Characterization of a novel polyextremotolerant fungus, Exophiala viscosa, with insights into its melanin regulation and ecological niche

Abstract

Black yeasts are polyextremotolerant fungi that contain high amounts of melanin in their cell wall and maintain a primar yeast form. These fungi grow in xeric, nutrient depletes environments which implies that they require highly flexible metabolisms and have been suggested to contain the ability to form lichen-like mutualisms with nearby algae and bacteria. However, the exact ecological niche and interactions between these fungi and their surrounding community are not well understood. We have isolated 2 novel black yeasts from the genus Exophiala that were recovered from dryland biological soil crusts. Despite notable differences in colony and cellular morphology, both fungi appear to be members of the same species, which has been named Exophiala viscosa (i.e. E. viscosa JF 03-3 Goopy and E. viscosa JF 03-4F Slimy). A combination of whole genome sequencing, phenotypic experiments, and melanin regulation experiments have been performed on these isolates to fully characterize these fungi and help decipher their fundamental niche within the biological soil crust consortium. Our results reveal that E. viscosa is capable of utilizing a wide variety of carbon and nitrogen sources potentially derived from symbiotic microbes, can withstand many forms of abiotic stresses, and excretes melanin which can potentially provide ultraviolet resistance to the biological soil crust community. Besides the identification of a novel species within the genus Exophiala, our study also provides new insight into the regulation of melanin production in polyextremotolerant fungi.

Non-photochemical quenching may contribute to the dominance of the pale mat-forming lichen Cladonia stellaris over the sympatric melanic Cetraria islandica

“…The high light compensation in Cetraria was shaped by high dark respiration, which seasonally acclimates (Lange and Green 2005 ). The higher dark respiration in spring than in summer of Cetraria indicates that its dark respiration has a higher acclimation potential than of Cladonia , consistent with the view that melanic fungi are considered extremotolerant (Carr et al 2023 ). Dark respiration was probably acclimated to low temperature after vernal snowmelt and later reduced in summer.…”

Exophiala amphawaensis sp. nov., a novel black yeast isolated from the gut of amphipods in Thailand

“…In the MycoBank database (https://www.mycobank.org/; December 2023), 70 species of the genus Exophiala have been recognised. Later, some species of the genus Exophiala were reassigned to the other genera like Hortaea and Neophaeococcomyces [9, 10] , while a few novel species have been described as members of the genus Exophiala [11–13].…”

Exophiala chapopotensis sp. nov., an extremotolerant black yeast from an oil-polluted soil in Mexico; phylophenetic approach to species hypothesis in the Herpotrichiellaceae family

“…The data corresponding to the strains compared in this table were extracted from the available literature[10,54,[56][57][58][59][60][61][62][63][64][65][66][67][68][69]. + = good growth;-= no growth; d = poor growth; v = variable; ND: ambiguous or unknown; PNPG = β-galactosidase (Para-NitroPhenyl-ßDGalactopyranosidase).…”