Producing Fuel from Mutated Microbes

With the world’s energy needs rising and the remaining stores of fossil fuels being depleted, sustainable energy is becoming increasingly important. Some estimates suggest that oil reserves mined at current rates will last about 40 years before running dry (1). Yet, nonrenewable fossil fuels make up a large majority of energy consumption and infrastructure (2). Scientists have searched for renewable sources of such fuels, many using mutated bacteria as small energy factories. Although diesel fuel can be produced through bacteria, a process for gasoline production using bacteria has just recently been found. As reported by Nature, researchers Jun Choi and Sang Yup Lee of the Korean Advanced Institute of Science and Technology have recently discovered a technique for producing gasoline using the common bacterium E. coli (3).

The process Choi and Lee created to make these bacteria is complex, but it takes advantage of one important concept: DNA mutation. By changing the sequence of the DNA, they can alter cellular processes and chemical reactions and, in turn, produce gasoline (4).Specifically, DNA contains information which encodes the structures of other large molecules called proteins.  Among the many jobs of a protein is to facilitate chemical reactions in the cell by either pulling apart or pushing together smaller molecules (4).  By manipulating these proteins, Choi and Lee were able to modify chemical reactions to produce the molecules present in gasoline (3).

The molecules in gasoline consist mostly of short-chain alkanes.  An alkane is a molecule made of hydrogen and carbon and formed into chains; the “short” in short-chain means the molecules are between 4 and 12 carbon atoms long (3).

Choi and Lee changed a very specific set of genes in the bacteria. By adding mutant genes and subtracting others from a type of E. coli that already makes certain fat-molecules, Choi and Lee created a pathway which modifies these fatty substances into the necessary short-chain alkanes. They added DNA to encode for new or enhanced versions of proteins essential in this pathway and removed DNA that encoded for proteins destructive to this pathway.

A pathway is simply a string of chemical reactions. The short-chain alkanes are not produced in one step; rather, a series of steps is needed to transform the initial ingredients in the cell to the desired products (3). The molecules begin as sugars, and various proteins add or remove chunks of these ingredients to make the products, like gasoline.

Choi and Lee’s innovation could be an important point in the advancement of renewable energy.  Their final bacterial strain produced up to 580.8 mg/L of short-chain alkanes (3). While this may not be enough to run a car, the development is certainly an important step toward the large-scale manufacturing of such biofuels. And this technique has potential. According to the researchers, the fuel made is similar to the gasoline currently used and, in fact, is superior to many other biofuels in use, and its energy content is 30% higher than ethanol’s (3).  In fact, if these biofuel improvements continue, the future of energy could lie in billions of tiny microbes.

References:

(1): When Will Oil Run Out, Institution of Mechanical Engineers (2013). http://www.imeche.org/knowledge/themes/energy/energy-supply/fossil-energy/when-will-oil-run-out (October 4, 2013).

(2): U.S. Energy Facts Explained, U.S. Energy Information Administration (2013). http://www.eia.gov/energyexplained/index.cfm?page=us_energy_home (October 4, 2013).

(3): Y. J. Choi, S. Y. Lee, Microbial production of short-chain alkanes. Nature (2013), doi: 10.1038/nature12536.

(4): How Genes Work, Genetics Home Reference (2013). http://ghr.nlm.nih.gov/handbook/howgeneswork/protein (October 4, 2013).