for advanced biofuel development," said Patrick Gruber, Gevo's chief executive officer. "As the exclusive licensee of this technology, we can further our national interests in developing advanced renewable resource-based fuels that will help address the issues of climate change and future energy needs while creating a significant competitive advantage."

Liao has joined Gevo's scientific advisory board. In this role, he will continue to provide technical oversight and guidance during the commercial development of this technology.

"Dr. Liao's input will be invaluable as we scale up the commercial applications made possible by this breakthrough in technology and bring advanced biofuels to market," said Matthew Peters, chief scientific officer of Gevo.

Full details of the research appear in the Jan. 3 issue of the journal Nature.

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.