''Geotrichum candidum'' is a fungus which is a member of the

human microbiome The human microbiome is the aggregate of all microbiota that reside on or within human tissues and biofluids along with the corresponding anatomical sites in which they reside, including the skin, mammary glands, seminal fluid, uterus, ovarian ...

, 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 cytological investigations ...

, 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 Geotrichosis is a mycosis caused by ''Geotrichum candidum''. Human colonization and disease ''Geotrichum candidum'' is also a frequent member of the human microbiome, notably associated with skin, sputum and feces where it occurs in 25-30% of spec ...

, the plant disease sour rot which infects citrus fruits, tomatoes,

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

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 recognised ''Durio'' species, at least nine of which produce edible fruit. ''Durio zibethinus'', native to Borneo and Sumatra, is the onl ...

s 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 Viili (Finnish) is a mesophilic fermented milk product found in the Nordic countries The Nordic countries (also known as the Nordics or ''Norden''; literal translation, lit. 'the North') are a geographical and cultural region in Northern E ...

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 groups in their chemical structures. Polycarbonates used in engineering are strong, tough materials, and some grades are optically transparent. They are easily work ...

found in CDs. This effect was later replicated in 2021.

History

Taxonomy

The genus ''

Geotrichum Geotrichum is a genus of fungi found worldwide in soil, water, air, and sewage, as well as in plants, cereals, and dairy products; it is also commonly found in normal human flora and is isolated from sputum and feces. It was first described in ...

'' was described by

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

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 ''Trichosporon'' is a genus of anamorphic fungi in the family Trichosporonaceae. All species of ''Trichosporon'' are yeasts with no known teleomorphs (sexual states). Most are typically isolated from soil, but several species occur as a natural ...

'' and ''Protendomycopsis''; however, ''Geotrichum'' is of

ascomycetous Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The de ...

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 or ...

e and the production of single-spored

asci ASCI or Asci may refer to: * Advertising Standards Council of India * Asci, the plural of ascus, in fungal anatomy * Accelerated Strategic Computing Initiative * American Society for Clinical Investigation * Argus Sour Crude Index * Association of ...

. 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 A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

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. The S in 18S represents Svedberg units. 18S rRNA is an SSU rRNA, a component of the eukaryotic ribosomal small subunit (40S). 18S rRNA is the structural RNA for the small c ...

) or the internal transcribed spacer region of the nuclear ribosomal RNA gene.

Morphology

Anamorph

''G. candidum'' colonies are thin, spreading, soft, creamy and white in the

anamorph In mycology, the terms teleomorph, anamorph, and holomorph apply to portions of the life cycles of fungi in the phyla Ascomycota and Basidiomycota: *Teleomorph: the sexual reproductive stage (morph), typically a fruiting body. *Anamorph: an ase ...

state. The fungus ''G. candidum'' is characterized by hyphae that appear creeping, mostly submerged and septatee. The hyphae colour appears to be

hyaline A hyaline substance is one with a glassy appearance. The word is derived from el, ὑάλινος, translit=hyálinos, lit=transparent, and el, ὕαλος, translit=hýalos, lit=crystal, glass, label=none. Histopathology Hyaline cartilage is ...

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

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

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

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. 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 .

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 forks 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 ( or faeces), known colloquially and in slang as poo and poop, 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 large intestine. Feces contain a relati ...

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 monomer of the aldohexose series of carbohydrates. It is a C-2 epimer of glucose. Mannose is important in human metabolism, especially in the glycosylation of certain proteins. Several congenital disorders of glycosylation are ...

, D-xylose, L-sorbose,

D-fructose Fructose, or fruit sugar, is a ketonic simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorbed ...

, 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 and glycerol. 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 Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

, 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 sometime 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 Saint-Marcellin is a soft French cheese made from cow's milk. Named after the small town of Saint-Marcellin ( Isère), it is produced in a geographical area corresponding to part of the former Dauphiné province (now included in the Rhône-Alpes ...

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 aminopeptidases 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 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, South Australia * Andreas Späth ''et al''.
X‑ray microscopy reveals the outstanding craftsmanship of Siberian Iron Age textile dye
In: Nature Scientific Reports; (2021) 11:5141. doi:10.1038/s41598-021-84747-z. See also:
Scientists solve mystery behind world's oldest 'Pazyryk' carpet
Daily Sabah, Istanbul, Mar 23, 2021 on Pazyryk carpet.