An alkaline fungal laccase overexpressed in Coprinopsis cinerea shows application potential in treating high-salt dye wastewater

[Objective] To homologously overexpress an alkaline fungal laccase PIE5 (CcPIE5) in Coprinopsis cinerea FA2222 under the control of the Agaricus bisporus gpdII promoter. [Methods] The laccase activity reached (24.2±1.1) U/mL in the supernatant after 7 days of cultivation at 37 ℃ in the mKjalke medium. The purified CcPIE5 showcased the best performance at pH 8.0 and 60 ℃. [Results] Unlike other characterized fungal laccases, CcPIE5 was tolerant to high concentrations of NaCl. Particularly, both k cat and K m decreased when the concentration of NaCl was increased from 0 to 1.5 mol/L, which indicated that CcPIE5 demonstrated application potential in the dye decoloring of texile finishing. In dye decolorization, CcPIE5 efficiently degraded (92.9±2.3)% indigo carmine at pH 8.5 and 60 ℃, with syringic acid as the mediator. Isatin 5-sulfonic acid (ISA) was identified by LC-MS as the primary byproduct of indigo carmine degradation. [Conclusion] CcPIE5 is best-suited in decolorizing dyes under high temperatures and alkaline and salty conditions. It serves as a good candidate for specific applications in the environment and industry.