DOPA and DHN pathway orchestrate melanin synthesis inAspergillusspecies

Abstract

Melanins are high molecular weight hydrophobic pigments that have been studied for their role in the virulence of fungal pathogens. We investigated the amount and type of melanin in 20 isolates of Aspergillus spp.; A. niger (n = 3), A. flavus (n = 5), A. tamarii (n = 3), A. terreus (n = 3), A. tubingensis (n = 3), A. sydowii (n = 3). Aspergillus spp. were identified by sequencing the internal transcribed spacer (ITS) region. Extraction of melanin from culture filtrate and fungal biomass was done and followed by qualitative and quantitative analysis of melanin pigment. Ultraviolet (UV), Fourier transformed infrared (FT-IR), and electron paramagnetic resonance (EPR) spectra analyses confirmed the presence of melanin. The melanin pathway was studied by analyzing the effects of inhibitors; kojic acid, tropolone, phthalide, and tricyclazole. The results indicate that in A. niger and A. tubingensis melanin was found in both culture filtrate and fungal biomass. For A. tamarii and A. flavus melanin was extracted from biomass only, whereas melanin was found only in culture filtrate for A. terreus. A negligible amount of melanin was found in A. sydowii. The maximum amount of melanin from culture filtrate and fungal biomass was found in A. niger and A. tamarrii, respectively. The DOPA (3,4-dihydroxyphenylalanine) pathway produces melanin in A. niger, A. tamarii and A. flavus, whereas the DHN (1,8-dihydroxynaphthalene) pathway produces melanin in A. tubingensis and A. terreus. It can be concluded that the amount and type of melanin in aspergilli largely differ from species to species.

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

“…Melanins are most stable, amorphous polymers of phenolic compounds and can be classified into the following three types: eumelanins, pheomelanins and allomelanins. Melanin production helps in protection from extreme environmental conditions such as UV light, ionising radiation, resistance to heat or cold, phagocytosis, heavy metals, and oxidants and provides cell wall rigidity (Money et al 1998; Plonka and Grabacka 2006; Pal et al 2013; Casadevall et al 2017). Despite its importance and ubiquity, many fundamental questions remain unanswered like details of its chemical structure and insolubility (Eisenman and Casadevall 2012).…”

“…tritici, Magnaporthe grisea, Alternaria alternata, Colletotrichum lagenarium, Cochliobolus heterostrophus (Henson et al 1999), Paecilomyces variotti (Babitskaya et al 2000a), Rhizoctonia solani (Chen et al 2015) and Aspergillus spp. (Babitskaya et al 2000a; Schmaler-Ripcke et al 2009; Gonçalves et al 2012; Pal et al 2013). Melanins are reported from mushrooms such as Agaricus bisporus (Mendoza et al 1979), Inonotus obliquus (Babitskaia et al 2000b; Babitskaya et al 2002), and Schizophyllum commune (Arun et al 2015).…”

SOME NATURAL AND SYNTHETIC COMPOUNDS INHIBITING THE BIOSYNTHESIS OF AFLATOXIN B1 AND MELANIN IN Aspergillus flavus

“…Melanins of indole or pentaketid nature protect fungi against damaging biotic or abiotic factors [7][8][9]. In the genus Aspergillus, melanins, which represent hydrophobic macromolecular pigments, may be synthesized via two pathways depending on the fungus species; the first one is the indole pathway via DOPA (3,4-dihydroxy-phenylalanine), and the second one is the pentaketide pathway via DHN (1,8-dihydroxy-naphthalene) [10]. Melanins are required for the survival and virulence of many pathogens [11,12].…”

Effect of Various Compounds Blocking the Colony Pigmentation on the Aflatoxin B1 Production by Aspergillus flavus

“…Fungal melanins, representing high-molecular hydrophobic pigments, are also synthesized via the PKS-depending pathway [6]. The blocking of the melanin biosynthesis in pathogenic fungi can result in the loss of their pathogenicity and an increased susceptibility of fungi to biotic and abiotic stresses [7,8,9].…”