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Bacterial Batteries Yield Sweet Success
By Nancy Touchette

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.

Scanning electron micrograph of Rhodoferax ferrireducens attached to a graphite electrode.

“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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Chaudhuri, S.K. and Lovley, D.R. Electricity generation by direct oxidation of glucose in mediatorless microbial fuel cell. Nature Biotechnology, published online September 7, 2003).

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