Malassezia

''Malassezia'' (formerly known as ''Pityrosporum'') is a genus of fungi. It is the sole genus in family Malasseziaceae, which is the only family in order Malasseziales, itself the single member of class Malasseziomycetes. ''Malassezia'' species are naturally found on the skin surfaces of many animals, including humans. In occasional opportunistic infections, some species can cause hypopigmentation or hyperpigmentation on the trunk and other locations in humans. Allergy tests for these fungi are available.

Systematics

Due to progressive changes in their nomenclature, some confusion exists about the naming and classification of ''Malassezia'' yeast species. Work on these yeasts has been complicated because they require specific growth media and grow very slowly in laboratory culture.

''Malassezia'' were originally identified by the French scientist Louis-Charles Malassez in the late nineteenth century. Raymond Sabouraud identified a dandruff-causing organism in 1904 and called it "Pityrosporum malassez", honoring Malassez, but at the species level as opposed to the genus level. When it was determined that the organisms were the same, the term "Malassezia" was judged to possess priority.

In the mid-twentieth century, it was reclassified into two species:
* ''Pityrosporum (Malassezia) ovale'', which is lipid-dependent and found only on humans. ''P. ovale'' was later divided into two species, ''P. ovale'' and ''P. orbiculare'', but current sources consider these terms to refer to a single species of fungus, with ''M. furfur'' the preferred name.
* ''Pityrosporum (Malassezia) pachydermatis'', which is lipophilic but not lipid-dependent. It is found on the skin of most animals.
In the mid-1990s, scientists at the Pasteur Institute in Paris, France, discovered additional species.

''Malassezia'' is the sole genus in the family Malasseziaceae, which was validated by Cvetomir Denchev and Royall T. Moore in 2009. The order Malasseziales had been previously proposed by Moore in 1980, and later emended by Begerow and colleagues in 2000. At this time the order was classified as a member of unknown class placement in the subdivision Ustilaginomycotina. In 2014, Cvetomir and Teodor Denchev circumscribed the class Malasseziomycetes to contain the group.

Species

Species Fungorum accepts 22 species of ''Malassezia''. The following list gives the name of the fungus, the taxonomic authority (those who first described the fungus, or who transferred it into ''Malassezia'' from another genus; standardized author abbreviations are used), and the name of the organism from which the fungus was isolated, if not human.

*''Malassezia arunalokei''
*''Malassezia brasiliensis'' – from lesions on the beak of turquoise-fronted amazon parrot
*''Malassezia caprae'' – from skin of goat
*''Malassezia cuniculi'' – from healthy skin of external ear canal of rabbit
*''Malassezia dermatis''
*'' Malassezia equi'' – from skin of horse
*''Malassezia equina'' – from skin of horse
*''Malassezia furfur''
*'' Malassezia globosa''
*''Malassezia japonica''
*''Malassezia muris'' – skin of mouse
*''Malassezia nana'' – from discharge from ear of cat
*''Malassezia obtusa''
*''Malassezia ochoterenai''
*'' Malassezia pachydermatis'' – from skin of Indian rhinoceros
*'' Malassezia psittaci'' – from lesions on the beak of blue-headed parrot
*'' Malassezia restricta''
*'' Malassezia slooffiae'' – from skin of pig
*''Malassezia sympodialis''
*'' Malassezia tropica''
*'' Malassezia vespertilionis'' – from vesper bats in subfamily Myotinae
*'' Malassezia yamatoensis''

Role in human diseases

Dermatitis and dandruff

Identification of ''Malassezia'' on skin has been aided by the application of molecular or DNA-based techniques. These investigations show that the ''Malassezia'' species causing most skin disease in humans, including the most common cause of dandruff and seborrhoeic dermatitis, is ''M. globosa'' (though ''M. restricta'' is also involved). The skin rash of tinea versicolor (''pityriasis versicolor'') is also due to infection by this fungus.

As the fungus requires fat to grow, it is most common in areas with many sebaceous glands: on the scalp, face, and upper part of the body. When the fungus grows too rapidly, the natural renewal of cells is disturbed, and dandruff appears with itching (a similar process may also occur with other fungi or bacteria).

A project in 2007 has sequenced the genome of dandruff-causing ''Malassezia globosa'' and found it to have 4,285 genes. ''M. globosa'' uses eight different types of lipase, along with three phospholipases, to break down the oils on the scalp. Any of these 11 proteins would be a suitable target for dandruff medications.

The number of specimens of ''M. globosa'' on a human head can be up to ten million.

''M. globosa'' has been predicted to have the ability to reproduce sexually, but this has not been observed.

Research

''Malassezia'' is among the many mycobiota undergoing laboratory research to investigate whether it is associated with types of disease.

References

Further reading

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{{Taxonbar, from=Q14488912

Basidiomycota
Parasitic fungi
Yeasts
Taxa described in 1889
Taxa named by Henri Ernest Baillon