Thielavia subthermophila
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| Thielavia subthermophila | |
|---|---|
Scientific classification  | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Sordariomycetes |
| Order: | Sordariales |
| Family: | Chaetomiaceae |
| Genus: | Thielavia |
| Species: | T. subthermophila |
| Binomial name | |
| Thielavia subthermophila Mouch. (1973) | |
Thielavia subthermophila is a ubiquitous, filamentous[1] fungus that is a member of the phylum Ascomycota and order Sordariales.[2] Known to be found on plants of arid environments, it is an endophyte with thermophilic properties, and possesses dense, pigmented mycelium.[2][3][4] Thielavia subthermophila has rarely been identified as a human pathogen, with a small number of clinical cases including ocular and brain infections.[1][2] For treatment, antifungal drugs such as amphotericin B have been used topically or intravenously, depending upon the condition.[1][2]
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]
Morphology
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]
Growth
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]
Ecology
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]
Metabolites
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]