Melanin pigment synthesized by microorganisms during hydroxylation and polymerization of organic compounds, was an attractive choice for commercial scale production. In this study, optimization parameters of certain environmental conditions (incubation periods, pH, temperature and shaking speed) and certain nutritional requirements ( carbon, nitrogen, metals and amino acids sources) that influencing melanin production by Aspergillus oryzae were performed. Also, the effects of different surfactants and some L-tyrosine natural sources on melanin production were studied. To economize melanin production, cheaper waste sources, such as banana peel at 2%, were used as carbon source , 5% yeast extract as a nitrogen source, (0.2mM) copper sulphate as activated metal, 0.1% L-methionine, 0.1% Tween 80 as a surfactant and contained, in g/l: K2HPO4 2.5, CaCl2 H2O 0.5, MgSO4.7H2O 1.0, in addition to 0.1% L-tyrosine. Highly significant melanin (9.083 mg/ml) yield with tyrosinase activity (568 U/ml) was reached at optimization conditions. The stimulated eco-friendly synthesis and stabilization of silver nanoparticles (AgNPs) by the characterized melanin as reducing agent using radio lytic reactions of gamma radiation(10 kGy), demonstrate the metal interacting nature of pigment.The melanin incorporation into AgNPs was confirmed by UV-visible, dynamic light scattering (DLS), FT-IR and XRD spectrophotometers. Transmission electron microscope (TEM) analysis revealed morphology of well dispersed spherical AgNPs with mean diameter of 20.74 nm. The synthesized AgNPs exhibited good antibacterial activity against some pathogenic Gram positive and Gram negative bacteria, also anti candida, that can find potential applications in the cosmetic and pharmaceutical industries.
