The electrochemically-active biocathode could be enriched in a two-chamber MFC using graphite felt (Rabaey et al., 2008), granular graphite (Chen et al., 2008), or a carbon fiber brush with graphite granules (Zhang et al., 2012b) as the cathode. Alternatively, a cathode was polarized at a potential lower than 242 mV/SHE to enrich a cathode biofilm in a two-chamber MFC (Liang et al., 2009). It was expected that AZD1480 the cathode redox potential of a two-chamber MFC becomes low enough for electrochemically-active microbes to grow when the cathode was connected to an actively metabolizing bioanode through a suitable external resistance. It is assumed that the increase in electrochemical activities during the enrichment process is the result of the growth of electrochemically-active microorganisms on the electrode. It has been reported that the anode biofilm could be used as an aerobic (Cheng et al., 2012b) or denitrifying biocathode (Cheng et al., 2012a). It is not known if the same organisms catalyze anode reactions, oxidizing electron donors to transfer electrons to the electrode with the cathode reaction consuming electrons available from the electrode to reduce oxygen or nitrate.