Species ofThamnostylumform apophysate sporangia with deliquescent walls from the apex of the main sporangiophore or its branches. Persistent-walled sporangia are also apophystate and they are borne on curved to recurved, elongate pedicels. Zygospores have a rough, dark, ornamented zygosporangium, and opposed, more or less equal suspensors.(Zygomycetes.org 2015)
Thamnostylum piriformeis one of the most commonly encountered members of the Mucoraceae; it probably can be collected worldwide. The other species ofThamnostylumhave a more restricted distribution (Benny and Benjamin, 1975).
Four species are recognized that can be isolated from dung (Benny and Benjamin 1975). Upadhyay (1973) tranferredHelicostylum repenstoThamnostylum. (Zygomycetes.org 2015)A number of studies have been done to explore T. piriforme’s potential for chemical biotransformation. It is able to transform hydroxylate acids in relatively high yields. It has also been known to transform steroids in a region-selective and stereo-selective manner. One such study reports hydroxylation (adding a hydroxyl group) to 14α-position of steroids including progesterone. This activated molecule can then be converted to more important steroids for research and medical purpose, mainly cardio-active steroids implicated in signaling of the heart muscle. In a screen of many different fungi for the ability to convert progesterone, T. piriforme had one of the highest yields. In the most successful trials, it produced about 85% of the 14α-hydroxylation, and 15% of a minor 9a-hydroxy derivative (Eppstein et al., 1958; Hu, Genain, & Azerad, 1995). A 1980 study found that this fungus could also hydroxylate lithocholic acid, an acid of the bile (Hayakawa, Yao, Lijima, & Sasaki, 1980).
Thamnostylum piriforme has shown sensitivity to penicillin anti-fungal proteins (PAF). In germination assays it was only slightly sensitive compared to other species of zygomycetes (0-50% inhibition). However, in growth assays it showed higher sensitivity, and rated highly sensitive with up to a 7mm inhibition zone (Galgóczy et al., 2005).
Another study investigated whether the fungus itself was toxic to other micro-organisms. It had no lethality again shrimp brine (Artemia salina), whereas other Mucorales had up to 74% lethality (Reiss, 1993).
In 1880, Bainier first described this fungus in a bulletin of the French botanical society calling it Helicostylum piriforme. Later it was re-assigned to the genus Thamnidium as Thamnidium piriforme in 1910 by Arx & H.P Upadhyay (Bensch, n.d.). Finally in 1970 it was assigned to its current genus as Thamnostylum piriforme (Benny, 1992; Donnell et al., 2001).
Its current classification is as follows: Fungi, Mucoromycota, Mucoromycotina, Mucorales, Thamnidiaceae, Thamnostylum.
Researchers have successfully cultured T. piriforme on Potato Dextrose Agar (PDA) and Standard Methods Agar (SMA) (Mehrotra, Madhava Das Mehrotra, 1962)and can also be readily cultivated on gelatin, agar, and bread (William, 1915). Although most fungi in this genus grow optimally at 25°C (Benny, 1995), physiological studies in 1962 demonstrate temperature rate of growth was enhanced up to 30°C, after which there was a decline in growth. Optimal temperature of sporulation was a bit warmer at 34°C. Low pH values proved to be toxic, and negative to the growth of the fungus. Optimal pH appeared to be at pH6 or pH9.5 for both sporulation and growth (Mehrotra, Madhava Das Mehrotra, 1962). This bi-modal nature is thought to be due to change in permeability for salts or the fact that solubility of salts can differ at different pH (Arrhenius, 1922).
Growth assays with T. piriforme show it is able to hydrolyze only maltose and raffinose. However, it can utilize and grow well on galactose, xylose, raffinose, mannitol and sorbitol (Mehrotra, Madhava Das Mehrotra, 1962). For nitrogen requirements, nitrite nitrogen proved to be the best form. Out of the eight compounds test, glutamic acid demonstrated the best ability to induce zygospore formation. As far as amino acid utilization, phenylalanine, arginine, glutamic acid and histidine all can be utilized. Leucine, histidine, glutamic acid and arginine are more efficiently utilized together than singly. Histidine and tryptophan cannot be metabolized when given singly (Mehrotra, 1964).
Fungi in the order Mucorales are usually ubiquitous, and often grow saprotrophically on decaying organic matter. In general, these fungi do not utilize cellulose or lignin, so rather they need less complex, soluble sources of carbon and nitrogen (Misra, Tewari, & SK, 2012).
Even though relatively little is known of Mucorales, it is one of the most studied group from early diverging fungi (Hoffmann et al., 2013). Thamnostylum piriforme in particular is one of the most commonly found members of Mucoraceae. It is postulated that it may be collected worldwide. This is in contrast to other species of Thamnostylum that have a more restricted distribution (Benny, 2005).
Thamnostylum piriforme is commonly isolated from rabbit, pig, and rat dung (Vesco, Peyronel, Barge, & Volpiana, 1967). It has also been found on horse dung. Generally, zygomycetes are some of the earliest colonizers of dung, but this species tends to colonize a bit slower compared to other zygomycetes (Piontelli, Santa-maria, & Caretta, 1981).
A 1889 description of T. piriforme in culture describes it as gray and dense, and as the culture ages turning darker brownish black (William, 1915).
Production of stolons is an autapomorphy of T. piriforme used to distinguish this species (Benny, 1995). No odor is associated with T. piriforme in contrast to others in the family which can produce a fruity odor. Also unique to T. piriforme is its ability to produce rhizoids (Donnell, Lutzoni, Ward, & Benny, 2001).
Sporangia contain a few (but always more than one) spores with a persistent wall and a reduced columnella (Benny, 1995)that is hyaline, oval to pyriform (William, 1915). The sporangial wall is also described as deliquescent (Benny, 1995; Mehrotra, Madhava Das Mehrotra, 1962; William, 1915).
Mehrotra describes in detail in his 1962 description saying, “sporangiophores mostly erect, simple or branched 12-30µm in width, either terminating into a sporangium. Sporangium spherical 90-125µm, spores ellipsoidal 5-10.5 X 4-6µm. Sporangiola, borne in pairs or clusters on multiple short branchlets arising from one or more prominent nodal swellings on each sporangiophore, reflexed onto the pedicels, pyriform in shape, 12-23 X 12-21µm” (Mehrotra, Madhava Das Mehrotra, 1962).The sporangioles may arise in clusters of 3-4 either as forkings or as short lateral branches. However, it has been reported to bare 100 or more sporangioles in clusters on whorls of the sporangiophore. Up to five or six clusters have been found on a single sporangiophore, almost appearing as beads loosely strung in a row (William, 1915).
Zygospores can be described as “rough, dark, ornamented” with suspensors that are “opposed, more or less equal” (Benny, 2005). M.D Mehrotra’s description of zygospores explains that they are produced between opposed suspensors and “globose, 71-165 X 66-154µm mostly 99-143 X 88-137µm, surface warty” (Mehrotra, Madhava Das Mehrotra, 1962).
Thamnostylum piriforme is found in clade 2 of the Mucorales and used as the type species for the genera Thamnostylum (Bensch, n.d.; Donnell et al., 2001; Hoffmann et al., 2013). With molecular analysis Thamnidiaceae was found to be polyphyletic (Donnell et al., 2001). Species traditionally assigned to Thamnidiaceae were found scattered over the entire order. Further analysis is needed, as relationships within the Mucorales is still rather unstable. The family Thamnidiaceae most recently is published as containing the following genera: Backusella, Cokeromyces, Ellisomyces, Fennellomyces, Helicostylum, Kirkomyces, Pahscolomyces, Pirella, Thamnidium, Thamnostylum, and Zychaea (Donnell et al., 2001; Hoffmann et al., 2013).
Thamnostylum piriforme is a heterothallic fungus, meaning in order for it to sexually reproduce it requires physical interaction of isolates belonging to the opposite mating types(Benny, 2005). If both mating types are present and conditions are right, zygospores can form and meiosis can then occur. Although not studied for Thyamnostylum specifically, sexual reproduction in Mucorales is thought to be initiated by volatiles that are used in communication between two mating types, and mating type compatibility is thought to be genetically coded (Hoffmann et al., 2013). Asexually, this fungus produes spores from sporangia. T. piriforme produces dry spores that are dispersed through air movements, in contrast to other members of Mucorales that are produced in water droplets and dispersed only with moisture. (Hayakawa, Yao, Lijima, & Sasaki, 1980).
