Genome scale gene expression studies and electrochemical analysis indicate that cells in direct contact with the anode in a MFC interact through c-type cytochromes on the outer cell surfaces. Interestingly G. sulfurreducens biofilms can form biofilms greater than 50 μm thick. All the cells in the thick biofilm are metabolically active and contribute to current production . Gene expression studies have suggested that the production of microbial nanowires is important for long-range electron transfer through the G. sulfurreducens biofilms (Figure 3) . Modeling studies have also predicted that high current production by a thick anode associated biofilm is only feasible if the bacterial biofilm is conductive . The production of a conductive biofilm is highly unusual as most biofilms act as insulators . A major breakthrough in the field would be the measurement and determination of the conductivity, and the components responsible of conductivity, of a bacterial biofilm in a MFC.