''Hortaea werneckii'' is a species of

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

in the family

Teratosphaeriaceae Teratosphaeriaceae is a family of fungi in the order Capnodiales. 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 Large S ...

. 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 ...

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 are ...

. 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 * Saturation, a property of organic compounds referring to carbon-carbon bonds ** Saturated and unsaturated compounds **Degree of unsaturation ** Saturated fat or fatty ac ...

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 survive extreme osmotic stress. Osmoprotectants can be placed in three chemical ...

are

glycerol Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...

erythritol Erythritol is an organic compound, a four-carbon sugar alcohol (or polyol) with no optical activity, used as a food additive and sugar substitute. It is naturally occurring. It can be made from corn using enzymes and fermentation. Its formula is ...

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 a ...

, 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 lo ...

;

melanin Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...

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 - conditions ...

) 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 fungus microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have b ...

''. Adaptation to high concentrations of

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...

are also accompanied by changes in membrane

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids includ ...

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 * Media (communication), tools used to deliver information or data ** Advertising media, various media, content, buying and placement for advertising ** Broadcast media, communications delivered over mass e ...

is often

-like, although it can switch to filamentous 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, complete genome sequencing, or entire genome sequencing, is the process of determining the entirety, or nearly the entirety, of the DNA sequence of an organism's genome at a ...

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). Bec ...

, 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 duplications at various points during their evolution. A

homothallic Homothallic refers to the possession, within a single organism, of the resources to reproduce sexually; i.e., having male and female reproductive structures on the same thallus. The opposite sexual functions are performed by different cells of a si ...

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 In population genetics, linkage disequilibrium (LD) is the non-random association of alleles at different loci in a given population. Loci are said to be in linkage disequilibrium when the frequency of association of their different alleles is h ...

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

References

{{Taxonbar, from=Q5906640 Capnodiales