Cable bacteria conduct electricity through nickel protein wires spanning centimeters

Cable bacteria are among the most electrically unusual organisms on Earth. Filaments of these multicellular microbes stretch up to several centimeters through marine and freshwater sediments, shuttling electrons from sulfide-rich depths up to oxygen at the surface. A study published in Nature Communications has now identified the molecular structure responsible: a set of nickel-containing protein fibers that act as biological wires, conducting electricity with a efficiency that rivals some synthetic materials.

Nickel ions in periplasmic fibers carry current across centimeters

For years, the conductivity of cable bacteria was well-documented but poorly explained. Researchers had confirmed that individual, living filaments maintain a gradient in electrochemical potential from one end to the other, as direct measurements of electron transport in living cable bacteria had shown the gradient collapses the moment oxygen is removed or the filament is cut. What remained elusive was the actual molecular architecture enabling that current.

The Nature Communications team used a combination of spectroscopic and microscopic techniques to zero in on the periplasmic space of the bacteria, the region between the inner and outer cell membranes. There they found a repeated array of fiber-like proteins, each coordinating a nickel ion at its core. Nickel, rather than the iron-sulfur clusters or copper centers common in other biological electron-transfer systems, appears to be the key electroactive atom. The fibers run continuously along the full length of the multicellular filament, forming an unbroken conductive track that can span centimeters, thousands of times the width of a single bacterial cell.

What efficient biological conduction means for sediment chemistry

The practical consequences of this wiring extend well beyond microbiology. Cable bacteria reshape the chemistry of entire sediment columns. By coupling sulfide oxidation at depth to oxygen reduction at the surface, they accelerate sulfur cycling, alter pH profiles across several centimeters of sediment, and suppress the buildup of toxic hydrogen sulfide. Research has shown that cable bacteria can curb methane emissions and aid in breaking down sulfides from oil-eating microbes, making them potential agents for environmental remediation in rice paddies, coastal sediments, and oil-contaminated sites.

Understanding that nickel-protein wires are the mechanism behind this conductivity matters because it opens a design target. If the fibers can be isolated, stabilized outside living cells, or reproduced through synthetic biology, the same long-range electron transport could be harnessed in sensors, fuel cells, or bioremediation systems where moving charge through a biological matrix is desirable. Researchers studying cable bacteria interactions with carbon electrodes in bioelectrochemical systems have already demonstrated that living filaments migrate toward and interface with solid electrodes, hinting at near-term applications in biosensing and bioelectronics.

How the team isolated and characterized the fiber network

Identifying the fibers required stripping away the cell membrane and cytoplasmic contents to leave behind the periplasmic scaffold, then analyzing what remained. Spectroscopy confirmed the nickel coordination environment and showed the metal centers are arranged in a way that allows electron delocalization along the fiber axis. Conductivity measurements on isolated fiber bundles returned values in the range of electronic semiconductors, substantially higher than the proton-mediated or ion-channel mechanisms that power most microbial electrochemistry.

Comparison with other cable bacteria strains, both marine and freshwater, found the same nickel-fiber architecture across phylogenetically distinct lineages, suggesting the system is conserved and ancient rather than a recent evolutionary novelty. The consistency across strains also argues that the fibers, not some parallel pathway, are the dominant route for long-range electron flow.

Open questions about protonic conductivity and fiber diversity

The nickel-protein finding does not close the file on cable bacteria conduction. As studies of the molecular pathway of cable bacteria's conductive network have noted, the precise routing of electrons through the multicellular filament, including how charge crosses the junctions between individual cells, remains incompletely mapped. The Nature Communications paper focuses on the fiber structure itself but stops short of a full circuit diagram.

A separate and intriguing complication emerged from later work showing that hydrated cable bacteria also exhibit protonic conductivity over long distances. Whether proton transport and electron transport operate through the same fiber network or through parallel channels, and whether both are needed for the organism's metabolism, are open questions. The evolutionary pressure that drove cable bacteria to invest in such elaborate wiring, rather than simpler short-range electron shuttles used by other electroactive microbes, is also not yet understood.

Toward bio-inspired nanowires and sediment engineering

The immediate next step is atomic-level structural characterization of the nickel-protein fibers, ideally through cryo-electron microscopy at sufficient resolution to place each nickel ion within the protein fold. That structure would reveal whether the conductivity arises from a metal-to-metal hopping mechanism, from a delocalized band across the protein backbone, or from some hybrid pathway. Each answer points to a different strategy for engineering analogous materials.

Longer term, the discovery raises the possibility of deploying cable bacteria deliberately in sediment management, using their natural wiring to accelerate sulfur removal in eutrophic coastal zones or to reduce methane flux from agricultural wetlands. The nickel-fiber architecture, once fully characterized, could also inform the design of protein-based nanowires for soft electronics, where rigid metal conductors are impractical. Biological systems have already solved the problem of conducting electrons across centimeter scales in a flexible, self-assembling filament. The engineering question is how closely synthetic systems can replicate that solution.