Degradation of melanin by Aspergillus fumigatus

Abstract

A strain of Aspergillus fumigatus from composted coffee and garden wastes utilized natural deproteinized insect, banana, hair, octopus, and synthetic tyrosine and dopa melanins as sole sources of carbon. With a sucrose supplement, degradation was essentially complete after 50 days in Czapek medium pH 6.5 at 30 degrees C. The catabolic rate differed for each substrate pigment, as did the molecular weight distribution of products accumulating in the medium. After incubation with L-[U-14C]melanin, over 50% was recovered in a dark fungal pigment, the remainder appearing as cell protein, chitin, lipid, CO2, and polar metabolites. When grown on melanin, the normally pale mycelia darkened with the production of a fungal allomelanin, with infrared spectrum and alkali fusion products differing from those of the substrate pigment. Isotope distribution in amino acids for A. fumigatus grown on labeled melanin supplemented with sucrose suggested separate pools for synthesis of cell proteins and melanoproteins. Deposition of allomelanin increased resistance of conidia, sterigma, and conidiophores to lytic carbohydrases as judged by scanning electron microscopy.