The bioconversion of xenobiotics often involves oxidation-reduction reactions and one representative example is the reductive decolorization of azo dyes. The bioreduction of an azo dye as model xenobiotic by a mixed microbial culture (activated sludge) was thus chosen as a model system in the present study. The aim was to investigate the effect of a respiratory inhibitor, namely sodium azide (a cytochrome oxidase inhibitor) on this bioconversion, when carried out by two different activated sludge mixed culture inocula. Different biomass conditioning pretreatments were also studied, i.e., using a mixed culture freshly harvested from the growth bioreactor or after aerobic incubation in the absence of carbon source (starved). The azide inhibition effect was observed to lessen with the increase in starvation time for both mixed cultures. This result points to the existence of an alternative dye bioconversion mechanism, triggered in the starved biomass, in which the involved pathways are not inhibited by azide. For one of the inocula, this alternative mechanism was found to be dependent on the availability of glucose in the bioconversion medium.
