Common bacteria have been engineered to produce propane, a future source of green fuel.

The research could pave the way to converting solar energy into combustible fuel using photosynthesising bugs, scientists believe.

Propane is already produced as a by-product of natural gas processing. It makes up the bulk of liquid petroleum gas (LPG) which has many applications, from camping stoves to powering motor vehicles.

In the new study, researchers altered Escherichia coli (E.coli) bacteria with certain enzymes so that instead of making cell membranes from fatty acids they generated engine-ready propane.

Lead scientist Dr Patrik Jones, from Imperial College London, said: "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 ultimate goal is to achieve the same result using photosynthesising bacteria, thereby converting solar energy directly into chemical fuel.

Algae, which photosynthesise, can already be used to make biodiesel but the costly and wasteful process is not commercially viable.

Results from the study, funded by the European Research Council, appear in the journal Nature Communications.

Dr Jones added: "At the moment, we don't have a full grasp of exactly how the fuel molecules are made, so we are now trying to find out exactly how this process unfolds. I hope that over the next five to 10 years we will be able to achieve commercially viable processes that will sustainably fuel our energy demands."