''Chaetomium atrobrunneum'' is a darkly pigmented mould affiliated with the fungal division,

Ascomycota 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 def ...

. This species is predominantly saprotrophic, although it has been known to infect animals including humans, showing a proclivity for the tissues of the central nervous system. ''Chaetomium atrobrunneum'' was described in 1949 from a mouldy military mattress cover obtained from the island of

Guadalcanal Guadalcanal (; indigenous name: ''Isatabu'') is the principal island in Guadalcanal Province of Solomon Islands, located in the southwestern Pacific Ocean, northeast of Australia. It is the largest island in the Solomons by area and the second- ...

Growth and morphology

''Chaetomium atrobrunneum'' is a darkly pigmented, predominantly mycelial fungus. Colonies of ''C. atrobrunneum'' typically are dark grey to black in colour with a woolly appearance. It forms sexual fruiting structures called

perithecia An ascocarp, or ascoma (: ascomata), is the fruiting body ( sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores. Ascoc ...

that are spherical to oval in shape, measuring between 70 and 150 μm in width when fully matured at 10 days. The perithecia are covered sparsely with straight, finely-blistered, dark brown hairs that become occasionally become broadly branched with age. The perithecia contain asci within which are 8

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 ...

s that spindle-shaped, have a single sub-apical germ pore and are brown to grey in colour, although a mutant with colourless ascospores has been reported. The ascospores of this species are smooth-walled and measure 9–11 μm in length by 4.5–6 μm in width.

Ecology and physiology

''Chaetomium atrobrunneum'' has been reported from rabbit dung, milled Italian rice, water-damaged building materials, concrete, plaster and wallpaper. ''Chaetomium atrobrunneum'' grows more slowly at than most other species of the genus, reaching a colony diameter of 16–21 mm after 7 days incubation on

Cornmeal Maize meal is a meal (coarse flour) ground from dried maize. It is a common staple food and is ground to coarse, medium, and fine consistencies, but it is not as fine as wheat flour can be.Herbst, Sharon, ''Food Lover's Companion'', Third Editi ...

Agar (CMA). By contrast, its growth at higher temperatures is much more rapid than many other ''Chaetomium'' species, producing colonies of approximately 41–44 mm in diameter after 7 days incubation at on CMA. ''Chaetomium atrobrunneum'' is distinct from other ''Chaetomium'' species by its smaller perithecia, its ability to grow at relatively high temperatures, and the occasional presence in this taxon of perithecial hairs that branch at wide angles. ''Chaetomium atrobrunneum'' is strongly cellulolytic, and cellulose-containing growth media can be used to selectively cultivate this and other ''Chaetomium'' species. This species has also been reported to produce chaetoatrosin A, a selective inhibitor of

chitin synthase In enzymology, a chitin synthase () is an enzyme that catalyzes the chemical reaction :UDP-N-acetyl-D-glucosamine + ,4-(N-acetyl-beta-D-glucosaminyl) \rightleftharpoons UDP + ,4-(N-acetyl-beta-D-glucosaminyl)+1 Thus, the two substrates of thi ...

II. This enzyme is involved in

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

formation and cellular division, and its inhibition by chaetoatrosin A is thought to be the mechanism underlying the antifungal effects of ''C. atrobrunneum'' culture filtrates against several medically important fungi including ''

Cryptococcus neoformans ''Cryptococcus neoformans'' is an encapsulated basidiomycetous yeast belonging to the class Tremellomycetes and an obligate aerobe that can live in both plants and animals. Its teleomorph is a filamentous fungus, formerly referred to ''Filob ...

''.

Pathogenicity

''Chaetomium atrobrunneum'' is a rare pathogen of humans that tends to infect the tissues of the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...

. Its pathogenicity is thought to be supported by its ability to grow at high temperatures. This species has been reported to be an agent of fatal brain abscesses in immunologically impaired people. It can also cause systemic disseminated

phaeohyphomycosis Phaeohyphomycosis is a diverse group of fungal infections, caused by dematiaceous fungi whose morphologic characteristics in tissue include hyphae, yeast-like cells, or a combination of these. It can be associated with an array of melanistic fil ...

affecting other organs including the lungs. Infections due to this species have typically occurred following invasive procedures such as intravenous drug administration and renal transplantation. In addition to deep mycotic disease, ''C. atrobrunneum'' is known to eye diseases including

retinitis Retinitis is inflammation of the retina in the eye, which can permanently damage the retina and lead to blindness. The retina is the eye's "sensing" tissue. Retinitis may be caused by a number of different infectious agents. Its most common form, ...

and

keratitis Keratitis is a condition in which the human eye, eye's cornea, the clear dome on the front surface of the eye, becomes inflammation, inflamed. The condition is often marked by moderate to intense pain and usually involves any of the following sy ...

, manifesting with symptoms of pain, redness and watering of the eye, and swelling of the eyelid and surrounding tissues. Corneal infections have responded to dual therapy with topical

natamycin Natamycin, also known as pimaricin, is an antifungal medication used to treat fungal infections around the eye. This includes infections of the eyelids, conjunctiva, and cornea. It is used as eyedrops. Natamycin is also used in the food in ...

and oral

ketoconazole Ketoconazole, sold under the brand name Nizoral, among others, is an antiandrogen, antifungal drug, antifungal, and antiglucocorticoid medication used to treat a number of fungal infections. Applied to the skin it is used for fungal skin inf ...

. This species has been reported from infections of the skin surrounding the eye. Co-administration of the antifungal drugs

fluconazole Fluconazole is an antifungal medication used for a number of fungal infections. These include candidiasis, blastomycosis, coccidioidomycosis, cryptococcosis, histoplasmosis, dermatophytosis, and tinea versicolor. It is also used to pr ...

(delivered topically) and

itraconazole Itraconazole, sometimes abbreviated ITZ, is an antifungal medication used to treat a number of fungal infections. This includes aspergillosis, blastomycosis, coccidioidomycosis, histoplasmosis, and paracoccidioidomycosis. It may be given ...

(delivered orally) have been effective in the treatment of cutaneous disease. Skin infections are thought to result from direct contact with environmental reservoirs of ''C. atrobrunneum'' such as soil, and accordingly farmers or children may have greater susceptibility.

References

External links

* * {{Taxonbar, from=Q10447608 atrobrunneum Fungi described in 1949 Fungal pathogens of humans Fungus species