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Renewable fossil fuel alternative made using bacteria

2 September 2014

In a new study published in the journal Nature Communications, researchers have engineered the harmless gut bacteria Escherichia coli (E. coli) to generate renewable propane.

The development is a step towards commercial production of a source of fuel that could one day provide an alternative to fossil fuels.

bacteria

Propane is an appealing source of cleaner fuel because it has an existing global market. It is already produced as a by-product during natural gas processing and petroleum refining, but both are finite resources. In its current form it makes up the bulk of LPG (liquid petroleum gas), which is used in many applications, from central heating to camping stoves and conventional motor vehicles.

The team of scientists from the University of Turku in Finland – including Dr Kalim Akhtar who is now at UCL – and Imperial College London used E. coli to interrupt the biological process that turns fatty acids into cell membranes and instead channel it toward the production of an engine-ready biofuel, in this case propane.

This was achieved by engineering a metabolic pathway that consisted of three key enzymes: i) a thioesterase to produce butyric acid, ii) a carboxylic acid reductase (CAR) to convert butyric acid into butyraldehyde, and iii) an aldehyde-deformylating oxygenase (ADO) to form the final product, propane.

This study is yet another prime example of how we’re moving very swiftly from biological discovery to translational research. It highlights how fundamental biological processes can be utilised to develop potentially benign technologies, ones that could be used to benefit both humankind and the environment.

Dr Kalim Akhtar

Previous attempts to use the ADO enzyme have proved elusive as scientists have been unable to harness the natural power of the enzyme to create cleaner fuel. But the scientists behind this European Research Council funded study discovered that by stimulating ADO with electrons, they were able to substantially enhance the catalytic capability of the enzyme and ultimately produce greater levels of propane.

Their ultimate goal is to insert this engineered system into photosynthetic bacteria, so as to one day directly convert solar energy into chemical fuel.

Joint corresponding author Dr Kalim Akhtar (UCL Biochemical Engineering), said: “This study is yet another prime example of how we’re moving very swiftly from biological discovery to translational research. It highlights how fundamental biological processes can be utilised to develop potentially benign technologies, ones that could be used to benefit both humankind and the environment.”

Lead author Dr Patrik Jones (Department of Life Sciences, 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 scientists chose to target propane because it can easily escape the cell as a gas, yet requires little energy to transform from its natural gaseous state into a liquid that is easy to transport, store and use.

“Fossil fuels are a finite resource and as our population continues to grow we are going to have to come up with new ways to meet increasing energy demands. It is a substantial challenge, however, to develop a renewable process that is low-cost and economically sustainable.  At the moment algae can be used to make biodiesel, but it is not commercially viable as harvesting and processing requires a lot of energy and money. So we chose propane because it can be separated from the natural process with minimal energy and it will be compatible with the existing infrastructure for easy use” added Dr Jones.

The level of propane that the scientists produced is currently one thousand times less than what would be needed to turn it into a commercial product, so they are now working on refining their newly designed synthetic process. 

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  • Bacteria (Credit: Cesar Harada Source: Flickr)

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Media contact

Bex Caygill

Tel: +44 (0)20 3108 3846

Email: r.caygill [at] ucl.ac.uk