Melanin synthesis by Sclerotinia sclerotiorum.

We confirmed that the melanin produced by Sclerotinia sclerotiorum is a dihydroxynaphthalene (DHN). The specific DHN melanogenesis inhibitor test that uses tricyclazole at low levels (typically 2-5 ppm) to cause a confirmatory appearance of soluble red-brown inhibition products does not work when analyzing melanin synthesis in the sclerotia of S. sclerotiorum. We demonstrated the presence of scytalone dehydratase, an enzyme specific to DHN melanogenesis, in melanized sclerotia and melanized nonsclerotial mycelia and observed formation of mycelial nonsclerotial melanin when the fungus was grown on the surface of sterilized dialysis membrane or in rich organic media. Nonsclerotial melanized hyphae in wild type and mutant strains showed the typical excretion of pigmented inhibition products of the DHN pathway in the presence of tricyclazole, and one of these products, 2-hydroxyjuglone, was identified by thin layer chromatography and spectroscopy. We report basic conditions for sclerotial melanin degradation by the white rot fungus Phanerochaete chrysosporium.