Phenotypic Characterization and Comparative Genomics of the Melanin-Producing Yeast Exophiala lecanii-corni Reveals a Distinct Stress Tolerance Profile and Reduced Ribosomal Genetic Content

Abstract

The black yeast Exophiala lecanii-corni of the order Chaetothyriales is notable for its ability to produce abundant quantities of DHN-melanin. While many other Exophiala species are frequent causal agents of human infection, E. lecanii-corni CBS 102400 lacks the thermotolerance requirements that enable pathogenicity, making it appealing for use in targeted functional studies and biotechnological applications. Here, we report the stress tolerance characteristics of E. lecanii-corni, with an emphasis on the influence of melanin on its resistance to various forms of stress. We find that E. lecanii-corni has a distinct stress tolerance profile that includes variation in resistance to temperature, osmotic, and oxidative stress relative to the extremophilic and pathogenic black yeast Exophiala dermatitidis. Notably, the presence of melanin substantially impacts stress resistance in E. lecanii-corni, while this was not found to be the case in E. dermatitidis. The cellular context, therefore, influences the role of melanin in stress protection. In addition, we present a detailed analysis of the E. lecanii-corni genome, revealing key differences in functional genetic content relative to other ascomycetous species, including a significant decrease in abundance of genes encoding ribosomal proteins. In all, this study provides insight into how genetics and physiology may underlie stress tolerance and enhances understanding of the genetic diversity of black yeasts.

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

“…Either this excreted melanin is an evolutionary trait that is beneficial to the fungi in some way, or this melanin excretion is a form of overflow metabolism in which melanin is the most streamlined way to remove an excessive buildup of precursors ( De Deken 1966 ). Additionally, there are not many fungi known to excrete melanin, and few in the genus Exophiala ( Romsdahl et al 2021 ), so the possibility of a novel species that excrete such extreme amounts of melanin into their surroundings was intriguing.…”

Core Microbiome and Microbial Community Structure in Coralloid Roots of Cycas in Ex Situ Collection of Kunming Botanical Garden in China

“…The abundance of Exophiala from the biological soil crusts was found to have a positive correlation with microbial biomass nitrogen (MBN), electrolytic conductivity (EC), nitrate (NO 3 − ), suggesting its potential for nitrogen fixation [ 76 ]. Additionally, Exophiala has demonstrated the ability to resist various forms of stress [ 77 ], improve plant tolerance to adverse environment and promote host plant growth [ 78 , 79 ]. Meanwhile, according to our results, Nectriaceae had also been shown to be a core fungal family in coralloid roots of all Cycas sections, suggesting a universality of the family in Cycas .…”

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

“…Either this excreted melanin is an evolutionary trait that is beneficial to the fungi in some way, or this melanin excretion is a form of overflow metabolism in which melanin is the most streamlined way to remove an excessive buildup of precursors (De Deken, 1966). Additionally, there are not many fungi known to excrete melanin and few in the genus Exophiala (Romsdahl et al, 2021), so the possibility of a novel species that excretes such extreme amounts of melanin into their surroundings was intriguing.…”