DECOLORIZATION OF CRYSTAL VIOLET BY CRUDE LACCASE FROM TRAMETES SP. LH-3 UNDER SOLID-STATE FERMENTATION BY POLYMERIZATION REACTIONS.

In this study, dye decolorizing potential of crude enzyme from Trametes sp. LH-3 was demonstrated towards crystal violet (CV) by polymerization reactions. Trametes sp. LH-3 produced laccase as the dominant lignolytic enzyme during solid state fermentation (SSF) of wheat straw, an agroindustry waste. Native polyacrylamide gel electrophoresis (PAGE) confirms that crude enzyme contained two laccase isoforms which were the major enzymes involved in decolorization of CV. The dye (5 mg L^-1) was decolorized by 50% within 24 h by the crude laccase (10 U. ml^-1) alone, but more efficiently in the presence of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a redox mediator, showing 93.5% decolorization within 12 h. Increasing the ABTS concentration can improve the decolorization rates, but 10 μM ABTS was sufficient for maximum decolorization of CV (5 mg L^-1) by the crude laccase and excessive redox mediators resulting in activity inhibition of laccase. During the decolorization reaction, the characteristic absorption peak of the dye around 589 nm decreased rapidly with slight blue shifts (559 nm), and some dark-colored precipitates were formed in the samples. Characterization of CV transformation products by UV-VIS and FT-IR analyses revealed that N-demethylation and poly-merization were the key mechanisms of decolorization of CV by laccase. The results of the present study suggested that the application of crude laccase and effective mediators that are easily available and inexpensive could overcome its drawbacks in dye effluent treatment. [ABSTRACT FROM AUTHOR]