This study provides an attempt to use the extracellular metabolites of a dye-decolorizing strain, Escherichia coli strain NO3, as a biostimulator to entice E. coli strain NO3 into a beneficial mode of metabolism for an economically feasible decolorization. Addition of supernatants containing metabolites from growth and decolorization cultures triggered an enhancement of decolorization rates. Although extracellular metabolites play a crucial role for stimulating decolorization, they still cannot enable decolorization alone without involvement of biodecolorizers (E. coli strain NO3). Substantial decreases in oxidation-reduction potential to negative levels were observed during anaerobic decolorization in the presence of the metabolites. Results of repeated batch cultures also showed that serial acclimation of E coli strain NO3 significantly increased decolorization capability. Supplements of metabolites seem to derepress glucose inhibition on decolorization by E coli strain NO3. The metabolites produced from higher dye-concentration decolorization led to more enhancement of the bacterial decolorization. (C) 2003 Elsevier Ltd. All rights reserved.