Chaetomium atrobrunneum

Chaetomium atrobrunneum is a darkly pigmented, predominantly mycelial fungus.[2] Colonies of C. atrobrunneum typically are dark grey to black in colour with a woolly appearance.[1] It forms sexual fruiting structures called perithecia that are spherical to oval in shape,[7] measuring between 70 and 150 µm in width when fully matured at 10 days.[1] The perithecia are covered sparsely with straight, finely-blistered, dark brown hairs that become occasionally become broadly branched with age.[1][3] The perithecia contain asci within which are 8 ascospores that spindle-shaped, have a single sub-apical germ pore and are brown to grey in colour,[1][3] although a mutant with colourless ascospores has been reported.[8] The ascospores of this species are smooth-walled and measure 9–11 µm in length by 4.5–6 µm in width.[1][3]

Chaetomium atrobrunneum has been reported from rabbit dung,[7] milled Italian rice,[9] water-damaged building materials, concrete, plaster and wallpaper.[10] Chaetomium atrobrunneum grows more slowly at 25 °C (77 °F) than most other species of the genus,[1][3] reaching a colony diameter of 16–21 mm after 7 days incubation on Cornmeal Agar (CMA).[11] 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 42 °C (108 °F) on CMA.[3][11] Chaetomium atrobrunneum is distinct from other Chaetomium species by its smaller perithecia, its ability to grow at relatively high temperatures,[3] and the occasional presence in this taxon of perithecial hairs that branch at wide angles.[6]

Chaetomium atrobrunneum is strongly cellulolytic,[12] and cellulose-containing growth media can be used to selectively cultivate this and other Chaetomium species.[13] This species has also been reported to produce chaetoatrosin A, a selective inhibitor of chitin synthase II. This enzyme is involved in septum formation and cellular division,[14] 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.[14]

Chaetomium atrobrunneum is a rare pathogen of humans that tends to infect the tissues of the central nervous system.[1] Its pathogenicity is thought to be supported by its ability to grow at high temperatures.[1][2] This species has been reported to be an agent of fatal brain abscesses in immunologically impaired people.[1][3][11] It can also cause systemic disseminated phaeohyphomycosis[5] affecting other organs including the lungs.[11] Infections due to this species have typically occurred following invasive procedures such as intravenous drug administration and renal transplantation.[11]

In addition to deep mycotic disease, C. atrobrunneum is known to eye diseases including retinitis[15] and keratitis,[16] manifesting with symptoms of pain, redness and watering of the eye, and swelling of the eyelid and surrounding tissues.[16] Corneal infections have responded to dual therapy with topical natamycin and oral ketoconazole.[16] This species has been reported from infections of the skin surrounding the eye.[17] Co-administration of the antifungal drugs fluconazole (delivered topically) and itraconazole (delivered orally) have been effective in the treatment of cutaneous disease.[17] 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.[17]

• Chaetomium atrobrunneum in MycoBank.
• Chaetomium atrobrunneum in Index Fungorum