A low-cost wheat bran medium for biodegradation of the benzidine-based carcinogenic dye Trypan Blue using a microbial consortium

Abstract

Environmental release of benzidine-based dyes is a matter of health concern. Here, a microbial consortium was enriched from textile dye contaminated soils and investigated for biodegradation of the carcinogenic benzidine-based dye Trypan Blue using wheat bran (WB) as growth medium. The PCR-DGGE analysis of enriched microbial consortium revealed the presence of 15 different bacteria. Decolorization studies suggested that the microbial consortium has high metabolic activity towards Trypan Blue as complete removal of 50 mg∙L-1 dye was observed within 24 h at 30 ± 0.2 °C and pH 7. Significant reduction in TOC (64%) and COD (88%) of dye decolorized broths confirmed mineralization. Induction in azoreductase (500%), NADH-DCIP reductase (264%) and laccase (275%) proved enzymatic decolorization of dye. HPLC analysis of dye decolorized products showed the formation of six metabolites while the FTIR spectrum indicated removal of diazo bonds at 1612.30 and 1581.34 cm-1. The proposed dye degradation pathway based on GC-MS and enzyme analysis suggested the formation of two low molecular weight intermediates. Phytotoxicity and acute toxicity studies revealed the less toxic nature of the dye degradation products. These results provide experimental evidence for the utilization of agricultural waste as a novel low-cost growth medium for biodegradation of benzidine-based dyes, and suggested the potential of the microbial consortium in detoxification.

Figure 1

Structure of the benzidine-based azo dye Trypan Blue.

Figure 2

DGGE pattern of the PCR amplified 16S rDNA genes of enriched microbial consortium (a) before and (b) after decolorization of dye Trypan Blue (50 mg∙L⁻¹).

Figure 3

UV-visible overlay spectra of dye Trypan Blue and its ethyl acetate extracted decolorized products after 24 h treatment with microbial consortium.

Figure 4

Effect of microaerophilic and aerobic (shaking at 120 rpm) conditions on decolorization of dye Trypan Blue (50 mg∙L⁻¹) by microbial consortium at 30 ± 0.2 °C, pH 7.0.

Figure 5

Effect of environmental parameters on decolorization of Trypan Blue (50 mg∙L⁻¹) by microbial consortium; (a) initial pH of pre-enriched culture medium, (b) incubation temperature, (c) various dye concentration. Decolorization was measured after 24 h of incubation. Data points represents the mean of three independent replicates, standard error of mean is indicated by error bars.

Figure 6

HPLC elution profile of (a) control dye Trypan Blue and (b) its degradation product at 210 nm.

Figure 7

FTIR analysis of a Trypan Blue control and its degradation products obtained after 24 h treatment with the microbial consortium.

Figure 8

Possible degradation mechanism of Trypan Blue by the microbial consortium based on the GC-MS data and enzyme activities.