In their Nature magazine article, researchers from the University of Turku (Finland) and Imperial College (United Kingdom) described a new metabolic pathway for producing propane from Escherichia coli (E.coli).
In "normal" E.coli, a biological process exists that turns fatty acids into cell membranes. In their September 2014 article, Dr. Pauli Kallio, et. al. describe a way to shift this pathway so that the bacteria produce propane instead. This shift is achieved by using enzymes to channel the fatty acids that previously made cell walls and, instead, use them to make propane that is engine-ready.
Three enzymes are used in this process:
1. A new variant of thioesterase - specifically targets fatty acids and releases them from natural process
2. A bacterial enzyme called CAR - used to convert butyric acid into butyraldehyde
3. A recently discovered enzyme called aldehyde-deformylating oxygenase (ADO) - known to naturally create hydrocarbons (including propane). Cccording to Dr. Pauli Kallio, et. al., the discovery of this enzyme was key in developing their method for producing propane using E.coli.
Propane is the bulk component of liquid petroleum gas. LP gas is used around the world, for activities including cooking and heating in India and some rural areas of the United States. Used in its gas form, but frequently stored as a more energy-dense liquid, LP gas is perhaps best known for its role on campsites and outdoor BBQ grills. LP gas is also used as a gasoline alternative ("autogas") in motor vehicles.
Dr. Pauli Kallio, et. al. chose to target propane production in their research because it could easily escape the cell as a gas but required relatively little energy to liquify. In turn, this fuel is somewhat easy to transport, store and use.
The process of modifying E.coli to produce propane is still in the early stages of development. But, according to Dr. Patrik Jones of the Department of Life Sciences at Imperial College (and a co-author on this paper):
Although this research is at a very early stage, our proof of concept study provides a method for renewable production of a fuel that previously was only accessible from fossil reserves. Although we have only produced tiny amounts so far, the fuel we have produced is ready to be used in an engine straight away. This opens up possibilities for future sustainable production of renewable fuels that at first could complement, and thereafter replace fossil fuels like diesel, petrol, natural gas and jet fuel.
The scientists ultimately want to insert this engineered propane-producing system into photosynthetic bacteria. The system would then be capable of directly converting solar energy into a chemical fuel that is engine-ready. No processing or refining required.
Reference: Pauli Kallio, András Pásztor, Kati Thiel, M. Kalim Akhtar, and Patrik R. Jones. An engineered pathway for the biosynthesis of renewable propane. Nature Communications 5 Article number: 4731 doi:10.1038/ncomms5731 Published 02 September 2014 (link)