Geobacter in 1987, Derek Lovley

Geobacter

In 1987, Derek Lovley was searching the "muddy bottom of the Potomac River just downstream from Washington, D.C., in search of the microscopic creature he believed was interacting with subsurface iron oxide to make phosphorous" (Davis). What he ended up discovering was Geobacter metallireducers, designated GS-15 ("About Geobacter"). This micro-organism has been found to capable of doing some pretty amazing stuff. It may be used to remediate contaminated soil and power batteries, for a variety of useful applications. Geobacter is a reddish-colored micro-organism and are of particular interest due to "their electron transfer capabilities, impact on the natural environment and their application to the bioremediation of contaminated environment and harvesting electricity from waste organic matter" ("About Geobacter").

Geobacter can actually eat groundwater and soil contaminants. Materials dangerous to the environment, such as benzene and MBTE, a gasoline additive, can all be consumed by the handy microbes, even in an environment that's oxygen-free. They're at work cleaning Boston Harbor and have been found to live in dentists' spit sinks. Although they can't decontaminate radioactive material, they do "flourish in uranium-contaminated sites, converting soluble radioactive material to one that's insoluble in groundwater, so it's easier to isolate for cleanup" (Davis).

Davis notes, in addition to their ability to act as a microbial remediation team, Geobacter actually exhales electricity when they breathe in iron oxide, through the 20 to 30 hair-like structures, on the micro-organism, each just 3 to 5 nanometers in diameter, called pili, lined up along one side of the organism. This process finds the bacteria creating webs of electrical wiring, linking each of the bacteria into a web-like electrical circuit. Through this formation, Geobacter is able to rid their bodies of the electrons that were generated during their metabolism process. In nature, this web transports these excess electrons to a distant 'electron dump', making the earth act like a gigantic circuit, for the microbes ("Bacteria")

There are a variety of practical applications that could find this discovery quite useful. The electronics industry could utilize Geobacter Microbial Fuel Cells (MFC) in place of manufacturing nanowires, which come from expensive metals and silica. Geobacter fuel cells could be placed in medical devices that are implanted in a patient, with the organisms feeding off the patient's own blood sugar to power the device, meaning the batteries would never need to be replaced (Davis). Dr. Leonard Tender, at the Naval Research Laboratory, has put this research into use in his Benthic Unattended Generator (BUG). This Geobacter MFC is being utilized to power remote instruments and sensors deployed in marine environments (Greer).

The use of bacteria to generate power is not a new idea. Nearly a century ago, an English botany professor discovered the phenomenon. In fact, Geobacter batteries are similar to bacterial batteries created by scientists, where sugar-eating microbes from the ocean are used to produce electricity from their metabolic process ("Green Energy"). However, in the past, MFCs didn't generate enough power to attract the interest of serious applications. Thanks to technological advancements though, commercial applications for MFCs are likely just around the corner (Greer).

The premise of a Geobacter MFC is similar to a traditional battery. There are two chambers, one which contains an anode and the other which contains a cathode. Geobacter, and their ability to live in an anaerobic environment, are located in the anode chamber. There, they consume and oxidize organic wastes. This process then generates electrons and protons, as their natural metabolic byproduct. These electrons and protons are attracted to oxygen in the cathode chamber and move towards the chamber via two distinct paths. A selective membrane separating the two chambers allows the protons to pass through to the cathode. The negatively charged electrons, on the other hand, are transferred to the anode and travel via external circuit to the cathode, where they combine with the oxygen and the protons to form water. 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).