A new facultative anaerobic exoelectrogenic strain LZ-1, belonging to Citrobacter freundii, has been isolated. This strain can produce current densities of 843.9 and 865.6 mu A cm(-2) using citrate or acetate as carbon source in a three-electrode configuration. The electricity generation performance was also analyzed in a dual-chamber MFC system, reaching a maximum power density of 1233 mW m(-2). In addition to acetate and citrate, other carbon sources such as pyruvate, formate, acetate, citrate and fumarate could also be utilized to produce current by strain LZ-1. Data supports the presence of electroacfive c-type cytochromes in C. freundii sp. when grown on ITO electrodes, by linking spectroscopy and electrochemistry in situ. Since facultative strains possess many desirable properties compared to anaerobic strains, strain LZ-1 represents a promising exoelectrogenic species in engineering of biological catalysts for microbial electrochemistry.