Abstract: To address the environmental pollution caused by azo dyes,Shewanella oneidensisMR-1 was selected as the model organism to study its capacity to reduce and decolorize the polyazo dye Direct Black 168 under anaerobic conditions, and to optimize degradation conditions. The results showed that the dye decolorization rate reached 96% when sodium lactate was used as the electron donor, with an incubation temperature of 30 ℃ and an initial inoculum of 5×107CFU/mL. Wild-typeS. oneidensisdecolorized polar polyazo dyes containing sulfonic acid groups via the Mtr pathway, whereas gene knockout strains exhibited inhibited dye degradation. Electron transporters enhanced dye decolorization. Within 2 h, the addition of 1 μmol/L riboflavin increased the decolorization efficiency from 33.1% to 70.2%. Electron acceptors competed with the DB168 for electrons, thereby inhibiting dye reduction. The addition of 20 mmol/L NaNO3and DMSO reduced decolorization rates to 49.5% and 6.6%, respectively. Through FTIR and LC-MS analysis, it was speculated that the dye molecule preferentially cleaved the azo bonds on both sides to generate aniline and 3,4-diaminophenol, both of which were readily oxidized. This study provides a theoretical basis for the application ofS. oneidensisin bioremediation.

Key words: azo dyes, Shewanella oneidensisMR-1, biodegradation, kinetic fitting, degradation pathway