Green Synthesis and Antibacterial Activities of Silver Nanoparticles Using Extracellular Laccase of <i>Lentinus edodes</i>

This study reports the multi-step mutagenesis of Lentinus edodes towards optimization of the production of laccase and novel application of laccase in the biosynthesis of silver nanoparticles (AgNPs) which could be used to develop an eco-friendly method for the rapid biosynthesis of AgNPs. The wild strain of L. edodes was subjected to UV irradiation at 254 nm and the resultant viable mutant was further treated with acridine orange, a chemical mutagen. The strains were evaluated for the production of laccase and the crude laccase of the UV mutant (UV 10 ) was used for the green synthesis of AgNPs. The particles were characterized by UV-Visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). Laccase activities of wild, UV 10 and UV 10 ACR 8 strains of L. edodes were obtained as 2.6, 10.6 and 2.8 U/ml/min respectively after 7 days of fermentation, showing laccase yield improvement of 4.08-fold for UV 10 mutant. UV-Visible spectroscopy indicated the formation of AgNPs at absorption band of 430 nm. FTIR result indicated that proteins were responsible for AgNP synthesis, while SEM analysis confirmed the formation of walnut-shaped nanoparticles with size range of 50-100 nm. The biosynthesized nanoparticles revealed effective inhibition against clinical isolates of Escherichia coli , Pseudomonas aeruginosa and Klebsiella pneumoniae . To the best of the authors’ knowledge, this result represents the first report on the biosynthesis of AgNPs using L. edodes metabolite . The report adds to the growing relevance of L. edodes as potential industrially viable organism, used for diverse biotechnological applications.