Aims: Isolation, identification and characterization of a new exoelectrogenic bacterium from a microbial fuel cell (MFC). Methods and Results: Exoelectrogenic bacterial strain SX-1 was isolated from a mediator-less MFC by conventional plating techniques with ferric citrate as electron acceptor under anaerobic condition. Phylogenetic analysis of the 16S rDNA sequence revealed that it was related to the members of Citrobacter genus with Citrobacter sp. sdy-48 being the most closely related species. The bacterial strain SX-1 produced electricity from citrate, acetate, glucose, sucrose, glycerol and lactose in MFCs with the highest current density of 205 mA m(-2) generated from citrate. Cyclic voltammetry analysis indicated that membrane-associated proteins may play an important role in facilitating the electrons transferring from bacteria to electrode. Conclusions: This is the first study that demonstrates that Citrobacter species can transfer electrons to extracellular electron acceptors. Citrobacter strain SX-1 is capable of generating electricity from a wide range of substrates in MFCs. Significance and Impact of the Study: This finding increases the known diversity of power generating exoelectrogens and provided a new strain to explore the mechanisms of extracellular electron transfer from bacteria to electrode. The wide range of substrate utilization by SX-1 increases the application potential of MFCs in renewable energy generation and waste treatment.