Intrinsic electrical properties of cable bacteria reveal an Arrhenius temperature dependence

Abstract

Filamentous cable bacteria exhibit long-range electron transport over centimetre-scale distances, which takes place in a parallel fibre structure with high electrical conductivity. Still, the underlying electron transport mechanism remains undisclosed. Here we determine the intrinsic electrical properties of the conductive fibres in cable bacteria from a material science perspective. Impedance spectroscopy provides an equivalent electrical circuit model, which demonstrates that dry cable bacteria filaments function as resistive biological wires. Temperature-dependent electrical characterization reveals that the conductivity can be described with an Arrhenius-type relation over a broad temperature range (- 195 degrees C to+50 degrees C), demonstrating that charge transport is thermally activated with a low activation energy of 40-50 meV. Furthermore, when cable bacterium filaments are utilized as the channel in a field-effect transistor, they show n-type transport suggesting that electrons are the charge carriers. Electron mobility values are similar to 0.1 cm(2)/Vs at room temperature and display a similar Arrhenius temperature dependence as conductivity. Overall, our results demonstrate that the intrinsic electrical properties of the conductive fibres in cable bacteria are comparable to synthetic organic semiconductor materials, and so they offer promising perspectives for both fundamental studies of biological electron transport as well as applications in microbial electrochemical technologies and bioelectronics.