Four microbial fuel cells (MFCs) were inoculated with anaerobic sludge and fed four different substrates for over one year. The Coulombic efficiency (CE) and power output varied with different substrates, while the bacterial viability was similar. Acetate-fed-MFC showed the highest CE (72.3%), followed by butyrate (43.0%), propionate (36.0%) and glucose (15.0%). Glucose resulted in the lowest CE because of its fermentable nature implying its consumption by diverse non-electricity-generating bacteria. 16S rDNA sequencing results indicated phylogenetic diversity in the communities of all anode biofilms, and there was no single dominant bacterial species. A relative abundance of beta-Proteobacteria but an absence of gamma-Proteobacteria was observed in all MFCs except for propionate-fed system in which Firmicutes dominating. The glucose-fed-MFC showed the widest community diversity, resulting in the rapid generation of current without lag time when different substrates were suddenly fed. Geobacter-like species with the most representative Geobacter sulfurreducens PCA(T) were integral members of the bacterial community in all MFCs except for the propionate-fed system. (C) 2009 Published by Elsevier Ltd.