The anaerobic decolorization of metal-complex dye Naphthol Green B (NGB) by a metal-reducing bacterium, Shewanella oneidensis MR-1, was investigated. S. oneidensis MR-1 showed a high capacity for decolorizing NGB even at a concentration of up to 1000 mg/L under anaerobic conditions. Maximum decolorization efficiency was appeared at pH 8.0 and 40 degrees C. Addition of iron oxide caused no inhibition to the NGB decolorization, while the presence of ferric citrate, nitrite, or nitrate almost completely terminated the decolorization. Biosynthesis of nanomaterials was observed coupled with the degradation of NGB when thiosulfate was added. The Mtr respiratory pathway was found to be responsible for the decolorization of NGB by S. oneidensis, in which extracellular electron shuttle also plays a positive role in promoting the decolorization. (C) 2012 Elsevier Ltd. All rights reserved.