Geotrichum candidum

Geotrichum candidum is a fungus which is a member of the human microbiome, notably associated with skin, sputum, and faeces where it occurs in 25–30% of specimens. It is common in soil and has been isolated from soil collected around the world, in all continents.

G. candidum is the causative agent of the human disease geotrichosis and the plant disease sour rot which infects citrus fruits, tomatoes, carrots, and other vegetables. It can affect harvested fruit of durians such as Durio graveolens.

G. candidum is used widely in the production of certain dairy products including rind cheeses such as Camembert, Saint-Nectaire, Reblochon, and others. The fungus can also be found in a Nordic yogurt-like product known as viili where it is responsible for the product's velvety texture.

In a 2001 study, G. candidum was found to consume the polycarbonate found in CDs.

The genus Geotrichum was described by Johann Heinrich Friedrich Link in 1809 to accommodate the species G. candidum found on decaying leaves. Since then, over 130 taxa have been described in the genus, and hundreds of synonyms have been generated. For example, G. candidum was misclassified as the Oidium lactis in much early literature. Species of Geotrichum resemble the genera Trichosporon and Protendomycopsis; however, Geotrichum is of ascomycetous affiliation whereas the latter are members of the Basidiomycota. Species of Geotrichum are occasionally mistaken for fast growing members of the genus Dipodascus, which are characterized by irregularly branched, 10–14 μm wide hyphae and the production of single-spored asci. However, unlike Geotrichum, members of the genus Dipodascus lack dichotomous branching of the peripheral hyphae and their growth rates are generally less than 3 mm per day.

Galactomyces candidus, formerly thought to be a distinct taxon, was found to be the sexual state of G. candidum using sequence-based methods Geotrichum candidum in the broad sense comprises 3 clades, corresponding to the species G. candidum, G. clavatum and G. fici, all of which are thought to have pathogenic potential. Species of Geotrichum can be differentiated by sequence analysis of the nuclear ribosomal large subunit (18S ribosomal RNA) or the internal transcribed spacer region of the nuclear ribosomal RNA gene.

G. candidum colonies are thin, spreading, soft, creamy and white in the anamorph state. The fungus G. candidum is characterized by hyphae that appear creeping, mostly submerged and septate. The hyphae colour appears to be hyaline or lightly pigmented. When the hyphae becomes airborne it changes shape from arthroconidia to cylindrical or barrel-shaped or ellipsoidal. Chlamydospores are subglobose, solitary, borne on undifferentiated hyphae. Blastoconidia sometimes develop on hyphae laterally. Conidia appear arthrosporous, terminal or intercalary, aerial on an agar surface. The conidia size ranges from 4.8 to 12.5 μm x 2.4–2.5 μm.^{[citation needed]}

G. candidum is thought to be homothallic but most isolates are self-sterile. Sexual reproduction was first observed in strains isolated from soils in Puerto Rico. The fungus produces globose asci that contain a single, thick walled, uninucleated, globose to oval ascospore measuring 6–7 μm by 7–10 μm. The ascospores have a smooth inner wall and a furrowed outer wall. The septa are perforated by microspores, arranged in a ring structure. The colonies appear to be growing faster in the sexual stage than the asexual stage. Colonies grow at a rate of 5–7 mm daily at 24 °C (75 °F).