- Bacteria Grow Organic Local-Area Networks
- Researchers believe that recently discovered microbial "electrical hairs" work like nanoscale local-area networks, allowing bacteria to communicate shared threats, collective capabilities and other information that helps the colony distribute resources and survive.The human body has long been known to perform internal communications among nerve cells with electro-chemical signals, but now bacteria have been shown to set up their own external communication links among widely separated cells using organic nanowires.
Bacteria are independent cells that live together in colonies."For a long time we knew that bacteria could move electrons through their cells, but what we know now is that they can build wires—the idea being that they grow these hairlike appendages out of their cell bodies," said Professor Moh El-Naggar at the University of Southern California (Los Angeles). "They build this wire out of their cell body all the way to the electrons they are breathing, which could be the electrode of a microbial fuel cell. You essentially use that wire to transport electrons just like you would use a breathing tube to breathe oxygen."
Respiration is the hallmark of all living systems. Human respiration is usually thought of as acquiring oxygen and getting rid of carbon dioxide, but electronically breathing could be viewed as ridding us of excess electrons. Likewise, bacteria appear to use these until now mostly ignored nanowires to rid themselves of excess electrical charge. There is also evidence that the lines are used for communications among widely dispersed cells, such as in planar biofilms, which can benefit from providing conduits to shed the excess electrical charge produced by respiration.
For years, scientists had noticed the hairlike connections, and noted that they seemed to sprout between cells in times of shortages, perhaps permitting the sharing of resources. Now researchers for the first time actually measured the resistance of the nanowires and found them to be semiconducting. The researchers speculate that in nature, these nanowires are used to normalize the metabolic status a biofilm, whereas they propose repurposing them to form self-repairing structures in organic circuitry like the microbial fuel cells under development at USC.
In times of stress, here immobilized in a biofilm, bacteria grow nanowire-like appendages between cells.The researchers had become interested in measuring the resistance of nanowires when they noticed that electrical reduction of metals—rusting—appeared to be occurring around the nanowires, indicating that current was flowing. Since reduction requires the transfer of electrical charge to a metal, the researchers suspected that the nanowires were carrying an electrical current.
To measure the conductivity of these nanowires, the researchers grew cultures of Shewanella oneidensis, which was discovered by Professor Kenneth Nealson at USC. By manipulating the environment of the culture, the researchers were able to induce them to grow interconnecting nanowires. Like human hairs, the nanowires growing out of bacteria consist mostly of protein, but when their resistance was measured, their conductivity was found to be semiconducting like microchips.
Funding was provided by the Air Force Office of Scientific Research, the U.S. Department of Energy, the Legler-Benbough Foundation, the J. Craig Venter Institute, the Canadian Natural Science and Engineering Research Council, and the Canada Foundation for Innovation and Surface Science Western.