''Hortaea werneckii'' is a species of

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom (biology), kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are est ...

in the family

Teratosphaeriaceae Teratosphaeriaceae is a family of fungi in the order Mycosphaerellales. History In 2007, this family was recognized as distinct from the genus ''Mycosphaerella'', where it had previously been located, based on phylogenies constructed with the ...

. It is a

black yeast Black yeasts, sometimes also black fungi, dematiaceous fungi, microcolonial fungi or meristematic fungi is a diverse group of slow-growing microfungi which reproduce mostly asexually ( fungi imperfecti). Only few genera reproduce by budding cells ...

that is investigated for its remarkable

halotolerance Halotolerance is the adaptation of living organisms to conditions of high salinity. Halotolerant species tend to live in areas such as hypersaline lakes, coastal dunes, saline deserts, salt marshes, and inland salt seas and springs. Halophiles ar ...

. While the addition of salt to the medium is not required for its cultivation, ''H. werneckii'' can grow in close to

saturated Saturation, saturated, unsaturation or unsaturated may refer to: Chemistry *Saturated and unsaturated compounds, a classification of compounds related to their ability to resist addition reactions **Degree of unsaturation **Saturated fat or satur ...

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". Several salt-tolerance mechanisms of ''H. werneckii ''have been studied on molecular level. For example, it is known that its major

compatible solutes Osmoprotectants or compatible solutes are small organic molecules with neutral charge and low toxicity at high concentrations that act as osmolytes and help organisms to survive in extreme osmotic stress. Osmoprotectants can be placed in three che ...

are

glycerol Glycerol () is a simple triol compound. It is a colorless, odorless, sweet-tasting, viscous liquid. The glycerol backbone is found in lipids known as glycerides. It is also widely used as a sweetener in the food industry and as a humectant in pha ...

erythritol Erythritol (, ) is an organic compound, the naturally occurring achiral meso four-carbon sugar alcohol (or polyol). It is the reduced form of either D- or L- erythrose and one of the two reduced forms of erythrulose. It is used as a food ad ...

arabitol Arabitol, or arabinitol, is a sugar alcohol. It can be formed by the reduction of either arabinose or lyxose. Some organic acid tests check for the presence of D-arabitol, which may indicate overgrowth of intestinal microbes such as '' Candida ...

, and

mannitol Mannitol is a type of sugar alcohol used as a sweetener and medication. It is used as a low calorie sweetener as it is poorly absorbed by the intestines. As a medication, it is used to decrease pressure in the eyes, as in glaucoma, and to l ...

;

melanin Melanin (; ) is a family of biomolecules organized as oligomers or polymers, which among other functions provide the pigments of many organisms. Melanin pigments are produced in a specialized group of cells known as melanocytes. There are ...

accumulation of the cell wall aids in retention of at least glycerol inside of the cell. Several components of the high osmolarity glycerol (HOG) signalling pathway (which controls responses to

osmotic shock Osmotic shock or osmotic stress is physiologic dysfunction caused by a sudden change in the solute concentration around a cell, which causes a rapid change in the movement of water across its cell membrane. Under hypertonic conditions - conditio ...

) have been studied in detail and some seem to differ in function compared to their counterparts in ''

Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungal microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have be ...

''. Adaptation to high concentrations of

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

are also accompanied by changes in membrane

lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...

composition, mainly by increasing the unsaturation of the phospholipid fatty acids. ''H. werneckii ''causes a rare superficial and non-invasive skin infection

tinea nigra Tinea nigra, also known as superficial phaeohyphomycosis and Tinea nigra palmaris et plantaris, is a superficial fungal infection, a type of phaeohyphomycosis rather than a tinea, that causes usually a single 1–5 cm dark brown-black, non- ...

. The typical symptoms are non-scaly, smooth, brown-black painless spots on the palms of hands and soles of feet. The growth of ''H. werneckii'' in liquid

media Media may refer to: Communication * Means of communication, tools and channels used to deliver information or data ** Advertising media, various media, content, buying and placement for advertising ** Interactive media, media that is inter ...

is often

-like, although it can switch to

filamentous The word filament, which is descended from Latin ''filum'' meaning "Thread (yarn), thread", is used in English for a variety of thread-like structures, including: Astronomy * Galaxy filament, the largest known cosmic structures in the universe * ...

growth. The mechanism of the switch is not known. The cells appear brown because of melanin production.

Whole genome sequencing Whole genome sequencing (WGS), also known as full genome sequencing or just genome sequencing, is the process of determining the entirety of the DNA sequence of an organism's genome at a single time. This entails sequencing all of an organism's ...

of ''H. werneckii'' revealed a recent

whole genome duplication Paleopolyploidy is the result of genome duplications which occurred at least several million years ago (MYA). Such an event could either double the genome of a single species ( autopolyploidy) or combine those of two species ( allopolyploidy). ...

, thought to be the only reported whole-genome duplication among ascomycetous yeasts besides the better known one in the ''

'' lineage. Based on genome sequencing of additional strains, 10 out of 12 strains have a genome that was duplicated by several hybridizations between haploid strains, yielding formed stable diploids. Apart from these hybridization events, no signs of sexual reproduction were found. As a consequence, the genome of ''H. werneckii'' is relatively large (49.9 Mb) with 15974 predicted genes. Genes encoding metal cation transporters, which are thought to play a role in

, experienced several additional

gene duplication Gene duplication (or chromosomal duplication or gene amplification) is a major mechanism through which new genetic material is generated during molecular evolution. It can be defined as any duplication of a region of DNA that contains a gene ...

s at various points during their evolution. A

homothallic In fungi and algae, homothallism refers to the condition in which a single individual or thallus carries the genetic determinants (i.e., both mating types or sexes) required to undergo sexual reproduction without the need for a distinct mating partn ...

mating locus was found in all sequenced genomes, although one of the mating genes may have been inactivated in some strains. Despite this, phylogenetic analyses and

linkage disequilibrium Linkage disequilibrium, often abbreviated to LD, is a term in population genetics referring to the association of genes, usually linked genes, in a population. It has become an important tool in medical genetics and other fields In defining LD, it ...

analyses indicate that ''H. werneckii'' is asexual.

References

{{Taxonbar, from=Q5906640 Capnodiales Fungus species Fungi described in 1984