Inhibition of melanin synthesis in the black yeast Phaeococcomyces sp. by growth on low pH ascorbate medium: production of spheroplasts from "albinized" cells

Abstract

The black yeast Phaeococcomyces sp. produces pentaketide-based melanin constitutively, resulting in a green–black colony colour on commonly used isolation and culture maintenance agar media. Pentaketide melanins are produced by a multi-enzyme pathway, beginning with the cyclization of conjoined acetate molecules and ending with the polymerization of the final phenolic precursor, dihydroxynapthalene, into melanin. A low pH medium, which contains 0.1% ascorbic acid, causes complete inhibition of melanin formation, resulting in a white colony apearance similar to that of albino mutants of Phaeococcomyces sp. Melanized Phaeococcomyces sp. cells resisted enzymatic cell wall digestion, and spheroplasts could not be formed. In contrast, spheroplasts were produced from cells "albinized" by growth on the low pH medium. Inhibition of melanogenesis in other fungi, by growth on low pH ascorbate medium, was found to be specific to pentaketide melanin producers.