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''Cryptococcus'' is a
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of fungi in the
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
Cryptococcaceae that includes both
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 ...
s and filamentous
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
. The filamentous, sexual forms or teleomorphs were formerly classified in the genus ''Filobasidiella'', while ''Cryptococcus'' was reserved for the yeasts. Most yeast species formerly referred to ''Cryptococcus'' have now been placed in different genera. Some ''Cryptococcus'' species cause a disease called cryptococcosis.


Taxonomy

The genus was described by French mycologist Jean Paul Vuillemin in 1901, when he failed to find
ascospore In fungi, an ascospore is the sexual spore formed inside an ascus—the sac-like cell that defines the division Ascomycota, the largest and most diverse Division (botany), division of fungi. After two parental cell nucleus, nuclei fuse, the ascu ...
s characteristic of the genus '' Saccharomyces'' in the yeast previously known as ''Saccharomyces neoformans''. Over 300 additional names were subsequently added to the genus, almost all of which were later removed following molecular research based on
cladistic Cladistics ( ; from Ancient Greek 'branch') is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is ...
analysis of
DNA sequences A nucleic acid sequence is a succession of bases within the nucleotides forming alleles within a DNA (using GACT) or RNA (GACU) molecule. This succession is denoted by a series of a set of five different letters that indicate the order of the ...
. As a result, some ten species are currently recognized in ''Cryptococcus''. The teleomorph was first described in 1975 by K.J. Kwon-Chung, who obtained cultures of the
type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
, ''Filobasidiella neoformans'', by crossing strains of the yeast '' Cryptococcus neoformans''. She was able to observe basidia similar to those of the genus '' Filobasidium'', hence the name ''Filobasidiella'' for the new genus. Following changes to the
International Code of Nomenclature for algae, fungi, and plants The ''International Code of Nomenclature for algae, fungi, and plants'' (ICN or ICNafp) is the set of rules and recommendations dealing with the formal botanical names that are given to plants, fungi and a few other groups of organisms, all tho ...
, the practice of giving different names to teleomorph and anamorph forms of the same fungus was discontinued, meaning that ''Filobasidiella'' became a synonym of the earlier name ''Cryptococcus''.


General characteristics

The cells of species that produce yeasts are covered in a thin layer of glycoprotein capsular material that has a gelatin-like consistency, and that among other functions, serves to help extract nutrients from the soil. The ''C. neoformans'' capsule consists of several polysaccharides, of which the major one is the immunomodulatory polysaccharide called glucuronoxylomannan (GXM). GXM is made up of the monosaccharides
glucuronic acid Glucuronic acid (GCA, from ) is a uronic acid that was first isolated from urine (hence the name "uronic acid"). It is found in many natural gum, gums such as gum arabic ( 18%), xanthan, and kombucha tea and is important for the metabolism of ...
, xylose and mannose and can also contain O-acetyl groups. The capsule functions as the major virulence factor in cryptococcal infection and disease. Some ''Cryptococcus'' species have a huge diversity at the infraspecific level with different molecular types based on their genetic differences, mainly due to their geographical distribution, molecular characteristics, and ecological niches. ''Cryptococcus'' species are not known to produce distinct, visible fruitbodies. All teleomorph forms appear to be parasites of other fungi. In teleomorphs the
hyphae A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one o ...
are colourless, are clamped or unclamped, and bear haustorial cells with filaments that attach to the hyphae of host fungi. The basidia are club-shaped and highly elongated. Spores arise in succession from four loci at the apex (which is sometimes partly septate). These spores are passively released and may remain on the basidium in chains, unless disturbed. In the type species, the spores germinate to form yeast cells, but yeast states are not known for all species.


Habitat, distribution and species

''Cryptococcus neoformans'' is cosmopolitan and is the most prominent medically important species. It is best known for causing a severe form of
meningitis Meningitis is acute or chronic inflammation of the protective membranes covering the brain and spinal cord, collectively called the meninges. The most common symptoms are fever, intense headache, vomiting and neck stiffness and occasion ...
and meningoencephalitis in people with HIV/
AIDS The HIV, human immunodeficiency virus (HIV) is a retrovirus that attacks the immune system. Without treatment, it can lead to a spectrum of conditions including acquired immunodeficiency syndrome (AIDS). It is a Preventive healthcare, pr ...
. It may also infect organ-transplant recipients and people receiving certain cancer treatments. In its yeast state ''C. neoformans'' is found in the droppings of wild birds, often pigeons; when dust of the droppings is stirred up, it can infect humans or pets that inhale the dust. Infected humans and animals do not transmit their infection to others. The taxonomy of ''C. neoformans'' has been reviewed: it has now been divided into two species: ''Cryptococcus neoformans'' sensu stricto and ''Cryptococcus deneoformans''. ''Cryptococcus gattii'' (formerly ''C. neoformans'' var. ''gattii'') is endemic to tropical parts of the continent of Africa and Australia. It is capable of causing disease in non-immunocompromised people. In its yeast state it has been isolated from
eucalyptus ''Eucalyptus'' () is a genus of more than 700 species of flowering plants in the family Myrtaceae. Most species of ''Eucalyptus'' are trees, often Mallee (habit), mallees, and a few are shrubs. Along with several other genera in the tribe Eucalyp ...
trees in Australia. The taxonomy of ''C. gattii'' has been reviewed; it has now been divided into five species: ''C. gattii'' sensu stricto, ''C. bacillisporus'', ''C. deuterogattii'', ''C. tetragattii'', and ''C. decagattii''. '' Cryptococcus depauperatus'' is parasitic on '' Lecanicillium lecanii'', an entomopathogenic fungus, and is known from Sri Lanka, England, the Netherlands, the Czech Republic, and Canada. It is not known to produce a yeast state. This species grows as long, branching filaments and is self-fertile, i.e. it is homothallic. It can reproduce sexually with itself throughout its life cycle. '' Cryptococcus luteus'' is parasitic on '' Granulobasidium vellereum'', a corticioid fungus, and is known from England and Italy. It too is not known to produce a yeast state. '' Cryptococcus amylolentus'' was originally isolated as a yeast from beetle tunnels in South African trees. It forms a basidia-bearing teleomorph in culture. ,
Species Fungorum ''Index Fungorum'' is an international project to index all formal names (Binomial nomenclature, scientific names) in the fungus Kingdom (biology), kingdom. As of 2015, the project is based at the Royal Botanic Gardens, Kew, one of three partn ...
(in the
Catalogue of Life The Catalogue of Life (CoL) is an online database that provides an index of known species of animals, plants, fungi, and microorganisms. It was created in 2001 as a partnership between the global Species 2000 and the American Integrated Taxono ...
) accept 41 species of ''Cryptococcus'': * '' Cryptococcus amylolentus'' * '' Cryptococcus asgardensis'' * '' Cryptococcus aureus'' * '' Cryptococcus bacillisporus'' * '' Cryptococcus baldrensis'' * '' Cryptococcus cavarae'' * '' Cryptococcus cellulolyticus'' * '' Cryptococcus cereanus'' * '' Cryptococcus consortionis'' * '' Cryptococcus decagattii'' * '' Cryptococcus deneoformans'' * '' Cryptococcus depauperatus'' * '' Cryptococcus deuterogattii'' * '' Cryptococcus elinovii'' * '' Cryptococcus ferigula'' * '' Cryptococcus festucosus'' * '' Cryptococcus floricola'' * '' Cryptococcus gattii'' * '' Cryptococcus hempflingii'' * '' Cryptococcus heveanensis'' * '' Cryptococcus himalayensis'' * '' Cryptococcus hominis'' * '' Cryptococcus lactativorus'' * '' Cryptococcus longus'' * '' Cryptococcus lupi'' * '' Cryptococcus luteus'' * '' Cryptococcus montanae'' * '' Cryptococcus musci'' * '' Cryptococcus mycelialis'' * '' Cryptococcus neoformans'' * '' Cryptococcus nyarrowii'' * '' Cryptococcus pseudolongus'' * '' Cryptococcus ramirezgomezianus'' * '' Cryptococcus saitoi'' * '' Cryptococcus socialis'' * '' Cryptococcus tetragattii'' * '' Cryptococcus tyrolensis'' * '' Cryptococcus uniguttulatus'' * '' Cryptococcus watticus'' * '' Cryptococcus wingfieldii '' * '' Cryptococcus wrightensis''


References

{{Authority control Tremellomycetes Basidiomycota genera Yeasts