Microbial electrolysis cells (MEC), inspired from microbial fuel cells (MFC), are mainly used to produce hydrogen from organic matter oxidation through the input of a small amount of electrical energy. Hydrogen production occurs by electrochemical reduction of protons at the cathode associated with a bioanode on which an electroactive biofilm oxidizes organic matter. To date, only few studies have focused on electroactive microorganisms in mixed cultures bioanodes submitted to a controlled applied potential. The aim of this study is the selection and the identification of electroactive organisms on mixed culture bioanodes with regards to electron-transfer performance of the electroactive biofilm. As experimental design, a three-electrode system was used in which the graphite working electrode potential was fixed with a potentiostat (Biologic VSP) according to a Ag/AgCl reference electrode. The current produced between the working electrode and an auxiliary electrode was monitored. Three different sources of inoculum were tested: sediments from a salt lake beach, from a salt-producing platform and soil samples. A voltage of 0.2 V vs Ag/AgCl was applied to the anode with acetate as carbon source, in natural or synthetic seawater, at pH 6 or 7. The final biofilm was collected and microbial diversity was analyzed by PCR-SSCP and Pyrosequencing. While current densities obtained ranged from 8.32 à 16.9 A / m², a strong selection pressure occurred in the reactor: Interestingly, only one or two species were selected as main dominant in the anode biofilms. The most abundant species found in electroactive biofilms were genetically close and were Geobacter sp. in soil-inoculated reactor, and Desulfuromonas acetoxidans and Geoalkalibacter subterraneus in sediments. Although Geobacter sp. and Desulfuromonas sp. have been widely described in the literature, Geoalkalibacter subterraneus is described for the first time as an electricigen organism in this study.