Decolorization of textile reactive dyes by the crude laccase produced from solid-state fermentation of agro-byproducts

Degradation of a leather-dye by the combination of depolymerised wood-chip biochar adsorption and solid-state fermentation with Trametes villosa SCS-10

Adsorption into biochar-derived materials and mycoremediation are promising technologies for removing dyes from solid and liquid matrices. This study presents a combined treatment with adsorption into wood-chip biochar and mycodegradation under solid-state fermentation by Trametes villosa for removing the leather-dye Acid Blue 161. In the first stage, untreated wood-chip biochar, NaOH–depolymerised biochar and KMnO4–depolymerised biochar were assessed for their dye removal efficiency by adsorption. KMnO4–depolymerised biochar exhibited the highest adsorption (85.1 ± 1.9%) after 24 h of contact. KMnO4–depolymerisation modified some physical and chemical properties on the untreated wood-chip biochar, increasing the surface area (50.4 m2 g–1), pore size (1.9 nm), and presence of surface functional groups. Response surface methodology coupled with a Box–Behnken design was used to optimise the AB161 adsorption into the KMnO4–depolymerised biochar. The optimised conditions, pH 3.0, dye concentration 100 mg L–1 and sorbent dosage 2 g L–1, led to a higher dye removal efficiency by adsorption (91.9 ± 1.0%). In a second stage, the wood-chip biochar supplemented with nutrients (1% malt extract and 0.5% peptone) was employed as a solid matrix for growing T. villosa and regenerating the dye-saturated material. After 15 days, T. villosa was able to grow (86.8 ± 0.8%), exhibit laccase activity (621.9 ± 62.3 U L–1), and biodegrade (91.4 ± 1.3%) the dye adsorbed into the KMnO4–depolymerised biochar. Finally, the mycoregenerated biochar was reutilised in a new cycle of adsorption reaching 79.5 ± 2.0% of dye removal efficiency by adsorption. This study revealed the potential of the combined treatment and is an initial assessment for developing commercial alternatives for treating leather industry wastewaters.

Elucidation of fungal dye-decolourizing peroxidase (DyP) and ligninolytic enzyme activities in decolourization and mineralization of azo dyes

AIM

The aim of the study is to investigate the efficiency of Geotrichum candidum in the decolourization and mineralization of synthetic azo dyes.

METHODS AND RESULTS

It includes screening of enzymes from G. candidum and its optimization, followed by decolourization and mineralization studies. Decolourization was observed to be maximum in methyl orange (94·6%) followed by Congo red (85%), trypan blue (70·4%) and Eriochrome Black T (55·6%) in 48 h, suggesting the plausible degradation of the azo dyes by G. candidum. The enzyme activity study showed that DyP-type peroxidase has highest activity of 900 mU ml^-1 compared to that of laccase (405 mU ml^-1 ) and lignin peroxidase (LiP) (324 mU ml^-1 ) at optimized pH (6) and temperature (35°C). Moreover, the rate of decolourization was found to be directly proportional to the production of laccase and LiP, unlike DyP-type peroxidase. Furthermore, mineralization study demonstrated reduction in aromatic amines, showing 20% mineralization of methyl orange.

CONCLUSION

Geotrichum candidum with its enzyme system is able to efficiently decolourize and mineralize the experimental azo dyes.

SIGNIFICANCE AND IMPACT OF THE STUDY

The efficient decolourization and mineralization of azo dyes makes G. candidum a promising alternative in the treatment of textile effluent contaminated with azo dyes.

Induction, expression and characterisation of laccase genes from the marine-derived fungal strains Nigrospora sp. CBMAI 1328 and Arthopyrenia sp. CBMAI 1330

The capability of the fungi Nigrospora sp. CBMAI 1328 and Arthopyrenia sp. CBMAI 1330 isolated from marine sponge to synthesise laccases (Lcc) in the presence of the inducer copper (1–10 μM) was assessed. In a liquid culture medium supplemented with 5 μM of copper sulphate after 5 days of incubation, Nigrospora sp. presented the highest Lcc activity (25.2 U·L⁻¹). The effect of copper on Lcc gene expression was evaluated by reverse transcriptase polymerase chain reaction. Nigrospora sp. showed the highest gene expression of Lcc under the same conditions of Lcc synthesis. The highest Lcc expression by the Arthopyrenia sp. was detected at 96 h of incubation in absence of copper. Molecular approaches allowed the detection of Lcc isozymes and suggest the presence of at least two undescribed putative genes. Additionally, Lcc sequences from the both fungal strains clustered with other Lcc sequences from other fungi that inhabit marine environments.

Biochemical response to exposure to six textile dyes in early developmental stages of Xenopus laevis

The present study was undertaken to determine the toxic effect of a lethal concentration of six different commercially used textile dyes on the 46th stage of Xenopus laevis tadpoles. The tadpoles were exposed to Astrazon Red FBL, Astrazon Blue FGRL, Remazol Red RR, Remazol Turquoise Blue G-A, Cibacron Red FN-3G, and Cibacron Blue FN-R for 168 h in static test conditions, and thus, 168-h median lethal concentrations (LC(50)s) of each dye were determined to be 0.35, 0.13, 112, 7, 359, and 15.8 mg/L, respectively. Also, to evaluate the sublethal effects of each dye, tadpoles were exposed to different concentrations of dyes (with respect to 168-h LC(50)s) for 24 h. The alteration of selected enzyme activities was tested. For this aim, glutathione S-transferase (GST), carboxylesterase, and lactate dehydrogenase (LDH) were assayed. After dye exposure, the GST induction or inhibition and LDH induction indicated some possible mechanisms of oxidative stress and deterioration in aerobic respiration processes induced by the tested dyes. Findings of the study suggest that selected biomarker enzymes are useful in understanding the toxic mechanisms of these dyes in X. laevis tadpoles as early warning indicators. Therefore, these selected biomarkers may evaluate the effect of environmental factors, such as textile dye effluents and other industrial pollutants, on amphibians in biomonitoring studies.