Biodecolourisation and biodegradation of leather dyes by a native isolate of Trametes villosa

Abstract

Dyeing is an important step in the leather manufacture process. Effluent from this stage contains some types of synthetic dye that may be a threat to the environment and human health. Biological treatment of dye-containing wastewaters by microorganisms has been presented as a cost effective and promising environmentally friendly alternative. In the present work, the potential of Brazilian native white-rot fungi strains, collected and screened to produce extracellular ligninolytic enzymes, was evaluated for the biodecolourisation and biodegradation of different azo tannery dyes. The strain SCS-10 showed high activity of ligninolytic enzymes and allowed the colour removal of dyes in solid media. This isolate was characterised morphologically and identified as Trametes villosa, based on a molecular analysis of the internal transcribed spacer (ITS) region sequences. T. villosa SCS-10 showed high biodecolourisation efficiency for the dyes assessed, achieving 95.71 ± 1.29, 92.76 ± 0.99 and 96.84 ± 1.39% for Acid Red 357, Acid Black 210 and Acid Blue 161, respectively, at 100 mg L−1, 30 °C, pH 5.5 and 150 rpm, within 168 h of treatment. Remarkable peaks of laccase activity (1150–1550 U L−1) were observed during specific periods in the biodecolourisation process. The complete inhibition of Lac activity by sodium azide (NaN3, 0.1 mM) led to biodecolourisation values of 13.29 ± 0.93, 12.30 ± 0.46 and 20.05 ± 2.08% for AR357, AB210 and AB161, respectively. These results confirmed the main role of laccase in colour removal, although biosorption also had a minor involvement in biodecolourisation. In vitro assays also showed the efficiency of decolourisation of the leather dyes. The enzymatic crude extract produced by T. villosa allowed 85.45 ± 3.43 (AR357), 76.96 ± 1.39 (AB210) and 90.17 ± 0.97% (AB161) of biodecolourisation when enhanced by the use of the redox mediator 1-hydroxybenzotriazol (HBT, 1 mM). UV–vis and FTIR spectral analyses confirmed the occurrence of enzymatic biodegradation as the mechanism responsible for colour removal. T. villosa SCS-10 was able to tolerate high concentrations of the dyes (200–1000 mg L−1) and a wide range of pH (4.0–8.0) during biodecolourisation. The native isolate T. villosa SCS-10 is considered a suitable candidate for the treatment of dye-polluted wastewater from the leather industry due to the mechanisms of enzymatic biodegradation and biosorption.