A rapid and simple protocol to prepare a living biocomposite that mimics electroactive biofilms

A living material was formed by self-assembly of bacterial cells (Shewanella oneidensis MR-1 or Pseudomonas fluorescens) with carbon nanotubes in the presence of cytochrome c from a bovine heart with the goal to mimic electroactive biofilms. The role of cytochrome c on self-assembly, cell viability and extracellular electron transfer was studied. Scanning electron microscopy and dynamic light scattering experiments highlighted its role on the self-assembly of bacteria‑carbon nanotube aggregates within only 2h in solution. The deposition of these aggregates on glassy carbon surfaces led to a homogenous composite film in which the bacteria were embedded in a carbon nanotube network. A comparable cell density of 1cellμm^-2 was achieved in the presence or in the absence of cytochrome c, but this protein allowed maintaining a higher bacterial viability. Electrochemical characterization demonstrated the role of cytochrome c on electron transfer reactions, leading to a current density of up to 300μAcm^-2 in the presence of 50mM formate when a porous carbon felt electrode is used as support for the biocomposite.