Melanin: Properties, Biosynthesis and its Role as Virulence in Fungi: A Review

Melanin in fungi has been postulated to be involved in a wide range of virulence-associated properties which include interactions with the hosts, oxidative stresses, UV light and hydrolytic enzymes, resistance to antifungal agents, iron-binding activities and even the harnessing of ionizing radiation in contaminated soils. Melanin is found to be a secondary metabolite as it is produced after the cessation of active growth of fungus. They play an important role in fungal pathogenesis. In Colletotrichum lagenarium and Magnaporthe grisea, melanins are essential for infectivity, as they allow enormous pressure to build in appressoria, enabling the fungus to penetrate plant leaves. Fungal melanin diversity was reported to occur through two biosynthetic pathways. Melanized fungi more effectively prevent diffusion of glycerol which retains a higher turgor pressure necessary for the degradation of the cuticle. A notable example of this phenomenon is the fungus M. grisea which utilizes melanin to invade rice plants and result in rice blast disease.