Optimization of a culture medium for ligninolytic enzyme production and synthetic dye decolorization using response surface methodology

Abstract

A Box-Wilson central composite design was applied to optimize copper, veratryl alcohol and l-asparagine concentrations for Trametes trogii (BAFC 212) ligninolytic enzyme production in submerged fermentation. Decolorization of different dyes (xylidine, malachite green, and anthraquinone blue) by the ligninolytic fluids from the cultures was compared. The addition of copper stimulated laccase and glyoxal oxidase production, but this response was influenced by the medium N-concentration, with improvement higher at low N-levels. The medium that supported the highest ligninolytic production (22.75 U/ml laccase, 0.34 U/ml manganese peroxidase, and 0.20 U/ml glyoxal oxidase) also showed the greatest ability to decolorize the dyes. Only glyoxal oxidase activity limited biodecoloration efficiency, suggesting the involvement of peroxidases in the process. The addition of 1-hydroxybenzotriazole (a known laccase mediator) to the ligninolytic fluids increased both their range and rate of decolorization. The cell-free supernatant did not decolorize xylidine, poly R-478, azure B, and malachite green as efficiently as the whole broth, but results were similar in the case of indigo carmine and remazol brilliant blue R. This indicates that the mycelial biomass may supply other intracellular or mycelial-bound enzymes, or factors necessary for the catalytic cycle of the enzymes. It also implies that this fungus implements different strategies to degrade dyes with diverse chemical structures.