For more than a decade, scientists have known that strange bacteria living in aquatic mud can conduct electricity along distances thousands of times longer than a single bacterial cell. Such long-range electrical conduction should be extraordinarily difficult for a living organism, and how they accomplish the feat has remained a biological mystery.
Now, researchers say they have found the wiring. Inside so-called cable bacteria, scientists have discovered an elaborate network of nickel-rich nanoribbons arranged into what amounts to a naturally grown electrical cable.
The structure is unlike the conventional machinery biology normally uses to move electrons and may represent the first known example of a metal-organic framework produced by a living organism.
What surprised lead study author Dr. Filip Meysman, a professor at the University of Antwerp in Belgium, most was not how alien the structure looked, but how familiar it was.
“It had a very familiar feeling: a braided wire consisting of thin individual wires surrounded by a protective shell layer,” Meysman told The Debrief. “This is very similar to the power cords that we use to charge our smartphones, only the cable bacterial version is 20,000 times smaller in size. Evolution came up with this design 600 million years earlier than electrical engineers.”
Meysman’s comparison is not simply rhetorical. Molecular-clock estimates suggest the cable bacteria lineage may have diverged roughly 560 million years ago, although when their unusual electrical capabilities evolved is still unknown.
Published in Nature Communications, the findings could eventually provide researchers with a biological blueprint for creating flexible, biodegradable electronics that organisms effectively manufacture themselves.
Cable bacteria first attracted scientific attention because of their outstanding ability to move electrons over centimeter-scale distances. The multicellular organisms live in sediments where different layers offer different chemical resources. Cells buried deeper can harvest electrons from sulfide, while cells closer to oxygen-rich water dispose of them.
The result is an organism that successfully separates parts of its metabolism across space, with electrical current passing along the filament connecting them.
Scientists eventually identified dozens of parallel fibers running through the bacteria’s outer layers as the likely electrical pathways. Measurements later showed conductivity reaching levels unusual for any biological material and, in some experiments, comparable to materials used in electronic inks. The new study notes previously reported conductivity values reaching up to 500 siemens per centimeter.
But knowing where the current traveled was not the same as knowing how it traveled.
Most biological electron conduction relies on proteins containing metal-bearing cofactors, commonly iron-containing structures such as hemes or iron-sulfur clusters. Electrons typically move between those sites in a sequence of molecular transfers often described as “hopping.”
Previous research showed that cable bacteria did not fit neatly into that model. Their conducting fibers were associated with sulfur-bound nickel rather than the usual iron cofactors. At the same time, theoretical work suggested electron movement was too fast to be explained by conventional non-adiabatic hopping alone.
The mystery deepened in 2024, when some of the same researchers examined cable bacteria at temperatures approaching that of liquid helium and found that their electrical behavior matched an unusually efficient multistep hopping mechanism. But even then, the extraordinary conductivity challenged standard models of electrons simply hopping between isolated molecular sites.
The new structural work may help explain why.
Rather than a series of small, separated metal cofactors, the researchers have now found an extended nickel-organic structure running through the conductive fibers.
Using electron microscopy, X-ray fluorescence, Raman spectroscopy, electron paramagnetic resonance, X-ray absorption spectroscopy, and computer modeling, the team found that each conductive fiber contains roughly 11 extraordinarily thin nanoribbons, about 1.4 nanometers across.
Those ribbons pass through the center of the fiber and are built from repeating nickel bis-dithiolene complexes, which the researchers call NiBiD. Nickel atoms are linked through sulfur-containing organic molecules, creating planar units that appear to stack into an extended, highly ordered electrical pathway.
That arrangement may explain the extraordinary conductivity. Rather than electrons simply jumping between isolated metal centers, the stacked structure creates extensive electronic interaction and delocalization, allowing charge to spread across overlapping molecular networks. In that sense, the bacterial wire begins to resemble an organic electronic material more than a conventional biological electron-transfer chain.
The arrangement also appears mechanically well-suited to the bacteria’s lifestyle.
Cable bacteria move through sediment and can bend sharply while maintaining electrical contact between cells. A single rigid conducting strand could be vulnerable to damage. Multiple intertwined nanoribbons, however, offer something closer to braided copper wire: strength, flexibility, and redundancy at the same time.
The discovery also appears to broaden scientists’ understanding of what biology can manufacture.
Metal-organic frameworks, or MOFs, are structures in which organic molecules link together metal centers into larger networks. Chemists have spent years designing them for uses ranging from gas storage and chemical separation to catalysis and electronics.
Until now, the researchers say, no one had observed a metal-organic framework configuration naturally constructed inside a living organism.
Cable bacteria appear to have arrived at the idea on their own, and this natural version appears to conduct electricity exceptionally well.
Previous electrical conductivity measurements of cable bacteria used the entire cross-section of their conductive fibers. But the new structural work indicates that the current is concentrated within a much smaller network of nanoribbons.
Recalculating conductivity based on the estimated dimensions of those conducting channels, the researchers found that an individual nanoribbon could have a conductivity of roughly 150 to 15,000 siemens per centimeter.
That range, the researchers say, ranks among the highest reported for any metal-organic structure. The upper figure remains an estimate, however, instead of a direct measurement of a single nanoribbon.
“We need to be able to isolate the individual nanoribbons from the cable bacteria and connect them electrically with electrodes,” Dr. Meysman explained. “This would provide the direct proof of the high conductivity. We are currently working on such nanoscale electrical measurements.”
Doing so would let researchers determine whether the extraordinary conductivity predicted for an individual nanoribbon holds up experimentally.
If it does, the technological implications could extend well beyond understanding an unusual microbe.
Researchers have long been interested in bio-based electronics because living systems can manufacture sophisticated materials through self-assembly while operating under relatively mild conditions. Biological materials can also be flexible and potentially biodegradable.
Their weakness has usually been electrical performance. Cable bacteria suggest nature may have found a way around that tradeoff.
Scientists still do not know exactly how cable bacteria biosynthesize the nickel-organic framework, and parts of the nanoribbon architecture remain unresolved.
But evolution has already solved one problem materials scientists would like to reproduce: how to build a highly conductive, flexible electrical pathway largely from organic components under biological conditions.
Dr. Meysman says one especially promising possibility is flexible printed electronics, where conductive inks are deposited onto surfaces to create circuits, sensors, and other electronic components.
“The material produced by the bacteria provides a flexible and conductive material, and so flexible printed electronics—conductive inks—emerges as a promising application domain,” Dr. Meysman said.
“The challenge is to demonstrate that the biomaterial can be made in a cost-effective fashion,” Meysman added, “and that it has the same—or even better—properties than the electronic ink materials currently in use.”
Ultimately, for hundreds of millions of years, bacteria buried in mud may have been growing microscopic power cables.
Scientists are only now beginning to understand how they work.
The study, “Highly efficient long-range conduction through a biosynthetic nickel-organic framework,” appeared in Nature Communications.
Tim McMillan is a retired law enforcement executive, investigative reporter and co-founder of The Debrief. His writing typically focuses on defense, national security, the Intelligence Community and topics related to psychology. You can follow Tim on Twitter: @LtTimMcMillan. Tim can be reached by email: tim@thedebrief.org or through encrypted email: LtTimMcMillan@protonmail.com