Laccase chloride inhibition reduction by an anthraquinonic substrate.

Due to their low substrate specificity, fungal laccases have a great potential in industrial applications, including the bioremediation of colored wastewaters from textile industry. However, the presence of halides in these effluents (up to 1M NaCl) which inhibit laccases is a drawback for bioremediation processes. In order to develop an efficient enzymatic remediation process for textile dye effluent, the possibility to reduce this halide inhibition is conditioned by a better understanding of the phenomenon. The present study gives a detailed account of the kinetics of chloride inhibition of both ABTS (a model substrate) and ABu62 (an anthraquinonic acid dye) oxidations catalyzed by Trametes versicolor laccase (LacIIIb). Chloride inhibition can be described by a mixed model for ABTS and a non-competitive model for ABu62 and both inhibitions are linear suggesting a single inhibitory site for chloride. Experiments were also conducted in presence of both substrates. An apparent activation of laccase was observed in the presence of ABu62 leading to an enhancement of the oxidation rate of ABTS. The extent of activation increased in the presence of chloride anions. Finally, for the first time to our knowledge, we evidenced that inhibition of ABTS oxidation by chloride can be reduced in the presence of ABu62.

Decolorization, cytotoxicity, and genotoxicity reduction during a combined ozonation/fungal treatment of dye-contaminated wastewater.

In view of compliance with increasingly stringent environmental legislation imposed by regional, national, and supranational (e.g., European Union) authorities, innovative environmental technologies for the treatment of dye-contaminated effluents are necessary in the color industry. In this study, effluents of an industrial dye producer were subjected to distinct treatment trains following an initial qualitative characterization. The effectiveness of ozonation and a treatment using white rot fungi (WRF) and their enzymes were compared with respect to parameters such as residual color, toxicity on human cells, and genotoxicity. A combined ozonation/WRF process was also investigated. The effluent exhibited significant toxicity that was reduced by only 10% through ozonation, whereas the fungal treatment achieved a 35% reduction. A combined treatment (ozone/WRF) caused an abatement of the toxicity by more than 70%. In addition, the initial genotoxicity of the effluent was still present after the ozone treatment, while it was completely removed through the fungal treatment.

Coupling occurs before breakdown during biotransformation of Acid Blue 62 by white rot fungi.

Only few data exist on the metabolites produced during the biotransformation of anthraquinonic dyes by white rot fungi (WRF). During the biotransformation of an anthraquinonic dye Acid Blue 62 (ABu62) using Pycnoporus sanguineus MUCL 41582 strain, it was previously demonstrated that the blue colour of the medium turned to red before complete dye decolourisation. To better understand the phenomenon, this study carried out ABu62 biotransformation with five different WRF strains (Coriolopsis polyzona MUCL 38443, Perenniporia ochroleuca MUCL 41114, Perenniporia tephropora MUCL 41562, P. sanguineus MUCL 38531 and Trametes versicolor MUCL 38412) and compared with P. sanguineus MUCL 41582 previously described. A multi-methodological approach (using capillary electrophoresis, mass spectrometry, HPLC, UV, NMR and IR spectroscopies) was developed to characterise the metabolites involved and monitor their apparition. Seven metabolites were commonly found with all strains, suggesting a common metabolic pathway for ABu62 biotransformation. During the first days, dimer and oligomers of the initial ABu62 molecule were observed: the main one absorbed in the 500nm region, explaining the red colour appearance of the medium. This main metabolite was made up of two molecules of ABu62 linked by an azo bond, minus a cyclohexyl moiety. After a longer incubation time, breakdown products were observed. Based on these products characterizations, a bioconversion pathway was proposed.

Beta-glucosidase-catalyzed hydrolysis of indican from leaves of Polygonum tinctorium.

In this article, a HPLC method to identify and quantify the dyes and the indigo precursors produced in Polygonum tinctorium is described. Using this technique, indican has been positively identified in extracts of P. tinctorium. Our work with two cultivars of P. tinctorium has confirmed that the quantity of indican is dependent on the cultivars, harvest period, and age of the leaves. Two enzymes, Novozym 188 (cellobiase) and Novarom G (beta-glucosidase), are compared on the basis of their activities to hydrolyze the indican at several pH values. We observed that Novarom G is more active than Novozym 188 whatever the pH and that optimum pH of both enzymes for indican hydrolysis is 3. Liberated indoxyl can be oxidized in alkaline media and transformed into indigo and indirubin.