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

• The effect of gap width on biofilm conductivity was investigated. • Higher conductivity was observed for biofilm bridging on larger gaps. • Redox-driven EET was found for biofilms bridging gaps with different width. • Metabolic activity controls biofilm conductance. 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 5 µm, 10 µm, 20 µm and 50 µm is investigated. Results of electrochemical gating measurement show that biofilm conductivity peaks at the potential of −0.35 V vs. Ag/AgCl. The biofilm conductivity increases with gap width (10.4 ± 0.2 µS cm−1 in 5 µm gap, 13.3 ± 0.2 µS cm−1 in 10 µm gap, 16.7 ± 1.4 µS cm−1 in 20 µm gap and 41.8 ± 2.02 µS cm−1 in 50 µm 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. [ABSTRACT FROM AUTHOR]