Production, Biochemical Characterization, and Application of Laccase from Halophilic Curvularia lunata MLK46 Recovered from Mangrove Rhizosphere

Laccase production was evaluated in 108 fungal isolates recovered from the eastern coast of Saudi Arabia, a critical element in environmental biodegradation and biotransformation. The most active isolate was identified as <i>Curvularia lunata</i> MLK46 (GenBank accession no. PQ100161). It exhibited maximal productivity at pH 6.5, 30 °C, and incubation for 5 d, with 1% sodium nitrate and 1% galactose as the preferred nitrogen and carbon sources, respectively. Productivity was enhanced by NaCl, CuSO₄, and FeCl₃ supplementation, with a maximum at 0.3 mM, 0.2 mM, and 61.7 mM concentrations, respectively. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) for the purified enzyme through diethylaminoethyl (DEAE)-Sepharose chromatography revealed a prominent band at 71.1 kDa with maximum activity at pH 6 and stability at pH 6-9. Furthermore, it was optimally active at 50 °C and thermally stable at 50-80 °C with a half-life time (<i>T</i>_1/2) of 333.7 min to 80.6 min, respectively. Its activity was also enhanced by many metallic ions, especially Fe³⁺ ions; however, it was inhibited by Hg²⁺ and Ag⁺ ions. The enzyme demonstrated significant degradation of specific substrates such as 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), guaiacol, <i>o</i>-dianisidine, and 2,6-dichlorophenol, with a kinetic efficiency constant which ranged from 40.95 mM^-1 s^-1 to 238.20 mM^-1 s^-1. UV spectrophotometry confirmed efficient oxidation peaks by electron transition against guaiacol (at 300 nm), <i>o</i>-dianisidine (at 480 nm), ABTS (at 420 nm), and 2,6-dichlorophenol (at 600 nm). The results collectively demonstrate the potential of laccase from <i>C. lunata</i> MLK46 as a promising agent for the effective biodegradation of several industrial pollutants under extreme conditions.