In microbial electrochemical cells the anode potential can vary over a wide range, which alters the thermodynamic energy available for bacterial-electrode electron exchange (termed electroactive bacteria). We investigated how anode potential affected the microbial catalytic response of the electroactive biofilm. Microbial biofilms induced to grow on graphite electrodes by application of a fixed applied anode potential in membrane-separated and membrane-less electrochemical cells show differences in electrocatalytic response. Maximum current density is obtained using +0.2 V vs. Ag/AgCl to induce biofilm growth in membrane-less cells, in contrast to a maximum achieved at lower applied potentials in a membrane-separated electrochemical cell configuration. This insight into differences in optimal applied potentials based on cell configuration can play an important role in selection of parameters required for microbial fuel cells and bio-electrochemical systems. (C) 2013 Elsevier B.V. All rights reserved.