Thielavia subthermophila

Thielavia subthermophila is a cleistothecial fungus that have a thin peridium, spherical ascoma, and dark-coloured ascospores.[2][5] It was first described by Jean Mouchacca in 1973 who isolated it from desert soil.[2] To date, there has been confusion in classifying species within the genus Thielavia, as the characteristics of the species are not well-differentiated from perithecial relatives in the genus Chaetomium.[2]

Thielavia subthermophila forms grey colonies with a black reverse, with dark brown, hairy, spherical ascomata that are 90−200 µm in diameter and develop within the mycelial mat.[1][2][3][4] The wall of the ascomata is made of textura epidermoidea or flattened and irregularly outlined cells measuring 6−8 µm in diameter, and is covered with dark, branching hyphae.[1][2][3][4] Aleuriospores and chlamydospores are light brown, single-celled, 5−7 × 3−5 µm in diameter, have a truncate base, and grow terminally and laterally on short branches or hyphae.[1][3][4] Thielavia subthermophila has asci measuring 20−30 × 15−22.5 µm in diameter, each containing 8 spores.[6] It has single-celled, dark olive to black, fusiform or elliptical ascospores measuring 14−20 × 8−10 µm in diameter with a subapical germ pore measuring 1−1.5 µm in diameter.[1][2][4][5][6] Compared to other species within the genus Thielavia such as Thielavia arenaria and Thielavia microspora, it is known to produce large ascospores.[6] A felt-like aerial mycelium is characteristic of T. subthermophila, consisting of septate, branched, and hyaline or dark olive hyphae and measuring 1−3 µm.[1][6]

Thielavia subthermophila shows optimal growth and survival up to 36–45 °C (97–113 °F), as determined by its thermotolerant properties, and possesses light-protection structures.[2][3][4][6] The asexual reproductive form of Thielavia subthermophila is associated with production of pale yellowish brown, smooth aleurioconidia measuring 3−4 × 2.5−3 µm in diameter, with no conidiophores present.[4][5][6] Sexual reproduction is associated with abundant production of cleistothecia that are brownish black to black, scattered, and 120−180 µm in diameter, covered by dark olive hairs.[6]

Thielavia subthermophila has been isolated from a wide range of environments, such as soil, camel hair, and desert vegetation.[1] In addition, it has been found in dried Hibiscus flower, Brazilian pepper seeds, and species of herbal plants such as "Plantaginis herba", "Plantaginis semen", and Abies webbiana.[1][6] Notably, T. subthermophila has been isolated as an endophyte of Hypericum perforatum, otherwise known as St. John's wort.[3]

Emodin is a fungal metabolite that has been isolated from Thielavia subthermophila, which inhibits the expression of cytokines, chemokines, and inflammatory modulators in vitro.[3][7] Hypericin is a fungal metabolite that has also been isolated from Thielavia subthermophila, that initiates high cytotoxicity when excited by irradiation with visible light.[3] Thielavia subthermophila isolated from the stems of Hypercium perforatum has been recognized to undergo mechanisms of emodin and hypericin biosynthesis.[3]

As with other Thielavia species, Thielavia subthermophila has rarely been identified to be involved in human fungal infections.[2]

To treat ocular infections, antifungal medication such as oral voriconazole and amphotericin B eyedrops can be administered to the patient.[1] Fortified tobramycin, fortified cefazolin, fluorometholone, and scopolamine eyedrops can also be administered if necessary, depending on the symptoms.[1] In addition, corneal abrasion can be performed on the patient to facilitate penetration of the antifungal medication.[1] Amphotericin B therapy, surgical removal of infected tissue, and immune enhancement can be used to treat cerebral phaeohyphomycosis by Thielavia subthermophila, although despite treatment, is associated with high mortality.[2] Currently, there is no accepted standard treatment for brain infections by T. subthermophila.[2]