Nanowire-Armed Bacteria Become Living Biological Circuits
Bacteria can grow nanowires that resemble electrically conducting hairs to share energy, take a collective breath and perhaps even communicate, a new experiment reveals.
The Shewanella oneidensis bacteria were seen in action as living biological circuits for the first time by researchers, who tested the ability of the microbes to close a circuit between microscopic electrodes.
When the nanowires, which are made mostly out of proteins (much like our hair), linked up across two electrodes and closed the circuit, they created a flow of measurable current. Cutting the nanowires stopped the current flow.
"This is the first measurement of electron transport along biological nanowires produced by bacteria," said Mohamed El-Naggar, a biophysicist at the University of Southern California in Los Angeles.
Such bacteria breathe or respire by giving up electrons to a metal such as iron. By contrast, human breathing gives up electrons to oxygen, hence our need for oxygen gas.
Bacteria that don't have access to something that can accept the electrons will die. But they can grow nanowires under dire circumstances and connect with other bacteria to form a chain that can transport electrons to distant sources of electron acceptors.
"This would be basically a community response to transfer electrons," El-Naggar said. "It would be a form of cooperative breathing."
El-Naggar and his colleagues took advantage of the Shewanella's natural response to hard times and manipulated their conditions to ensure that they grew many nanowires.
The term "bacterial nanowire" only just emerged in 2006. Fewer than 10 studies on the subject have been published, according to co-author Yuri Gorby of The J. Craig Venter Institute in San Diego, who discovered nanowires in Shewanella.
Researchers first noticed that metals near the bacterial nanowires seemed to gain electrons, or undergo a process called reduction. That triggered the suspicion that such nanowires could carry an electric current.
Knowing how microbial communities thrive could help to promote useful colonies, such as those in bacterial fuel cells to power the future.
Many bacteria appear to use such nanowires for cooperative survival, researchers say. Some scientists have even hypothesized that the nanowires permit the microbes to communicate.
Bacterial colonies already talk through a slower chemical process of signaling molecules. But conducting electrons over the nanowire network could be much faster, said study researcher Kenneth Nealson, Wrigley Professor of Geobiology at USC College, who first discovered Shewanella.
"You want the telegraph, you don't want smoke signals," Nealson said.
The study is detailed in the Oct. 11 issue of the journal Proceedings of the National Academy of Sciences.
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