Influence of inoculum and anode surface properties on the selection of Geobacter-dominated biofilms

• Dry soil MFC had longest start-up time (28 days) and poor current output.
• COO− anodes had longest start-up times (6.3 days) but highest power output (118 mW m−2).
• All biofilms selected were dominated by Geobacter sp.
• Geobacter sp. is widespread in soils, even those frequently exposed to oxygen.
• Geobacter is very much better at growing in MFC conditions than any other bacteria.

This study evaluated the impact of inoculum source and anode surface modification (carboxylate –COO− and sulfonamide –SO2NH2 groups) on the microbial composition of anode-respiring biofilms. These two factors have not previously been considered in detail. Three different inoculum sources were investigated, a dry aerobic soil, brackish estuarine mud and freshwater sediment. The biofilms were selected using a poised anode (−0.36 V vs Ag/AgCl) and acetate as the electron donor in a three-electrode configuration microbial fuel cell (MFC). Population profiling and cloning showed that all biofilms selected were dominated by Geobacter sp., although their electrochemical properties varied depending on the source inoculum and electrode surface modification. These findings suggest that Geobacter sp. are widespread in soils, even those that do not provide a continuously anaerobic environment, and are better at growing in the MFC conditions than other bacteria.