Geomyces pannorum is a yellow-brown filamentous fungus of the phylumAscomycota commonly found in cold soil environments including thepermafrost of the Northern hemisphere.[1] A ubiquitous soil fungus, it is the most common species of the genusGeomyces; which also includesG. vinaceus andG. asperulatus.[2][3]Geomyces pannorum has been identified as an agent of disfigurement of pigments used in the 15,000-year-old paintings on the walls of theLascaux caves of France.[4] Strains ofGeomyces have been recovered from thepermafrost tunnel inFox, Alaska and radiocarbon dated to between 14,000 and 30,000 years old.[5]
The fungusGeomyces pannorum was originally described asSporotrichum pannorum from rotten cloth in Germany byJohann Heinrich Friedrich Link in 1824.[3] It was transferred to the genusChrysosporium by the Canadian mycologistStanley Hughes in 1958; however, the asymmetry and relatively small size of theconidia combined with the tree-like, branched appearance of the asexual reproductive structures suggested it belonged elsewhere.[6][7] In 1976 the fungus was transferred to the genusGeomyces asGeomyces pannorum by Canadian mycologists Lynne Sigler and John William Carmichael.[7]
Geomyces pannorum is a temperate soil fungus often associated with cold temperatures. It has been isolated from Arctic permafrost as well as the soils of Antarctica.[8][9]Geomyces pannorum has also been recovered from glacier bank soils in Kashmir, India, at an elevation of over 3000 metres, where temperatures rarely exceed 10 °C.[10] This species can survive in arctic cryopegs consisting of super-cooled hypersaline liquid water deposits found beneath or within large masses of ice.[11]Geomyces pannorum has also been associated with Antarctic marine macroalgae and deep-sea ecosystems.[12][13] It is one of the most common fungi isolated in these environments, which suggests that they are involved in decomposition and nutrient-cycling in cold marine ecosystems.[12]Geomyces pannorum is tolerant of up to three times the salinity of seawater.[11][14] This fungus maintains cell and membrane function at low temperatures by elevating levels of unsaturated fats and compounds with cryoprotectant properties such as trehalose and various polyols.[11][15][16] The enzyme systems also retain function at low temperature.[8]
Other reported substrates include debris from a coal mine in Canada, frozen leaf litter, meat, cod, gelatin, and flour.[17][18] The species is also known from indoor environments where it has been found growing on damp walls, floors of gymnasiums, and on paper in archives and libraries.[18]Geomyces pannorum has commonly been isolated from the hairs of burrowing mammals,[11] the feathers ofpetrels,skuas, andpenguins,[19] and the exoskeletons of flying arthropods,[20] all of which may contribute to its dispersal.
Colonies ofG. pannorum are yellow-brown in colour, and typically have a granular, powdery texture produced by microscopic, tree-like sporulating structures.[1][21][22] Theconidia of this fungus are small, wedge-shaped with a flat base. They are smooth or slightly rough-walled, and tend to swell slightly during maturation.[2][21][23] Conidia develop at the tips and along the sides of branched, tree-likeconidiophores.[2] The angles of conidiophore branches tend to be less than 90°. The conidia are formed in short chains of two to fourarthroconidia linked together by empty intervening cells.[2][3][22][24] The conidiophores ofG. pannorum have verticils, which resemble branches radiating around a central, perpendicular main branch.[2] The conidiophores and vegetative hyphae ofG. pannorum are hyaline.[25] Members of the genusChrysosporium differ in having larger conidia and acutely branched conidiophores.[26][27]
Geomyces pannorum is a slow-growing psychrophile, exhibiting growth below 0 °C[8][28] to as low as −20 °C.[14][29] Strains recovered from Antarctic cryopegs germinate at −2 °C two to three weeks after inoculation.[30] Grow is typically observed at 25 °C but absent at 37 °C.[2] The fatty acid composition and metabolism of this species changes in response to environmental temperature.[31] As well, cultures isolated from different places exhibit differing morphological characteristics and varying rates of glucose and lipid utilization.[15][30]Geomyces pannorum var.vinaceous grows at 4 °C and uses lipids more readily than glucose, possibly as a means to maintain membrane fluidity under low temperature conditions by increasing the proportion of unsaturated fatty acids.[32] In contrast,G. pannorum var.pannorum grows at 25 °C and exhibits a nutritional preference for glucose.[15]
Strains ofG. pannorum arehalotolerant, moderately cellulolytic, and able to survive and grow in the presence of multiple environmentalstressors.[12][30] This species is generally regarded to be keratinophilic (exhibiting a proclivity to grow on shed keratin)[31] and accordingly produces keratinases.[19][33] Sodium chloride is stimulatory to its growth onCzapek's medium (a growth medium in whichsodium nitrate is the sole source ofnitrogen andsucrose is source ofcarbon).[34] Growth has been observed in low oxygen environments.[34]Geomyces pannorum is resistant to the antifungal agentcycloheximide.[2][3] However the growth of this species is inhibited byultraviolet(UV)-B light.[22][35]
Although mostGeomyces species remain dormant until the introduction into their environment of new organic material,G. pannorum is unique in its ability to grow on silica gel in the absence of organic material.[36] It produces a range of extracellular hydrolases includinglipase, chitinase, andurease.[11] It has been reported as a saprotroph on the colonies of other fungi includingCladosporium sphaerospermum.[37]
Geomyces pannorum is regular contaminant found in cultures of dermatological specimens of humans and domestic animals (dogs, cats, horses).[1][2] It is also encountered in respiratory specimens from humans and animals where its presence is similarly interpreted as clinically insignificant.[22] A case of skin infection over the upper trunk and arms of a healthy, non-immunocompromised man was reported,[38] as was a case of recurrent cutaneousG. pannorum infection was reported in three brothers withichthyosis.[39] However the several cases whereGeomyces pannorum has been implicated in infection are suspected to be erroneous.[1][22]
Fungal18S rDNA fragments ofG. pannorum have been recovered from glass panels of 19th century churches in Brakel, Germany, where their presence was interpreted to contribute to have degradation.[43] Minimal organic films on optical glass provide sufficient nutrition to sustain growth of this species, causing etching of the glass surface.Geomyces pannorum has been implicated in thebiodegradation of buriedplastics such aspolyesterpolyurethane.[44] It is capable of degrading plasticizedpolyvinyl chloride (pPVC) and polyurethane resins.[44][45][46]
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