The white-rot fungus Trametes versicolor decolorized Amaranth. The hypothesis that the carbon structure of Amaranth was broken down in smaller mass fragments was investigated analyzing the products of decoloration. FTIR spectroscopy, ion chromatography, sulfite and ammonia analysis were used to compare the culture filtrate before dye addition, with the pure dye, the culture filtrate after dye addition, and the culture filtrate during the treatment. The hypothesis of polymerization of the decoloration products was tested by spectrophotometric analysis of dialysates of the pure dye, the culture filtrate before dye addition, and the culture filtrates after dye addition and decoloration. FTIR showed that the signals typical for the azo group disappeared after decoloration, while new peaks appeared that were characteristic of substituted naphthalenic or benzenic compounds. Ion chromatography showed that the level of sulfate in the treatment increased when compared with the level of the sulfate in control, suggesting that the sulfonic groups were being stripped from Amaranth's structure and metabolized to sulfate. Sulfite measurements for the treatment and controls showed no significant difference, and were well below the saturation concentration for sulfite in water, confirming that the medium was aerobic. Ammonia concentration did not change with the decoloration. Absorbance scans after dialysis of decolorized samples showed no new peaks, suggesting that the decoloration products were not polymerized. These observations suggests that the decoloration mechanism starts with the azo link removal, followed by desulfonation, naphthalene ring opening, and the formation of smaller mass fragments, similar to fungal metabolites.

Trametes versicolor decolorized 2000 mg L(-1) of the mono-azo substituted naphthalenic dye Amaranth with no dye sorption observed visually. The changes in the toxicity were assessed over a period of 30 d for the dye-treated viable culture, control (no dye added), and a boiled culture treated with dye, using the Microtox Acute Toxicity assay. Before dye addition, the culture filtrate had some toxicity, which increased after the dye addition. The toxicity of the dye-treated culture decreased during the treatment. The loss of toxicity occurred at the same time, with the loss of color suggesting that detoxification is associated with decoloration. The change in pH was due to natural metabolic processes and had a small effect on detoxification. Because the toxicity of the treatment was similar to that of the control at the end of the treatment, the effluent seems to be safe for release into the environment, potentially rendering this treatment suitable for industrial application.

The white-rot fungus Trametes versicolor decolorized the mono-azo-substituted naphthalenic dye Amaranth. The relationship between the amount of enzymes present in the system and the efficiency of the decoloration process was investigated. The two responses used to quantify the process of decoloration (i.e., initial decoloration rate, v0, and the percent concentration of dye decolorized in 1 h, %c) were correlated with the amount of three enzymes considered for the study (lignin peroxidase, manganese peroxidase, and laccase) and analyzed through stepwise regression analysis (forward, backward, and mixed). The results of the correlation analysis and those of the regression analysis indicated that lignin peroxidase is the enzyme having the greatest influence on the two responses.