Functions of fungal melanin beyond virulence

Abstract

Melanins are ancient biological pigments found in all kingdoms of life. In fungi, their role in microbial pathogenesis is well established; however, these complex biomolecules also confer upon fungal microorganisms the faculty to tolerate extreme environments such as the Earth’s poles, the International Space Station and places contaminated by toxic metals and ionizing radiation. A remarkable property of melanin is its capacity to interact with a wide range of electromagnetic radiation frequencies, functioning as a protecting and energy harvesting pigment. Other roles of fungal melanin include scavenging of free radical, thermo-tolerance, metal ion sequestration, cell development, and mechanical-chemical cellular strength. In this review, we explore the various functions ascribed to this biological pigment in fungi and its remarkable physicochemical properties.

Purification and characterisation of a sulphur rich melanin from edible mushroom Termitomyces albuminosus Heim

“…Some fungi undergo melanogenesis in response to certain environmental stress conditions such as extreme temperatures, dessiccation, hyperosmotic conditions, limited nutrients, pH changes, metal toxcicity, UV or ionisation stress, action of antagonistic microbes. Melanisation in fungi mostly seen in hyaline hyphae, sclerotia, appressoria, reproductive structures or conidia (Cordero and Casadevall 2017). Hyphal melanin is often found to be deposited as the outermost layer or internal layer in cell wall only with age or other stress (Bell and Wheeler 1986; Henson et al 1999; Butler et al 2001).…”

Endolichenic fungi: the lesser known fungal associates of lichens

“…Lichens also accumulate heavy metals and radionuclides (Gadd 2007). Although fungi are known to weather rocks by producing carbonic and other acids (Hoffland et al 2004) and scavenge heavy metals and tolerate radionuclides (Cordero and Casadevall 2017), the contribution of endolichenic fungi to these phenomena exhibited by lichens is not known.…”

Natural selection drives population divergence for local adaptation in a wheat pathogen

“…The ecological roles associated with fungal melanin vary widely among 436 species (Butler & Day, 1998), but it is most often reported to be related to virulence, 437 competition with other microbes, protection against UV-light and toxic compounds, and 438 tolerance of extreme temperatures (Nosanchuk & Casadevall, 2003;Dadachova et al, 439 2007;Hagiwara et al, 2017). Although melanin is thought to provide protection against 440 cold and heat stress (Rehnstrom & Free, 1996;Paolo et al, 2006), there are exceptions 441 (Wheeler & Bell, 1988), and information regarding its impact on fungal thermal tolerance 442 remains scarce (Cordero & Casadevall, 2017). Melanin production is energetically costly 443 (Calvo, Wilson, Bok, & Keller, 2002), and may impose a fitness penalty if it reduces growth 444 (Choi & Goodwin, 2011;Krishnan et al, 2018).…”