Carbon-based nanomaterials enhance the growth of cable bacteria in brackish sediments

Cable bacteria are long, multicellular bacteria that conduct electrical currents over centimetre distances within sediment to support their metabolism. Recent studies have shown their potential for extracellular electron transport (EET), allowing the possibility to donate electrons to solid electrodes and potentially enabling electrical interactions with other microbes. However, the mechanisms and capabilities of their EET, and their potential to interact electronically with other materials in their environment has not been explored. As sediment can contain conductive minerals, this study aimed to investigate the effect of carbon-based colloidal nanomaterials such as graphene oxide (GO), sulfur-doped graphene oxide (S-GO), and carbon nanotubes on cable bacteria. When S-GO was added to sediment, cable bacteria grew with higher activity, and in higher density at depth, whilst GO had little initial effect but showed a delayed enhancement of cable activity. This is thought to be due the reduction of GO via iron oxidation within the sediment, allowing it to become more conjugated, resulting in more similar conductive properties to S-GO. We speculate that the enhancement of cable bacteria growth is due to the electron shuttling properties of S-GO and similar materials, allowing for more efficient transfer of electrons between cable bacteria and to electron acceptors.