Propane is an appealing fuel, easily stored and already used worldwide, but it’s extracted from the finite supply of fossil fuels – or is it? Researchers at Imperial College London and the University of Turku have engineered E. coli bacteria that create engine-ready propane out of fatty acids, and in the future, maybe even sunlight.
When considering the bioproduction of fuels, the researchers looked at the alternatives. Propane is cheaper and easier to condense into liquid than other available gaseous fuels, such as hydrogen. And it’s arguably a better synthetic candidate than liquid fuels which can be detrimental to their living bacterial factories and require purification from the host once produced.
With the premise of producing a fuel that’s more sustainable in a biological host and easier to bring to market, the research team engineered a pathway in E. coli that interrupts the conversion of fatty acids into cell membranes and instead couples naturally unlinked enzymatic processes to manufacture propane.
The recently discovered enzyme aldehyde-deformylating oxygenase (ADO) excited scientists because it provided a catalytic step for the production of hydrocarbons, such as propane, but until now hadn’t been successfully manipulated into a synthetic pathway. In this experiment, researchers amped up the catalyzing power of the enzyme by providing extra electrons to the reaction in the form of reducing agents normally present in photosynthetic organisms (E. coli is not photosynthetic; however, cyanobacteria are).
The bacteria were housed in crimped glass tubes to be able to measure the end products for analysis, and as such, there wasn’t a lot of room for storing the propane end product or controlling the concentration of oxygen. Indeed, the researchers observed that with larger vessels and an increased volume of liquid, the propane production continued for up to six times as long, with a two orders of magnitude increase in propane production.
"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," said Dr Patrik Jones, from the Department of Life Sciences at Imperial College London. "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."