Biodegradation of the Fe-Complex Diazo Dye Acid Brown 452 by a Defined Bacterial Consortium

Abstract Metal-complex azo dyes in textile and tanning wastewater resist conventional treatment and release both color and toxic metal into receiving waters. Yet, most biological systems perform poorly at industrial dye loads and do not address the coordinated metal. This study reports the first biodegradation of the iron-complex diazo dye Acid Brown 452 (ABr452) by a defined three-member bacterial consortium (Consortium-G) isolated from dye-contaminated effluent. Sequential statistical optimization increased decolorization to 86% at 500 mg L–1, and measurable activity was retained up to 7,000 mg L–1, approximately an order of magnitude above limits generally reported for bacterial systems. Consortium-G additionally removed more than 90% of dye-associated iron through degradation-coupled biosorption, in which enzymatic azo-bond cleavage releases iron for retention by the biomass. Spectroscopic and chromatographic analyses demonstrated extensive structural breakdown, and pathway enrichment analysis identified benzoate degradation as the only significantly enriched route, indicating channeling of dye-derived aromatic intermediates into the β-ketoadipate pathway. Time-resolved enzyme profiling revealed a biphasic mechanism of reductive azo-bond cleavage followed by oxidative ring opening. These findings establish an integrated process combining high dye tolerance with simultaneous chromophore and metal removal. This study did not assess the toxicity of the degradation products.