Laccase-producing fungal strains from pesticide-farmland soil: Evaluating their heavy metal tolerance

Indiscriminate pesticide applications allow metals to accumulate in soils and crops, endangering human health, environment and food security. This study examines the metal removal potential by laccase-producing fungi. Five inorganic soil samples were collected from farmland. Soil aliquot was inoculated into sterile potato dextrose agar plates and fungi were identified based on their macroscopic, microscopic and molecular techniques. Laccase production was screened using a tannic acid indicator, and the guaiacol assay measured laccase activities. Metal tolerance was assessed for lead (Pb) and arsenic (As) at concentrations of 5 to 20 g/L. Fourteen isolates that belong to the genera of Candida (14%), Trichoderma (21%), Trichosporon (22%), Aspergillus (36%) and Rhodotorula (7%) were obtained. Only Aspergillus niger and Aspergillus japonicus demonstrated laccase production. A. niger exhibited highest enzyme activity (0.8026U/mL) while the least laccase activity (0.1453U/mL) was produced by A. japonicum. The optimal As and Pb tolerances of A. niger are 5 g/L and 10 g/L, respectively. A. japonicus showed stronger tolerance up to 15 g/L for Pb, whereas that of As remains 5 g/L. These results demonstrate that A. niger and A. japonicus hold promise as valuable bio-resources due to their effective laccase production and notable metal tolerance, underscoring their potential applications in bioremediation.