Extraordinary Wires Made by Ordinary Bacteria
Giving new meaning to the phrase “lightning bug,” scientists have come up with a way to get bacteria to produce infinitesimal wires capable of conducting useful amounts of electricity.
The work, by researchers at the University of Massachusetts, relies on a garden-variety bacteria to produce the wires from naturally occurring proteins. Someday, such wires might be useful anywhere that really small electronics are wanted. And unlike many electronic components today, these bacterial wires can be produced using nontoxic, sustainable materials.
The researchers used a bacteria called Geobacter that was first discovered in 1987 in the Potomac River, not far downstream from Washington, D.C. Geobacter can live on a wide range of nutrient sources and has displayed a talent for cleaning up petroleum and radioactive-metal contamination. Intriguingly, the bacteria gets energy from iron oxide in the soil, handing off electrons in the process through tiny filaments that function like electrical wires.
It is easy for scientists to grow Geobacter, but in nature, the bacteria’s tiny hairs can’t carry much current. So the University of Massachusetts scientists carried out a relatively simple genetic manipulation that caused the bacteria to grow filaments containing tryptophan, an important amino acid that is often (wrongly) blamed for drowsiness after a traditionally turkey-heavy Thanksgiving meal. Tryptophan turns out to be quite good at moving electrons in a nanoscale setting—that is, when the materials involved are just billionths of a meter in size.
That modest genetic intervention was wildly successful, boosting electrical conductivity by 2,000 times while shrinking the filaments to about half the thickness of the original. How narrow are they? They’re about 60,000 times thinner than a human hair—yet extremely durable. Derek Lovley, one of the University of Massachusetts scientists and a co-author of a new paper describing their findings, says that the filaments can then be knit together into longer strands by embedding them in resins or plastics. The required lengths tend to be extremely short, in keeping with the insatiable demand for extreme miniaturization.
These microbial nanowires could have a variety of applications in ever-smaller devices. For instance, Dr. Lovley says, Geobacter filament conductivity varies enormously depending on the acidity of the environment. That suggests that the filaments could be used in medical sensors—perhaps in the human body, where their sensitivity to pH changes could provide early warnings.
Dr. Lovley says that the bacterial filaments also have electrical properties that would enable them to function as transistors (a basic element in microchips) and thus in all sorts of computer devices. He adds that the biowires could even function as capacitors, which take on the role of temporary batteries. Efficient bacterial wires “also make it possible to electrically connect cells to electronic devices,” Dr. Lovley says, which could enable “biology and electronics to talk together.” That could open the door to biological computing devices and artificial forms of photosynthesis, he says.
Another potential benefit: the prospect of electronics that could be produced with fewer harmful substances. Dr. Lovley notes that Geobacters can be fed on almost any kind of plant waste. They can even be raised on carbon dioxide and sustainably produced electricity, such as solar power.
Now, Dr. Lovley says, his team is working on customized bacteria optimized for maximum filament conductivity, much as one might try to breed a spider optimized for silk production.
“Synthetic Biological Protein Nanowires with High Conductivity,” Yang Tan, Derek Lovley and co-authors, Small (July 13)