Researchers have engineered the harmless gut bacteria 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.
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.
In a new study, the team of scientists from Imperial College London
and the University of Turku in Finland used Escherichia coli to
interrupt the biological process that turns fatty acids into cell
membranes. The researchers used enzymes to channel the fatty acids along
a different biological pathway, so that the bacteria made engine-ready
renewable propane instead of cell membranes.
Their ultimate goal is to insert this engineered system into
photosynthetic bacteria, so as to one day directly convert solar energy
into chemical fuel.The results of the study are published in the journal Nature Communications.
Dr Patrik Jones, from the Department of Life Sciences at 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.
Using E. coli as a host organism, the scientists interrupted the
biological process that turns fatty acids into cell membranes. By
stopping this process at an early stage they could remove butyric acid, a
nasty smelling compound that is an essential precursor for propane
production.
To interrupt the process, the researchers discovered a new variant of
an enzyme called thioesterase which specifically targets fatty acids
and releases them from the natural process. They then used a second
bacterial enzyme, called CAR, to convert butyric acid into
butyraldehyde. Finally, they added a recently discovered enzyme called aldehyde-deformylating
oxygenase (ADO), which is known to naturally create hydrocarbons, in
order to form propane.
Previous attempts to use the ADO enzyme have proved disappointing as
scientists have been unable to harness the natural power of the enzyme
to create cleaner fuel. But the scientists at Imperial discovered that
by stimulating ADO with electrons they were able to substantially
enhance the catalytic capability of the enzyme, and ultimately produce
propane.
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. Dr Jones said: "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 5-10 years we will be able to achieve commercially viable
processes that will sustainably fuel our energy demands."
This research was funded by a grant from the European Research Council.
Source: Imperial College London
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