Pathogenic properties of fungal melanins

Melanins are complex black polymers of resonance stabilized cyclic subunits (including indoles, phenols, hydroxynaphthalenes) and are notoriously intr actable to chemical analysis. Cell walls of numerous fungi are melanized, r endering many spores, vegetative hyphae, and certain fruit bodies opaque. M elanin deposition protects the pigmented cell fi-om physical and biological stresses, excludes poisons, and helps limit leakage of certain metabolites . By forming a physical barrier between the cell and its surroundings, the production of a melanized wall layer has a profound effect upon the interac tions between pathogenic fungi and their hosts. In many plane and animal di seases caused by melanotic fungi, melanin biosynthesis is an important dete rminant of pathogenicity and virulence. The mode of action of melanin in th ese diseases is the subject of intensive research, and a variety of mechani sms that link fungal melanin and disease have been discovered.