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.