The stream of electrons passing through the external circuit generates a flow of electricity (Greer). But, it's Geobacter's unique abilities that have allowed the reality of useful MFCs to come to fruition.

In the past, other microbes used for MFCs only converted a small percentage of the electrons available in their food into electricity. Geobacter processes electrons differently from other microbes though. Instead of transferring the electron byproducts into oxygen, Geobacter transfers their excess electrons to alternative electron acceptors, which makes them very efficient in transferring this power to the anode of an MFC.

Lovley had deemed this type of organism an "electricigen" and notes that Geobacter often converts 90% of the available electrons in their metabolic process (qtd. Greer).

In addition to this increased efficiency, Geobacter also eliminates the need for electron mediators needed when other microbes are utilized for MFCs. These artificial compounds are used to promote electron transfer between the electrode and the cell, increasing efficiency. The problem with electron mediator compounds are that they're typically unstable, expensive and toxic to humans. MFCs created with other bacteria also were not long-lasting. Other organisms previously used would not retain sufficient electrons to foster their own growth. In contrast, Geobacter conserves a small amount of the electricity it produces for the maintenance and growth of its cells, making these fuel cells basically immortal, as long as they have fuel. In addition to the advancements afforded by Geobacter's unique metabolic process, there is also considerable development being undertaken to redesign MFCs, in order to increased power density. Better design of the fuel cells has already seen an increase of a couple orders of magnitude (Greer).

This redesign process, Greer reports, has also resulted in another exciting discovery. With older configurations of MFCs, only a single layer of microbes coated the anode surface, resulting in a low power density. However, using Geobacter...

The scientists found that the amount of current that the MFC produced was directly correlated with the thickness of the biofilm. Therefore, they have surmised that although some of the piggybacked organisms are a considerable distance from the anode, they are still contributing as much power as their fellow organisms in the first layer. Just as in nature, Geobacter was forming a conductive web amongst themselves, allowing the microbes not in direct contact with the anode to still transfer electrons to it.
In the end, from the muds of the Potomac River has come an exciting discovery. Not only do these amazing microbes have the ability to remediate our world, but can be used for electricity production as well. Although the process of MFCs is not new, the discovery of Geobacter and it's unique process of metabolism, coupled with its ability to create a biological circuit, makes the possibility of MFCs being used in commercial application a reality. Whether used to power computers or medical devices or remote instruments, these self-sustaining, immortal batteries are only at the beginning of what possibilities may lie ahead.

Works Cited

About Geobacter. 2008. Geobacter.org. December 4, 2008 http://www.geobacter.org/.

Bacteria May Be Wiring Up the Soil." Nature. 26 Sept. 2007. Geobacter.org. December 4, 2008 http://www.geobacter.org/press/2007-09-26-nature.pdf.

Davis, R. "Little Geobacter Still Sparks Discoveries After 20 Years." The Greenfield Reorder. 15 June 2007. Geobacter.org. December 4, 2008. http://www.geobacter.org/press/2007-06-15-greenfieldrecorder.pdf.

Green Energy." Time. 30 Aug 2007. Geobacter.org. December 4, 2008. http://www.geobacter.org/press/2007-08-30-time.pdf.

Greer, D. "Harnessing the Power of Microbes." Biocycle. May 2007. Geobacter.org. December 4, 2008. http://www.geobacter.org/press/2007-05-15-biocycle.pdf.