Melanin is crucial for growth of the black yeast Hortaea werneckii in its natural hypersaline environment

• Published in: Fungal biology 2013-05, Vol.117 (5), p.368-379
• Main Authors: Kejžar, Anja, Gobec, Stanislav, Plemenitaš, Ana, Lenassi, Metka
• Format: Article
• Language: English
• Subjects: Ascomycota - genetics; Ascomycota - growth & development; Ascomycota - metabolism; biosynthesis; Black yeast; cell division; Cell wall; cell walls; color; Fungal Proteins - genetics; Fungal Proteins - metabolism; Gene Expression Regulation, Fungal; glycerol; Hortaea werneckii; hydrogen peroxide; Melanin; Melanins - metabolism; NaCl; Oxidative Stress; pigmentation; salinity; sodium chloride; Sodium Chloride - metabolism; Stress; Tricyclazole; yeasts
• ISSN: 1878-6146; 1878-6162
• DOI: 10.1016/j.funbio.2013.03.006

Melanin has an important role in the ability of fungi to survive extreme conditions, like the high NaCl concentrations that are typical of hypersaline environments. The black fungus Hortaea werneckii that has been isolated from such environments has 1,8-dihydroxynaphthalene-melanin incorporated into the cell wall, which minimises the loss of glycerol at low NaCl concentrations. To further explore the role of melanin in the extremely halotolerant character of H. werneckii, we studied the effects of several melanin biosynthesis inhibitors on its growth, pigmentation and cell morphology. The most potent inhibitors were a 2,3-dihydrobenzofuran derivative and tricyclazole, which restricted the growth of H. werneckii on high-salinity media, as shown by growth curves and plate-drop assays. These inhibitors promoted release of the pigments from the H. werneckii cell surface and changed the medium colour. Inhibitor-treated H. werneckii cells exposed to high salinity showed both decreased and increased cell lengths. We speculate that this absence of melanin perturbs the integrity of the cell wall in H. werneckii, which affects its cell division and exposes it to the harmful effects of high NaCl concentrations. Surprisingly, melanin had no effect on H. werneckii survival under H2O2 oxidative stress. •Inhibitors of melanin biosynthesis release pigments from H. werneckii cell surface.•Absence of melanin restricts growth of H. werneckii in high sodium concentrations.•Absence of melanin affects cell morphology by perturbing cell-wall integrity.•Melanin has no role in H. werneckii survival under oxidative stress by H2O2.•Melanin is crucial for the extreme halotolerant character of H. werneckii.