Partial purification and characterization of a thermophilic and alkali-stable laccase of Phoma herbarum isolate KU4 with dye-decolorization efficiency

Abstract

Production of an extracellular thermophilic and alkali stable laccase from Phoma herbarum isolate KU4 was reported for the first time, both in submerged fermentation (SmF, highest 1590 U/mL) and solid state fermentation (SSF, highest 2014.21 U/mL) using agro-industrial residues. The laccase was partially purified to 7.93 fold with the apparent molecular weight of 298 kDa. The enzyme had pH optimum at 5.0 and temperature optimum at 50 °C, with maximum stability at pH 8.0. It showed activity towards various phenolic and non-phenolic compounds. The kinetic parameters, K_m, V_max and K_cat of the laccase for DMP were 0.216 mM, 270.27 U/mg and 506.69 s⁻¹, respectively. Laccase activity was inhibited by various metal ions and conventional inhibitors, however, it was slightly increased by Zn²⁺. The laccase showed good decolorization efficiency towards four industrial dyes, namely, methyl violet (75.66%), methyl green (65%), indigo carmine (58%) and neutral red (42%) within 24 h. FTIR analysis of the decolorized products confirmed the degradation of the dyes. The decolorization efficiency of the enzyme suggests that the partially purified laccase could be used to decolorize synthetic dyes present in industrial effluents and for waste water treatments. The thermophilic and alkali stable laccase may also have wider potential industrial applications.

Keywords:

• Agro-industrial residues
• alkali-stable
• laccase
• protease
• Phoma herbarum isolate KU4
• thermophilic

Disclosure statement

The authors have no conflicts of interest in financial or commercial issues of the present research work or its publication.

Additional information

Funding

All the authors acknowledge the Personal Research Grant and DST-PURSE programme fund provided by University of Kalyani for the financial assistance necessary for the paper.