Novel bacterial biofilm consortia that degrade and detoxify the carcinogenic diazo dye Congo red.

Free-living planktonic single bacterial strain can decolorize Congo red (CR) but often produces the carcinogenic, mutagenic and genotoxic aromatic amines. Planktonic single and bacterial consortia are more susceptible to toxic pollutants than their biofilm counterparts. In the present study, four biofilm consortia (C1 = Vitreoscilla sp. ENSG301, Acinetobacter lwoffii ENSG302, Klebsiella pneumoniae ENSG303 and Pseudomonas fluorescens ENSG304, C2 = Escherichia coli ENSD101, Enterobacter asburiae ENSD102 and E. ludwigii ENSH201, C3 = E. asburiae ENSD102, Vitreoscilla sp. ENSG301 and Bacillus thuringiensis ENSW401, and C4 = E. coli ENSD101, E. ludwigii ENSH201 and B. thuringiensis ENSW401) were prepared and assessed for bioremediation of CR. All these biofilm consortia remarkably decolorized (96.9 to 99.5%) the CR (100 mg/L) in static condition within 72 h incubation at 28 °C. These consortia also synthesized significantly more intracellular azoreductase and laccase enzyme than extracellular of these enzymes. UV-Vis spectral analysis revealed that the major peak at 478 nm wavelength of CR was completely disappeared. FTIR analysis showed several major peaks along with azo bonds are completely or partly disappeared, deformed or widened. Chemical oxygen demand was reduced by 86.4, 85.5, 87.0 and 86.2% by C1, C2, C3 and C4, respectively. Accordingly, biodegraded metabolites of CR by different biofilm consortia did not inhibit the germination of wheat seeds and bacterial growth. Thus, these biofilm consortia can be applied in bioremediation of wastewater containing CR for safe disposal into the environment. To our knowledge, this is the first report on degradation and detoxification of aqueous solution containing CR by bacterial biofilm consortia.