The dye solution containing 50 mg L−1 MG was pretreated with Trametestrogii Berk S0301 laccase (1 U mL−1) or the same amount of a heat-denatured laccase at 30 °C for 8 h. The pretreated MG solutions were filtered through a 0.45 μm membrane filter and used for the toxicity assay. To assay phytotoxicity, wheat seeds were surface sterilized with 0.1% mercuric chloride and sown on Murashige and Skoog (MS) agar plates. After growing at 20 °C for 4 d, the early seedlings were transferred to MS plates with 15 mg L−1 MG treated by the crude laccase or by the heat-denatured crude laccase. Wheat seedlings and root lengths were observed every 24 h. Each treatment contained three plates, and each plate contained 10 seeds. To assay microbial toxicity, the MA plates with 15 mg L−1 MG treated by the crude laccase or by the heat-denatured crude laccase were inoculated with agar disks (5 mm diameter) of actively growing mycelia of strain Trametes hirsute (Wulf.: Fr.) Pilat S0296. The cultures were incubated at 30 °C, and the diameter of the colony on each plate was recorded every day.