Effect of electrode spacing on electron transfer and conductivity of Geobacter sulfurreducens biofilms.

To understand electron transport in electrochemically active biofilms, it is necessary to elucidate the heterogeneous electron transport across the biofilm/electrode interface and in the interior of G. sulfurreducens biofilms bridging gaps of varying widths. The conductivity of Geobacter sulfurreducens biofilm bridging nonconductive gaps with widths of 5µm, 10µm, 20µm and 50µm is investigated. Results of electrochemical gating measurement show that biofilm conductivity peaks at the potential of -0.35V vs. Ag/AgCl. The biofilm conductivity increases with gap width (10.4±0.2µScm in 5µm gap, 13.3±0.2µScm in 10µm gap, 16.7±1.4µScm in 20µm gap and 41.8±2.02µScm in 50µm gap). These results revealed that electron transfer in G. sulfurreducens biofilm is a redox-driven. In addition, higher biofilm conductivities and lower charge transfer resistances are observed in all gaps under a turnover condition than in those under a non-turnover condition. Our results offer insights into the spatial heterogeneity of biofilm structure and extracellular electron transfer in electrochemically active biofilms.