Botryotrichum piluliferum

Botryotrichum piluliferum was first described in Belgium[6] from rabbit dung.[4] The anamorph was discovered by Pier Andrea Saccardo and Marchal in 1885.[1] The teleomorph, Chaetomium piluliferum was named by J. Daniels in 1961 from a culture of B. piluliferum on cellulose film.[2] The culture produced underdeveloped perithecia typical of those seen in the genus Chaetomium but was not connected to any known species at the time.[2] The culture also produced phialospores and dark hyphae that were characteristic of B. piluliferum.[2] Daniels described this as the teleomorph of B. piluliferum and named it C. piluliferum.[2]

A dried type specimen of the teleomorph was studied and found to be similar to C. murorum, a species described by Corda in 1837.[4] This fungus contained narrower ascospores, longer hairs of ascomata, and was absent of aleurioconidia and an anamorph.[7] The conidiophores of C. piluliferum resemble that of C. piluliferoides which was discovered by Udagawa and Horie in 1975.[4] C. piluliferoides produces aleurioconidia 5–7.5 μm in diameter and ascomata that are 200-240 x 120-145 μm containing short terminal hairs of 200-250 μm and spindle-shaped ascospores.[4]

Hawksworth stated that understanding C. piluliferum could not be done using only the anamorph[4] and expressed the need for further research on the Botryotrichum states which occur in three Farrowia and eight other Chaetomium species.[4] C. piluliferum has the most complex conidiophores, (sub)hyaline aleurioconidia, and a thick wall.[4] The others, such as B. atrogriseum, discovered by van Beyma in 1928 and B. peruvianum, discovered by Matsushima in 1975 have similar-sized aleurioconidia and are pigmented.[4]

The colonies of B. piluliferum are fast-growing.[4] They can spread from 2.0 to 4.3 cm in diameter in one week when grown at 20 °C (68 °F).[4] The colonies start off as white aerial mycelium which can become a yellowish-beige colour by the subsequent production of brown, rough-walled sterile setae.[4] These brown setae are about 250 x 2-5 μm and bumpy or encrusted near their base.[5] The conidiophores branch at right angles to the main axis.[5] They are smooth, colourless, and produce conidia at their ends.[5] The conidia are thick-walled, hyaline (white), smooth, and spherical.[5] They are approximately 9-16 μm in diameter.[5] B. piluliferum also contains branched hyaline conidiophores that produce aleurioconidia in clusters.[4] The aleurioconidia are globose and typically 3.0-3.5 μm thick.[4] The fungus can produce chains of phialoconidia as well.[4] Ascomata in B. piluliferum are rare and reach maturity in four weeks at 25 °C (77 °F).[4] They are black, with a globose to subglobose shape.[4] The lateral and terminal hairs of the ascomata are 500-1500 μm long, 4-6 μm wide with an olive-brown colour and may contain tips with are rolled in a flat coil towards the center.[4] The pale brown ascospores are ellipsoidal (or football-shaped) and contain one germ pore that is roughly 13-16 x 8–10.5 μm.[4]

Mating behaviour of the fungus is unknown because single-spore cultures lose the ability to produce ascomata.[4] The teleomorph C. piluliferum is made up of colonies containing brown hyphae with rough and bumpy hairs.[7] C. piluliferum ascomata are superficial and spherical or obovate (oval-shaped with a narrow base, like a light bulb.[7] They contain a small pore on the top called and ostiole that allow spores to pass through.[7] The perithecia have brown or reddish walls[8] and are covered with thick-walled, septate ascomatal hairs that are long, brown, with many bends and turns, often with tightly coiled tips.[7] The asci are obovate (light bulb-shaped) or broadly clavate (baseball bat-shaped), have a short stalk and contain 8 spores.[7] Phialoconidia form from the apex towards the base in the form of droplets on clustered flask-shaped cells.[7]

Botryotrichum piluliferum has an optimal growth temperature range of 25–30 °C (77–86 °F), with its maximum growth temperature at 40 °C (104 °F).[4] The fungus cannot tolerate acid.[4] It can grow in alkaline pH greater than 8.8, however its optimal pH is 5.5.[4] This allows for decomposition of starch, pectin and xylan.[4] B. piluliferum produces mycotoxins that are metabolically similar to aflatoxin.[9] A mycotoxin isolated from B. piluliferum, sterigmatocystin,[10] is involved in the synthesis pathway of aflatoxin.[11] In comparison to other species like Trichoderma aureoviride, that has been found to be very susceptible to parasites, B. piluliferum shows greater resistance to mycoparasites such as Pythium oligandrum.[12] B. piluliferum also produces the metabolite cochliodinol A.[3]

Botryotrichum piluliferum is found worldwide. It has been isolated and recorded in many countries such as Canada,[13] the United States,[13] The Netherlands,[14] and South Africa.[14] It has been found on deer and goat dung in Denmark and field mouse dung in England.[4] The fungus is rarely found in soils, however, it can be found at depths of 80 cm below soil.[4] It has been reported in mountainous regions, salt marshes, and cedar forests.[4] It has also been isolated from stems of Urtica dioica, hay, rhizospheres of groundnut, rice and wheat, paper products, and mouldy textiles,[4] as well as in the seeds of chili pepper.[9] B. piluliferum is a food source for Pygmephorus mesembrinae and P. quadratus.[4] When in vitro, it can be parasitized by Pythium oligandrum.[4]