''Geotrichum candidum'' is a

fungus A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

which is a member of the human microbiome, notably associated with skin,

sputum Sputum is mucus that is coughed up from the lower airways (the trachea and bronchi). In medicine, sputum samples are usually used for a naked-eye examination, microbiological investigation of respiratory infections, and Cytopathology, cytological ...

, 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 ''Citrus'' is a genus of flowering trees and shrubs in the family Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, mandarins, lemons, grapefruits, pomelos, and limes. ''Citrus'' is nativ ...

fruits,

tomato The tomato (, ), ''Solanum lycopersicum'', is a plant whose fruit is an edible Berry (botany), berry that is eaten as a vegetable. The tomato is a member of the nightshade family that includes tobacco, potato, and chili peppers. It originate ...

es,

carrot The carrot ('' Daucus carota'' subsp. ''sativus'') is a root vegetable, typically orange in colour, though heirloom variants including purple, black, red, white, and yellow cultivars exist, all of which are domesticated forms of the wild ...

s, and other vegetables. It can affect harvested fruit of

durian The durian () is the edible fruit of several tree species belonging to the genus ''Durio''. There are 30 recognized species, at least nine of which produce edible fruit. ''Durio zibethinus'', native to Borneo and Sumatra, is the only species ...

s such as '' Durio graveolens''. ''G. candidum'' is used widely in the production of certain dairy products including rind cheeses such as

Camembert Camembert ( , , ) is a moist, soft, creamy, surface-ripened cow's milk cheese. It was first made in the late 18th century in Camembert, Normandy, in northwest France. It is sometimes compared in look, taste and texture to brie cheese, albe ...

, Saint-Nectaire,

Reblochon Reblochon () is a soft washed-rind and smear-ripened French cheese made in the Alpine region of Haute-Savoie from raw cow's milk. It has its own AOC designation. Reblochon was first produced in the Thônes and Arly valleys, in the Aravis ...

, and others. The fungus can also be found in a Nordic

yogurt Yogurt (; , from , ; also spelled yoghurt, yogourt or yoghourt) is a food produced by bacterial Fermentation (food), fermentation of milk. Fermentation of sugars in the milk by these bacteria produces lactic acid, which acts on milk protein to ...

-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 Polycarbonates (PC) are a group of thermoplastic polymers containing carbonate ester, carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, toughness, tough materials, and some grades are optically transp ...

found in CDs.

History

Taxonomy

The genus '' Geotrichum'' was described by

Johann Heinrich Friedrich Link Johann Heinrich Friedrich Link (2 February 1767 – 1 January 1851) was a German natural history, naturalist and botanist. Biography Link was born at Hildesheim as a son of the minister August Heinrich Link (1738–1783), who taught him love ...

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 Basidiomycota () is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya (often referred to as the "higher fungi") within the kingdom Fungi. Members are known as basidiomycetes. More specifically, Basi ...

. Species of ''Geotrichum'' are occasionally mistaken for fast growing members of the genus '' Dipodascus'', which are characterized by irregularly branched, 10–14 μm wide

hypha 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 ...

e 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.

Phylogeny

''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

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

s, 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 18S ribosomal RNA (abbreviated 18S rRNA) is a part of the ribosomal RNA in eukaryotes. It is a component of the Eukaryotic small ribosomal subunit (40S) and the cytosolic homologue of both the 12S ribosomal RNA, 12S rRNA in mitochondria and the 1 ...

) or the

internal transcribed spacer Internal transcribed spacer (ITS) is the spacer DNA situated between the small-subunit ribosomal RNA (rRNA) and large-subunit rRNA genes in the chromosome or the corresponding transcribed region in the polycistronic rRNA precursor transcript. ...

region of the nuclear ribosomal RNA gene.

Morphology

Anamorph

''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 In biology, a septum (Latin for ''something that encloses''; septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interatrial se ...

. The hyphae colour appears to be

hyaline A hyaline substance is one with a glassy appearance. The word is derived from , and . Histopathology Hyaline cartilage is named after its glassy appearance on fresh gross pathology. On light microscopy of H&E stained slides, the extracellula ...

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 A conidium ( ; : conidia), sometimes termed an asexual chlamydospore or chlamydoconidium (: chlamydoconidia), is an asexual, non- motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also ...

appear arthrosporous, terminal or intercalary, aerial on an agar surface. The

conidia A conidium ( ; : conidia), sometimes termed an asexual chlamydospore or chlamydoconidium (: chlamydoconidia), is an asexual, non- motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also ...

size ranges from 4.8 to 12.5 μm x 2.4–2.5 μm.

Teleomorph

''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 ; abbreviated PR), officially the Commonwealth of Puerto Rico, is a Government of Puerto Rico, self-governing Caribbean Geography of Puerto Rico, archipelago and island organized as an Territories of the United States, unincorporated territo ...

. The fungus produces globose asci that contain a single, thick walled, uninucleated, globose to oval

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 ...

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

microspore Microspores are land plant spores that develop into male gametophytes, whereas megaspores develop into female gametophytes. The male gametophyte gives rise to sperm cells, which are used for fertilization of an egg cell to form a zygote. Megaspo ...

s, 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 .

Growth

''Geotrichum candidum'' forms a fast growing colony that can grow to 5–6 cm diameter at 5 days on Sabouraud-glucose agar, wort agar and synthetic media. Microscopically, the growth is characterized by the production of dichotomously branched hyphae that resemble

tuning fork A tuning fork is an acoustic resonator in the form of a two-pronged fork with the prongs ( ''tines'') formed from a U-shaped bar of elastic metal (usually steel). It resonates at a specific constant pitch when set vibrating by striking it ag ...

s along the colony margin. The condial chains become aerial, erect or decumbent and measure 6–12(−20) x 3–6(−9) μm. The fungus can grow on a variety of citrus fruits and cause Sour Rot. It tends to cause rotting in fruits that are stored at . The conidia are colourless and have a slimy coating. ''G. candidum'' is also found occasionally in the human gut,

feces Feces (also known as faeces American and British English spelling differences#ae and oe, or fæces; : faex) are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the ...

and on skin. The fungus grows in soil, water, sewage, various plant substrates, baker's dough, husks of fermentation, bread, milk and milk products The optimal temperature for growth is with a pH range of 5.0–5.5. The temperature range changes depending on the surface that the fungus grows on. For example, in plants the optimum temperature ranges from . In animals the optimum temperature ranges from . The maximum temperature for growth is . Fungal growth can be supported by D-glucose,

D-mannose Mannose is a sugar with the formula , which sometimes is abbreviated Man. It is one of the monomers of the aldohexose series of carbohydrates. It is a C-2 epimer of glucose. Mannose is important in human metabolism, especially in the glycosylation ...

, D-xylose, L-sorbose, D-fructose, D-galactose,

sucrose Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula . For human consumption, sucrose is extracted and refined ...

, D-mannitol, D-sorbital,

ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...

and

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 ...

. Sporulation often requires a balance of carbon and nitrogen.

Distribution

''G. candidum'' is extremely common in soil and has been isolated from substrates in Canada, United States, Britain, Germany, Austria, India, South Africa, Japan, Brazil and Peru. It is also found as a causal agent in sour rot in citrus fruits— a soft rot associated with the emission of a fruity odour. The fungus is also known as a post-harvest spoilage agent of muskmelon, squash and cucumber. It plays a role in tomato fruit rot when it is stored at . It is a naturally occurring colonist of certain dairy products (particularly cheeses) and is sometimes used to inoculate wash-rind and bloomy rind cheeses.

Commercial uses

''G. candidum'' can be used commercially to inoculate wash-rinds and bloomy rind cheeses. Cultures can be added to milk, brine or sprayed onto cheese surface. The optimum pH range for growth on cheese ranges from 4.4 to 6.7. The fungus colonizes nearly the entire surface of the cheese during the early stages of ripening. It is found on soft cheeses like Camembert cheese and semi-hard cheese Saint-Nectaire and Reblochon. For the Camembert cheese the fungi grows on the outside of the cheese forming a rind. The fungus is responsible for the uniform, white, velvety coat on Saint-Marcellin cheese. Lipases and proteases from ''G. candidum'' release fatty acids and peptides that provide the cheese with distinctive flavors. ''G. candidum'' reduces the bitterness in Camembert cheese through the activity of the

aminopeptidase Aminopeptidases are enzymes that catalyze the cleavage of amino acids from the N-terminus (beginning), of proteins or peptides. They are found in many organisms; in the cell, they are found in many organelles, in the cytosol (internal cellular f ...

s that hydrolyze low molecular weight hydrophobic peptides. Aminopeptidases also contributes an aroma in traditional Norman Camembert. The fungus also neutralizes the curd by catabolizing

lactic acid Lactic acid is an organic acid. It has the molecular formula C3H6O3. It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as wel ...

produced by bacteria. ''G. candidum'' prepares the cheese for colonization of other acid sensitive bacteria such as '' Brevibacterium''. The fungus inhibits growth of the bacteria '' Listeria monocytogenes''. Commercial strains of ''G. candidum'' are available for cheese ripening.

Literature

References

External links

Mycology Online

University of Adelaide The University of Adelaide is a public university, public research university based in Adelaide, South Australia. Established in 1874, it is the third-oldest university in Australia. Its main campus in the Adelaide city centre includes many Sa ...

South Australia South Australia (commonly abbreviated as SA) is a States and territories of Australia, state in the southern central part of Australia. With a total land area of , it is the fourth-largest of Australia's states and territories by area, which in ...

* Andreas Späth ''et al''.
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