Removal of chlorophenolic derivatives by soil isolated ascomycete of Paraconiothyrium variabile and studying the role of its extracellular laccase

The ability of Paraconiothyrium variabile, a laccase producing ascomycete recently isolated from soil, was studied to eliminate chlorophenol derivatives in submerged culture medium. Among the tested compounds, ρ-chlorophenol (ρ-CP) and pentachlorophenol (PCP) were found to have minimum and maximum toxic effects, respectively, on the growth of the microorganism and at the same time high and low bioelimination percentages. The fungal strain was able to remove 86% of ρ-CP (with initial concentration of 40 mg l(-1)) and 56% of 2,4-dichlorophenol (2,4-DCP; with same concentration as ρ-CP) after 9 days of incubation while no elimination was observed in the presence of 2,4,6-trichlorophenol (2,4,6-TCP) and PCP. Monitoring of laccase production level in the fermentation broth together with pollutant removal confirmed the key role of this copper-containing oxidase in chlorophenol derivatives elimination. The type of laccase inducer (guaiacol) and its final concentration (250 μM) and also initial pH of the fermentation broth (pH=5.5) in the elimination of ρ-CP increased the final removal yield from 86% to 94.3%.

Dechlorination of chlorinated compounds by Trametes versicolor ATCC 200801 crude laccase and quantitative structure-activity relationship of toxicity

Chlorinated compounds constitute an important class of xenobiotics. Crude laccase was produced using Trametes versicolor ATCC (200801) in potato dextrose broth, with wheat bran as an inducing medium, and its ability to dechlorinate eight compounds was determined. The compounds were 2-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, 2,6-dichlorophenol, 2,4,5-trichlorophenol, 2,4,6-trichlorophenol, heptachlor and pentachlorophenol. A range of parameters for the dechlorination of some compounds was tested, including incubation period, pH, initial substrate concentration, temperature, and enzyme quantity. The oxygen consumption was determined during each dechlorination process, under pre-determined optimum conditions. The changes in chemical structure of the compounds were also determined, by using FTIR analysis, following dechlorination of test chlorophenolics. Strong interactions were found to lead to the reactivity of hydroxyl groups in some cases and chlorine atoms were released from the benzene ring. The changes in compound toxicity were monitored before and after enzymatic treatment, using Microtox. Quantitative structure-activity relationships for the toxicity of the chlorinated compounds were developed. Consequently, the toxic activity of the test compounds was controlled by electrophilic index and electronic properties.