Dimorphic fungi are

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

that can exist in the form of both

mold A mold () or mould () is one of the structures certain fungi can form. The dust-like, colored appearance of molds is due to the formation of spores containing fungal secondary metabolites. The spores are the dispersal units of the fungi. Not ...

and

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constit ...

. This is usually brought about by change in temperature and the fungi are also described as thermally dimorphic fungi. An example is ''

Talaromyces marneffei ''Talaromyces marneffei'', formerly called ''Penicillium marneffei'', was identified in 1956. The organism is endemic to southeast Asia where it is an important cause of opportunistic infections in those with HIV/AIDS-related immunodeficiency. ...

'', a human pathogen that grows as a mold at

room temperature Colloquially, "room temperature" is a range of air temperatures that most people prefer for indoor settings. It feels comfortable to a person when they are wearing typical indoor clothing. Human comfort can extend beyond this range depending on ...

, and as a yeast at human

body temperature Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperatur ...

. The term dimorphic is commonly used for fungi that can grow both as yeast and filamentous cells, however many of these dimorphic fungi actually can grow in more than these two forms. Dimorphic is thus often used as a general reference for fungi being able to switch between yeast and filamentous cells, but not necessary limiting more shapes.

Ecology of dimorphic fungi

Several species of dimorphic fungi are important pathogens of humans and other animals, including ''

Coccidioides immitis ''Coccidioides immitis'' is a pathogenic fungus that resides in the soil in certain parts of the southwestern United States, northern Mexico, and a few other areas in the Western Hemisphere. Epidemiology ''C. immitis'', along with its relati ...

'', ''

Paracoccidioides brasiliensis ''Paracoccidioides brasiliensis'' is a dimorphic fungus and one of the two species that cause paracoccidioidomycosis (the other being '' Paracoccidioides lutzii).'' The fungus has been affiliated with the family Ajellomycetaceae (division Ascomyc ...

'', ''

Candida albicans ''Candida albicans'' is an opportunistic pathogenic yeast that is a common member of the human gut flora. It can also survive outside the human body. It is detected in the gastrointestinal tract and mouth in 40–60% of healthy adults. It is usu ...

'', ''

Blastomyces dermatitidis ''Blastomyces dermatitidis'' is a dimorphic fungus that causes blastomycosis, an invasive and often serious fungal infection found occasionally in humans and other animals. It lives in soil and wet, decaying wood, often in an area close to a wat ...

'', ''

Histoplasma capsulatum ''Histoplasma capsulatum'' is a species of dimorphic fungus. Its sexual form is called ''Ajellomyces capsulatus''. It can cause pulmonary and disseminated histoplasmosis. ''H. capsulatum'' is "distributed worldwide, except in Antarctica, but m ...

'', '' Sporothrix schenckii'', and ''

Emmonsia ''Chrysosporium'' is a genus of hyaline hyphomycetes fungi in the family Onygenaceae. ''Chrysosporium'' colonies are moderately fast-growing, flat, white to tan to beige in color; they often have a powdery or granular surface texture. Hyaline, ...

'' sp. Some diseases caused by the fungi are: *

sporotrichosis Sporotrichosis, also known as rose handler's disease, is a fungal infection that affects skin, lungs, bone and joint, and can be widespread. It presents with firm painless nodules that later ulcerate. It can be localized or widespread. The disea ...

blastomycosis Blastomycosis or blasto is a fungal infection caused by inhaling spores of a ''Blastomyces'' fungus. Only about half of people with the disease have symptoms, which can include fever, cough, night sweats, muscle pains, weight loss, chest pain, ...

histoplasmosis Histoplasmosis is a fungal infection caused by '' Histoplasma capsulatum''. Symptoms of this infection vary greatly, but the disease affects primarily the lungs. Occasionally, other organs are affected; called disseminated histoplasmosis, it can ...

coccidioidomycosis Coccidioidomycosis (, ), commonly known as cocci, Valley fever, as well as California fever, desert rheumatism, or San Joaquin Valley fever, is a mammalian fungal disease caused by '' Coccidioides immitis'' or ''Coccidioides posadasii''. Coccid ...

paracoccidioidomycosis Paracoccidioidomycosis (PCM), also known as South American blastomycosis, is a fungal infection that can occur as a mouth and skin type, lymphangitic type, multi-organ involvement type (particularly lungs), or mixed type. If there are mouth ulce ...

talaromycosis Talaromycosis is a fungal infection that presents with painless skin lesions of face and neck, fever, anaemia, large lymph glands and liver. It is caused by the fungus''Talaromyces marneffei'', which is found in soil and decomposing organic ma ...

candidiasis Candidiasis is a fungal infection due to any type of '' Candida'' (a type of yeast). When it affects the mouth, in some countries it is commonly called thrush. Signs and symptoms include white patches on the tongue or other areas of the mouth ...

Many other fungi, including the plant pathogen ''

Ustilago maydis Corn smut is a plant disease caused by the pathogenic fungus ''Ustilago maydis'' that causes smut on maize and teosinte. The fungus forms galls on all above-ground parts of corn species. It is edible, and is known in Mexico as the delica ...

'' and the cheesemaker's fungus ''

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 w ...

'' also have dimorphic life cycles.

Mnemonics

In medical mycology, these memory aids help students remember that among human pathogens, dimorphism largely reflects temperature: * Mold in the Cold, Yeast in the Heat (Beast) * Body Heat Probably (Changes) Shape ** ''

'', ''

'', (''

'') is in parentheses because it changes to a

spherule A sphere () is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. A sphere is the set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the ...

of endospores, not yeast, in the heat), '' Sporothrix schenckii''. ** This phrase says "Probably" because there is always an exception (in this case fungi like ''

'') which change in the opposite direction: to mold in the heat!

Notes

References

{{Mycoses Fungal morphology and anatomy