Stimulation of bacterial decolorization of an azo dye by extracellular metabolites from Escherichia coli strain NO3.

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.