A graphite electrode and a stainless steel electrode immersed in exactly the same medium and polarised at the same potential were colonised. by different microbial biofilms. This difference in electroactive microbial population leads stainless steel and graphite to become a microbial cathode and a microbial anode respectively. The results demonstrated that the electrode material can drive the electrocatalytic property of the biofilm opening perspectives for designing single medium MFC. This new discovery led to of the first demonstration of a "single medium MFC." Such a single medium MFC designed with a graphite anode connected to a stainless steel cathode, both buried in marine sediments, produced 280 mA m(-2) at a voltage of 0.3 V for more than 2 weeks. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.