The microbial communities associated with electrodes in closed and open circuit microbial fuel cells (MFCs) fed with glucose were analyzed by 16s rRNA approach and compared. The comparison revealed that bacteria affiliated with the Aeromonas sp. within the Gamaproteobacteria constituted the major population in the closed circuit MFC(harvesting electricity) and considered to play important roles in current generation. We, therefore attempted to isolated the dominant bacteria from the anode biofilm, succesfully isolated a Fe (III)-reducing bacterium phylogenetically related to Aeromonas sp. and designated as strain ISO2-3. The isolated strain ISO2-3 could grow and concomitantly produce current (max. 0.24 A/m(2)) via oxidation of glucose or hydrogen with an electrode serving as the sole electron acceptor. The strain could ferment glucose, but generate less electrical current. Cyclic voltammetry supported the strain ISO2-3 was electrically active and likely to transfer electrons to the electrode through membrane-associated compounds (most likely c-type cytochrome). This mechanism requires intimate contact with the anode surface. Scanning electron microscopy revealed that the strain ISO2-3 develeoped multilayer biofilms on anode surface and also produced anchor-like filamentous appendages, (most likely pili) that may promote long-range electron transport across the thick biofilm. Biotechnol. Bioeng. 2009; 104: 901-910. (C) 2009 Wiley Periodicals, Inc.