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 °C to + 50 °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 ~ 0.1 cm2/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.
Highlights
Filamentous cable bacteria exhibit long-range electron transport over centimetre-scale distances, which takes place in a parallel fibre structure with high electrical conductivity
We report the intrinsic electrical properties of dry cable bacterium filaments with different characterization techniques
We found a single semicircle in the complex plane, indicating that cable bacteria can be considered as biological electrical wires with ohmic contacts
Summary
Filamentous cable bacteria exhibit long-range electron transport over centimetre-scale distances, which takes place in a parallel fibre structure with high electrical conductivity. Direct electrode measurements reveal that individual cable bacterium filaments can guide electrical currents over distances up to 1 cm under an externally applied potential[5]. This length scale of conduction for a single organism surpasses greatly that of other known current-producing bacteria, such as Geobacter sulfurreducens and Shewanella oneidensis MR-1. Microscopy investigations reveal that all cells within a cable bacterium filament share a common space within the cell envelope, and that a network of parallel fibres run within this periplasmic space along the whole filament[8,9]. We employed the same techniques in a cryostat set-up to study the conductivity and mobility as a function of temperature
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