Microbes Produce Miniature Electrical Wires

Researchers at the University of Massachusetts Amherst have discovered a tiny biological structure that is highly electrically conductive. This breakthrough helps describe how microorganisms can clean up groundwater and produce electricity from renewable resources. It may also have applications in the emerging field of nanotechnology, which develops advanced materials and devices in extremely small dimensions.

Researchers found that a novel microorganism known as Geobacter produces the conductive structures, known as "microbial nanowires." The nanowires are incredibly fine, only 3 to 5 nanometers in width, but quite durable and more than a thousand times long as they are wide.

Geobacter are the subject of intense investigation because they are useful agents in the bioremediation of groundwater contaminated with pollutants such as toxic and radioactive metals or petroleum. They also have the ability to convert human and animal wastes or renewable biomass into electricity. To carry out these processes, Geobacter must transfer electrons outside the cell onto metals or electrodes. This new research provides an explanation of how this can happen.

Previous studies demonstrated that Geobacter produces fine, hair-like structures, known as pili, on just one side of the cell. The team speculated that the pili might be miniature wires extending from the cell that would permit Geobacter to carry out its unique ability to transfer electrons outside the cell onto metals and electrodes. Furthermore, when Geobacter was genetically modified to prevent it from producing pili, Geobacter could no longer transfer electrons.

The conductive pili that Geobacter produces may have a variety of applications for the electronics industry. Ultrafine wires (nanowires) are required for further miniaturization of electronic devices. Manufacturing nanowires from more traditional materials such as metals, silica, or carbon is difficult and expensive. However, it is easy to grow billions of Geobacter cells in the laboratory and harvest the microbial nanowires that they produce. Furthermore, by altering the DNA sequence of the genes that encode for microbial nanowires, it may be possible to produce nanowires with different properties and functions.

Another interesting implication of this research is that it suggests a mechanism for microbes to share energy in a mini-power grid. The nanowire pili of individual Geobacter often intertwine, suggesting a strategy by which Geobacter might share electricity.

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