The electron-donating strains in anode suspension of microbial electrolysis cell (MEC) have not been probed. This work for the first time isolated from the anode suspension in a double-chamber MEC a Fe(III)-reducing strain W7, which is a Gram-negative, short rod, polar flagellum, non-spore-forming bacterium. Physiological-biochemical characterization and 16S rRNA gene sequence analysis suggested that this strain is a typical fermentative bacterium and is designated to the strain Bacteroides sp. W7 (GeneBank accession no. FJ862827). The strain W7 could reduce Fe(III) to form 8.5 mmol L(-1) of Fe(II) in 39 h cultivation. Moreover, this strain can transfer electrons to Fe(III) during its growth by adopting glucose, yeast extract and sodium lactate as carbon source. The presence of this Fe(III)reducing fermentative bacterium suggests the possible contribution of suspended organisms to the efficiency of MEC. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.