Quantum-assisted electron transport in microbial protein wires across macroscopic distances

Multicellular cable bacteria display an exceptional form of biological conduction, channeling electrical currents across centimeter distances through a regular network of protein fibers embedded in the cell envelope. The fiber conductivity is among the highest recorded for biomaterials, providing a promising outlook for new bio-electronic technologies, but the underlying mechanism of electron transport remains elusive. Here, we use detailed electrical characterization down to cryogenic temperatures, which reveals that long-range conduction in these bacterial protein wires is based on a unique type of quantum-assisted multistep hopping. The conductance near room temperature reveals thermally activated behavior, yet with a low activation energy, suggesting that substantial delocalization across charge carrier sites contributes to high conductivity. At cryogenic temperatures, the conductance becomes virtually independent of temperature, thus indicating that quantum vibrations couple to the charge transport. Our results demonstrate that quantum effects can manifest themselves in biological systems over macroscopic length scales.