| Geotrichum candidum | |
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| Geotrichum candidum | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Saccharomycetes |
| Order: | Saccharomycetales |
| Family: | Dipodascaceae |
| Genus: | Geotrichum |
| Species: | G. candidum |
| Binomial name | |
| Geotrichum candidum Link (1809) | |
| Synonyms | |
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Geotrichum candidum is afungus which is a member of thehuman microbiome, notably associated with skin,sputum, and faeces where it occurs in 25–30% of specimens.[1][2] It is common in soil and has been isolated from soil collected around the world, in all continents.[1]
G. candidum is the causative agent of the human diseasegeotrichosis and the plant diseasesour rot which infectscitrus fruits,tomatoes,carrots, and other vegetables.[3] It can affect harvested fruit ofdurians such asDurio graveolens.[4]
G. candidum is used widely in the production of certain dairy products including rind cheeses such asCamembert,Saint-Nectaire,Reblochon, and others. The fungus can also be found in aNordicyogurt-like product known asviili where it is responsible for the product's velvety texture.[5]
In a 2001 study,G. candidum was found to consume thepolycarbonate found inCDs.[6]
The genusGeotrichum was described byJohann Heinrich Friedrich Link in 1809 to accommodate the speciesG. candidum found on decaying leaves. Since then, over 130 taxa have been described in the genus, and hundreds of synonyms have been generated.[7] For example,G. candidum was misclassified as theOidium lactis in much early literature.[8] Species ofGeotrichum resemble the generaTrichosporon andProtendomycopsis; however,Geotrichum is ofascomycetous affiliation whereas the latter are members of theBasidiomycota. Species ofGeotrichum are occasionally mistaken for fast growing members of the genusDipodascus, which are characterized by irregularly branched, 10–14 μm widehyphae and the production of single-sporedasci. However, unlikeGeotrichum, members of the genusDipodascus lack dichotomous branching of the peripheral hyphae and their growth rates are generally less than 3 mm per day.[1]
Galactomyces candidus, formerly thought to be a distinct taxon, was found to be thesexual state ofG. candidum using sequence-based methods[9][10]Geotrichum candidum in the broad sense comprises 3clades, corresponding to the speciesG. candidum,G. clavatum andG. fici, all of which are thought to have pathogenic potential.[5][2][11] Species ofGeotrichum can be differentiated by sequence analysis of the nuclear ribosomal large subunit (18S ribosomal RNA) or theinternal transcribed spacer region of the nuclear ribosomal RNA gene.[9]
G. candidum colonies are thin, spreading, soft, creamy and white in theanamorph state.[12] The fungusG. candidum is characterized by hyphae that appear creeping, mostly submerged andseptate.[1][13] The hyphae colour appears to behyaline or lightly pigmented.[14] When the hyphae becomes airborne it changes shape fromarthroconidia to cylindrical or barrel-shaped or ellipsoidal.[1]Chlamydospores are subglobose, solitary, borne on undifferentiated hyphae.[1][13]Blastoconidia sometimes develop on hyphae laterally.[1]Conidia appear arthrosporous, terminal or intercalary, aerial on an agar surface. Theconidia size ranges from 4.8 to 12.5 μm x 2.4–2.5 μm.[citation needed]
G. candidum is thought to behomothallic but most isolates are self-sterile.[1] Sexual reproduction was first observed in strains isolated from soils inPuerto Rico.[15] The fungus produces globose asci that contain a single, thick walled,uninucleated, globose to ovalascospore measuring 6–7 μm by 7–10 μm.[1] The ascospores have a smooth inner wall and a furrowed outer wall.[15] The septa are perforated bymicrospores, 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).[1]
Geotrichum candidum forms a fast growing colony that can grow to 5–6 cm diameter at 5 days onSabouraud-glucose agar, wort agar and synthetic media. Microscopically, the growth is characterized by the production ofdichotomously branched hyphae that resembletuning 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 0–5 °C (32–41 °F). The conidia are colourless and have a slimy coating.[16]G. candidum is also found occasionally in the human gut,feces,sputum and on skin. The fungus grows in soil, water, sewage, various plant substrates, baker's dough, husks of fermentation, bread, milk and milk products[1] The optimal temperature for growth is 25 °C (77 °F) with a pH range of 5.0–5.5.[8] The temperature range changes depending on the surface that the fungus grows on. For example, in plants the optimum temperature ranges from 25–27 °C (77–81 °F). In animals the optimum temperature ranges from 30–31 °C (86–88 °F).[17] The maximum temperature for growth is 35–38 °C (95–100 °F).[1][12] Fungal growth can be supported byD-glucose,D-mannose,D-xylose,L-sorbose,D-fructose,D-galactose,sucrose,D-mannitol,D-sorbital,ethanol andglycerol. Sporulation often requires a balance of carbon and nitrogen.[1]
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.[1] 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.[18] 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 0–5 °C (32–41 °F).[1]
It is a naturally occurring colonist of certain dairy products (particularly cheeses) and is sometimes used to inoculate wash-rind andbloomy rind cheeses.[8][9][19]
G. candidum can be used commercially to inoculatewash-rinds andbloomy rind cheeses.[8][9][19] 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.[8] For the Camembert cheese the fungi grows on the outside of the cheese forming a rind.[19] The fungus is responsible for the uniform, white, velvety coat onSaint-Marcellin cheese.[8] Lipases and proteases fromG. 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 theaminopeptidases that hydrolyze low molecular weight hydrophobic peptides. Aminopeptidases also contributes an aroma in traditional Norman Camembert. The fungus also neutralizes the curd by catabolizinglactic acid produced by bacteria.G. candidum prepares the cheese for colonization of other acid sensitive bacteria such asBrevibacterium. The fungus inhibits growth of the bacteriaListeria monocytogenes.[20] Commercial strains ofG. candidum are available for cheese ripening.[8]
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