A gas pump in Sao Paolo, Brazil featuring both regular gas and ethanol. Source: Wikipedia
The United States has developed infrastructure that supports the use of hydrocarbon fuels. Billions of dollars have been spent creating pipelines, storage, and end products that function specifically with these fuels. With the green movement, there has been a push to create more ‘environmentally friendly’ biofuels. Scientists have successfully designed biofuels, such as alcohols and biodiesels, but none fit ideally into the existing hydrocarbon-based systems. The varying structural and chemical make-ups of biofuels cause inefficiency in their use and problems with their transport and storage, making a blend high in hydrocarbon fuel still necessary.
Until now, no biofuel could replace hydrocarbons. Scientists at the University of Exeter have recently engineered E. coli to produce biofuels of the same structure and chemical composition as hydrocarbon fuels. This technology is not yet ready for mass commercialization or even for producing more than a few drops of biofuel, but the methods now exist to create a biofuel that can fully replace hydrocarbon fuels and exist within the current infrastructure [1].
On a molecular level, hydrocarbon fuels consist of linear and branched chains of alkanes and alkenes. To reproduce this in E. coli, new synthetic metabolic pathways had to be created to generate the exact chain lengths found in mineral-based hydrocarbon fuels. Normally, E. coli metabolize sugars to create fats for cell use. To take advantage of this natural mechanism, scientists engineered a new metabolic pathway that used the free fatty acids as substrates for production of the desired linear and branched alkane chains. The scientists co-expressed elements of other organisms’ metabolic systems with the natural E. coli metabolic complexes to control the structure of the products. The scientists also genetically engineered the experimental E. coli to include a compound to stop chain production at the desired length and a separate complex to grow branched alkanes instead of the natural linear alkanes. Finally, the scientists also added genetic instructions to code for extra fatty acids for use in the existing alkane synthesis pathway [2].
This achievement offers a way to produce fossil fuels from biological sources that structurally and chemically match the hydrocarbon fossil fuels in use today. Using biological sources for fuel production reduces carbon dioxide emissions significantly. Still, consumer use of biofuels in automobile engines and other modes of transportation will release greenhouse gases. The research group expects the E. coli biofuels to have a zero net effect on carbon dioxide emissions and environmental health.
A drawback to the genetically-engineered E. coli is that while they can now create fuels that can be used like mineral-based hydrocarbon fuels, they only produce miniscule amounts. In an interview with US News, the lead researcher admitted that he is currently attempting to create enough fuel to “fill a jar” [3]. Commercial use of his technique is still far in the future.
Ultimately, the achievement of genetically engineering E. coli to create fuel identical to fuel currently used is a landmark both for biochemists and environmentalists. This is the first biofuel that could be put into the current infrastructure without requiring dramatic changes. Even though commercialization of the production method is still at least a decade away, the innovation will continue to be applied to E. coli to improve yield of fuel and to other organisms to investigate other efficient ways of producing biofuel.
References:
1. Special E. coli bacteria produce diesel on demand (2013). Available at http://www.sciencedaily.com/releases/2013/04/130422154911.htm (28 April 2013).
2. T. P. Howard et al., Proc. Natl. Acad. Sci. U.S.A., 1-6 (2013).
3. J. Koebler, E. coli-Produced Diesel Could Power Cars (2013). Available at http://www.usnews.com/news/articles/2013/04/22/e-coli-produced-diesel-could-one-day-power-cars (28 April 2013).