Temperature-Dependent\nCharacterization of Long-Range\nConduction in Conductive Protein Fibers of Cable Bacteria

Multicellular cable bacteria display an exceptional form\nof biological\nconduction, channeling electric currents across centimeter distances\nthrough a regular network of protein fibers embedded in the cell envelope.\nThe fiber conductivity is among the highest recorded for biomaterials,\nbut the underlying mechanism of electron transport remains elusive.\nHere, we performed detailed characterization of the conductance from\nroom temperature down to liquid helium temperature to attain insight\ninto the mechanism of long-range conduction. A consistent behavior\nis seen within and across individual filaments. The conductance near\nroom temperature reveals thermally activated behavior, yet with a\nlow activation energy. At cryogenic temperatures, the conductance\nat moderate electric fields becomes virtually independent of temperature,\nsuggesting that quantum vibrations couple to the charge transport\nthrough nuclear tunneling. Our data support an incoherent multistep\nhopping model within parallel conduction channels with a low activation\nenergy and high transfer efficiency between hopping sites. This model\nexplains the capacity of cable bacteria to transport electrons across\ncentimeter-scale distances, thus illustrating how electric currents\ncan be guided through extremely long supramolecular protein structures.