Black yeasts, sometimes also black fungi, dematiaceous fungi, microcolonial fungi or meristematic fungi [1] is a diverse group of slow-growing microfungi which reproduce mostly asexually (fungi imperfecti). Only few genera reproduce by budding cells, while in others hyphal or meristematic (isodiametric) reproduction is preponderant. [2] [3] [4] [5] Black yeasts share some distinctive characteristics, in particular a dark colouration (melanisation) of their cell wall. Morphological plasticity, incrustation of the cell wall with melanins and presence of other protective substances like carotenoids and mycosporines [6] represent passive physiological adaptations which enable black fungi to be highly resistant against environmental stresses. [7] The term "polyextremotolerance" has been introduced to describe this phenotype, an example of which is the species Aureobasidium pullulans . [8] Presence of 1,8-dihydroxynaphthalene melanin in the cell wall [9] confers to the microfungi their characteristic olivaceous to dark brown/black colour.
The consortium comprises two phylogenetically very different fungal groups. [10] [11] Many are found in the orders Capnodiales, Dothideales, and Pleosporales (class Dothideomycetes). These black fungi mostly have an extremotolerant life style. Many representatives of this group can colonize bare rocks, e.g. in the Mediterranean basin or in hot and cold dry deserts, and are therefore referred to as rock-inhabiting fungi, [10] [11] or occur in salterns. [12] These black yeasts are believed to be the most resistant eukaryotic organisms known to-date. [7] They were firstly described in the early 80s by three almost concomitant seminal research articles. [13] [14] [15] Members of Chaetothyriales (class Eurotiomycetes) [10] [11] are found in hydrocarbon-rich environments or in nutrient-poor, moist indoor environments, and may occur as opportunistic pathogens of vertebrate hosts, such as Exophiala (Wangiella) dermatitidis. [16] Several species are associated with lichens [17] [18] as well as other phototrophs [19] and sometimes with ants in specific ant-fungi associations. [20]
In recent years, black fungi such as E. dermatitidis or Hortaea werneckii have attracted increasingly attention as model microorganisms in studies on astrobiology, [21] bioremediation of polluted ecosystems by biofiltration, [22] effect of ionizing radiations in contaminated area, [23] [24] biodeterioration of materials, [25] [26] and mechanisms of adaptation to high salt concentrations. [12] A collaborative effort coordinated by the Broad Institute is currently ongoing to sequence the genomes of several black fungi to shed light into their ecology, phylogeny and pathogenicity.
In 2011, a research paper about occurrence of potentially pathogenic black fungi in household dishwashers [27] was partially misreported by the media and went viral.[ citation needed ]
Black yeasts are not related to the edible cloud ear fungus Auricularia polytricha. [10] [11]
Dothideomycetes is the largest and most diverse class of ascomycete fungi. It comprises 11 orders 90 families, 1,300 genera and over 19,000 known species. Wijayawardene et al. in 2020 added more orders to the class.
Aureobasidium pullulans is a ubiquitous and generalistic black, yeast-like fungus that can be found in different environments. It is well known as a naturally occurring epiphyte or endophyte of a wide range of plant species without causing any symptoms of disease. A. pullulans has a high importance in biotechnology for the production of different enzymes, siderophores and pullulan. Furthermore, A. pullulans is used in biological control of plant diseases, especially storage diseases.
Exophiala jeanselmei is a saprotrophic fungus in the family Herpotrichiellaceae. Four varieties have been discovered: Exophiala jeanselmei var. heteromorpha, E. jeanselmei var. lecanii-corni, E. jeanselmei var. jeanselmei, and E. jeanselmei var. castellanii. Other species in the genus Exophiala such as E. dermatitidis and E. spinifera have been reported to have similar annellidic conidiogenesis and may therefore be difficult to differentiate.
The Pleosporales is the largest order in the fungal class Dothideomycetes. By a 2008 estimate, it contained 23 families, 332 genera and more than 4700 species. The majority of species are saprobes on decaying plant material in fresh water, marine, or terrestrial environments, but several species are also associated with living plants as parasites, epiphytes or endophytes. The best studied species cause plant diseases on important agricultural crops e.g. Cochliobolus heterostrophus, causing southern corn leaf blight on maize, Phaeosphaeria nodorum causing glume blotch on wheat and Leptosphaeria maculans causing a stem canker on cabbage crops (Brassica). Some species of Pleosporales occur on animal dung, and a small number occur as lichens and rock-inhabiting fungi.
Hortaea werneckii is a species of yeast in the family Teratosphaeriaceae. It is a black yeast that is investigated for its remarkable halotolerance. While the addition of salt to the medium is not required for its cultivation, H. werneckii can grow in close to saturated NaCl solutions. To emphasize this unusually wide adaptability, and to distinguish H. werneckii from other halotolerant fungi, which have lower maximum salinity limits, some authors describe H. werneckii as "extremely halotolerant".
Moniliella is a genus of fungi in the subdivision Ustilaginomycotina. It is in the monotypic family MoniliellaceaeQ.M. Wang, F.Y. Bai & Boekhout, which is in the monotypic order MoniliellalesQ.M. Wang, F.Y. Bai & Boekhout which is in the monotypic class MoniliellomycetesQ.M. Wang, F.Y. Bai & Boekhout.
The Wallemiomycetes are a class of fungi in the division Basidiomycota. It consists of the single order Wallemiales, containing the single family Wallemiaceae, which in turn contains the single genus Wallemia. The phylogenetic origin of the lineage was placed to various parts of Basidiomycota, but according to the analysis of a larger dataset it is a sister group of Agaricomycotina. The genus contains species of xerophilic molds that are found worldwide. The seven described species are distinguished by conidial size, xerotolerance, halotolerance, chaotolerance, growth temperature regimes, extracellular enzyme activity profiles, and secondary metabolite patterns. They are typically isolated from low-moisture foods, indoor air dust, salterns and soil. W. sebi is thought to be one of the causes of the hypersensitivity pneumonitis known as the farmer's lung disease, but since the other species were recognised and separated from W. sebi only recently, their role in the disease cannot be excluded.
Exophiala dermatitidis is a thermophilic black yeast, and a member of the Herpotrichiellaceae. While the species is only found at low abundance in nature, metabolically active strains are commonly isolated in saunas, steam baths, and dish washers. Exophiala dermatitidis only rarely causes infection in humans, however cases have been reported around the world. In East Asia, the species has caused lethal brain infections in young and otherwise healthy individuals. The fungus has been known to cause cutaneous and subcutaneous phaeohyphomycosis, and as a lung colonist in people with cystic fibrosis in Europe. In 2002, an outbreak of systemic E. dermatitidis infection occurred in women who had received contaminated steroid injections at North Carolina hospitals.
Cladosporium dominicanum is a fungus found in hypersaline environments. It has globoid conidia. It has also been found in plant material.
Cladosporium halotolerans is a fungus found in hypersaline environments. It has globoid conidia. It has also been isolated from bathrooms and in a dolphin.
Cladosporium fusiforme is a fungus found in hypersaline environments. It has ovoid to ellipsoid conidia. It has also been found in animal feed.
Wallemia ichthyophaga is one of the three species of fungi in the genus Wallemia, which in turn is the only genus of the class Wallemiomycetes. The phylogenetic origin of the lineage was placed to various parts of Basidiomycota, but according to the analysis of larger datasets it is a (495-million-years-old) sister group of Agaricomycotina. Although initially believed to be asexual, population genomics found evidence of recombination between strains and a mating type locus was identified in all sequenced genomes of the species.
Previously classified under the species complex Aureobasidium pullulans, Aureobasidium subglaciale is a black yeast-like, extremophile, ascomycete fungus that is found in extreme cold habitats. The species was originally isolated from subglacial ice of arctic glaciers. The first isolate of this species was obtained from subglacial ice of the Norwegian island Spitsbergen, one of the coldest places inhabited by humans. of Genomic data collected from specimens in the Aureobasidium pullulans complex justified distinction of four different species
Teratosphaeriaceae is a family of fungi in the order Mycosphaerellales.
Aureobasidium melanogenum, formerly known as Aureobasidium pullulans var. melanogenum is a ubiquitous black, yeast-like fungus that is found mainly in freshwater habitats. The species also includes strains causing human infections, which were previously classified as A. pullulans. It was named due to abundant melanin production and accumulation in the cell walls, which leads to dark green, brown or black appearance of the cells and colonies The species was established when the genomes of the four former varieties of Aureobasidium pullulans were sequenced and the large differences between them were discovered.
Aureobasidium namibiae, formerly known as Aureobasidium pullulans var. namibiae is a ubiquitous black, yeast-like fungus. It was described on the basis of only one strain isolated from dolomitic marble in Namibia. The species was established when the genomes of the four former varieties of Aureobasidium pullulans were sequenced and the large differences between them were discovered.
Exophiala phaeomuriformis is thermophilic fungus belonging to the genus Exophiala and the family Herpotrichiellaceae. it is a member of the group of fungi known as black yeasts, and is typically found in hot and humid locations, such as saunas, bathrooms, and dishwashers. This species can cause skin infections and is typically classified as a Biosafety Risk Group 2 agent.
Cladophialophora carrionii is a melanized fungus in the genus Cladophialophora that is associated with decaying plant material like cacti and wood. It is one of the most frequent species of Cladophialophora implicated in human disease. Cladophialophora carrionii is a causative agent of chromoblastomycosis, a subcutaneous infection that occurs in sub-tropical areas such as Madagascar, Australia and northwestern Venezuela. Transmission occurs through traumatic implantation of plant material colonized by C. carrionii, mainly infecting rural workers. When C. carrionii infects its host, it transforms from a mycelial state to a muriform state to better tolerate the extreme conditions in the host's body.
Cladosporium sphaerospermum is a radiotrophic fungus belonging to the genus Cladosporium and was described in 1886 by Albert Julius Otto Penzig from the decaying leaves and branches of Citrus. It is a dematiaceous (darkly-pigmented) fungus characterized by slow growth and largely asexual reproduction. Cladosporium sphaerospermum consists of a complex of poorly morphologically differentiated, "cryptic" species that share many physiological and ecological attributes. In older literature, all of these sibling species were classified as C. sphaerospermum despite their unique nature. Accordingly, there is confusion in older literature reports on the physiological and habitat regularities of C. sphaerospermum in the strict sense. This fungus is most phylogenetically similar to C. fusiforme. According to modern phylogenetic analyses, the previously synonymized species, Cladosporium langeroni, is a distinct species.
Fungal genomes are among the smallest genomes of eukaryotes. The sizes of fungal genomes range from less than 10 Mbp to hundreds of Mbp. The average genome size is approximately 37 Mbp in Ascomycota, 47 Mbp in Basidiomycota and 75 Mbp in Oomycota. The sizes and gene numbers of the smallest genomes of free-living fungi such as those of Wallemia ichthyophaga, Wallemia mellicola or Malassezia restricta are comparable to bacterial genomes. The genome of the extensively researched yeast Saccharomyces cerevisiae contains approximately 12 Mbp and was the first completely sequenced eukaryotic genome. Due to their compact size fungal genomes can be sequenced with less resources than most other eukaryotic genomes and are thus important models for research. Some fungi exist as stable haploid, diploid, or polyploid cells, others change ploidy in response to environmental conditions and aneuploidy is also observed in novel environments or during periods of stress.