Forget the Energizer
Bunny. Now it’s time for the Bacterial Battery. Researchers have figured out
a way to generate electricity by feeding bacteria common sugars and other
carbohydrates. The breakthrough could lead to novel strategies for
generating energy and for getting rid of agricultural and industrial waste.
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Scanning electron micrograph of Rhodoferax
ferrireducens attached to a graphite electrode.
Image courtesy Derek R. Lovley/UMASS Amherst.
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“The concept of using microbes to power fuel cells has been around for a
while, but until now it hadn’t amounted to much more than parlor curiosity,”
says Leonard M. Tender of the Naval Research Laboratory’s Center for
Bio/Molecular Science and Engineering in Washington, D.C. “The key here was
to use a microbe that can produce electrons and directly transfer them to
electrodes.”
In the new study, reported in Nature Biotechnology, Swades K.
Chaudhuri and Derek R. Lovley of the University of Massachusetts in Amherst,
grew bacteria on graphite electrodes in a fuel cell. When the bacteria were
fed glucose or other sugars, they generated electrons and transferred them
to the graphite electrodes. The flow of electrons from the bacteria to the
electrode generated electricity that the battery could store.
“This is a small step, but it’s an important step,” says Tender. “The
lessons learned here will go a long way toward improving the way we generate
electricity and how we choose our fuels.”
The researchers made use of a bacterium called Rhodoferax
ferrireducens, which they discovered in sediments collected from Oyster
Bay, Virginia. The researchers were interested in the bacteria because they
thrive in the presence of iron and other metals.
Most organisms can metabolize sugars and other organic matter as fuel in
a process known as respiration. In the process, they generate electrons that
combine with oxygen, when it is present, to produce water. In the absence of
oxygen, Rhodoferax ferrireducens transfers its electrons to iron
and other minerals in the surrounding environment.
“This is a type of respiration that no one has really focused on before,”
says Lovley. “We hit on something new and it had a quick payoff.”
Other researchers, including Lovely, have tried in the past to harvest
the electrons generated by microbial respiration. But the efficiency in
either generating electrons from glucose or intermediate products or in
harvesting the electrons has been inefficient. In the present study the
researchers were able to harvest 85 percent of all the energy produced from
the breakdown of glucose.
Still, the researchers have a way to go before the microbes can be used
as a viable energy source.
“Right now, the process is very slow,” says Lovley. “We can generate
enough electricity to power a Christmas tree bulb or calculator, but not
much more. Until we can speed up the process, it may be more useful as a way
of recharging batteries.”
Lovley and his colleagues are investigating ways to improve the
efficiency and speed of the system. Because the bacteria normally transfer
electrons to iron and other metals, not graphite, they are testing metals as
components of the electrodes in the batteries. They are also trying to
increase the surface area of the electrodes to allow more bacteria to grow.
Ultimately, the system could be used to generate electricity from organic
waste materials. Tender says other types of bacteria may feed on a whole
range of waste materials and that developing such systems could solve two
problems at once: generating energy and removing waste matter from the
environment.
“This opens up a whole new way of looking at our world,” says Tender.
“Microorganisms are very clever and adaptable. Whatever the fuel source is,
there is probably a microbe out there somewhere that will eat it.”
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