Studies on the biosynthetic pathways of melanin in Auricularia auricula

Melanin is a natural pigment ubiquitously present in living organisms, including bacteria, fungi, plants, and animals. Melanin produced by the edible mushroom Auricularia auricula has a remarkable potential for resource development. Several A. auricula strains planted across China were collected and analyzed for mycelial growth rate and colony red, green, blue (RGB) value for color block. Further, the effects of various nutrients on melanin formation, including different carbon and nitrogen sources were evaluated to optimize the medium for submerged fermentation. The pathways involved in the biosynthesis of melanin in A. auricula were investigated using an enzyme inhibitor assay and intermediate determination. In addition, the functional activity of purified A. auricula melanin was assessed. The highest melanin yield (1.797 g/L) was displayed by strain AU-3 in medium I. A. auricula melanin was composed of eumelanin, pheomelanin, and 1,8-dihydroxynaphthalene melanin, and the biosynthetic pathways involved were Raper–Mason and 1,8-dihydroxynaphthalene melanin pathway. In addition, melanin purified from A. auricula exhibited substantial antioxidant, antibacterial, and antitumor activities.