Uncinocarpus Reesii

''Uncinocarpus reesii'' is a species of saprotrophic micro fungi that grows in soil and on keratinous materials such as hair, feathers and skin. It was the first species to be designated as part of the genus ''Uncinocarpus'', owing in part to its characteristic development of hooked (uncinate) appendages. As the closest non-pathogenic relative of '' Coccidioides immitis'' and '' C. posadasii'', it has become a subject of research interest.

History and taxonomy

''Uncinocarpus reesii'' was first recognized under the name ''Gymnoascus uncinatus'' by German taxonomist Michael Emil Eduard Eidam in 1893. The species is named after Robert Rees, an Australian mycologist who provided isolates of ''G. uncinatus'' to Lynne Sigler and G.F. Orr, who in 1976 proposed the re-designation of this species as the first a new genus: ''Uncinocarpus''. This redesignation was based largely in part due to the species' characteristic development of hooked and spiralling appendages, which were not present in any other species of ''Gymnoascus''. Since becoming the first species of the genus ''Uncinocarpus'', others have joined it, including ''U. uncinatus'' and ''U. orissi''. After the advent of high-throughput gene sequencing in the 1990s, genomic studies provided evidence demonstrating that ''U. reesii'' was the closest known non-pathogenic relative of '' Coccidioides immitis'' and '' C. posadasii'', marking the point of divergence from which the pathogenic highly pathogenic Onygenaceae evolved.

Growth and morphology

In culture, colonies of ''U. reesii'' grow moderately fast and are yellowish-white to buff in colour, are flat and dense in shape, and range from velvety to powdery in texture. Arthroconidia of ''U. reesii'' tend to be broad compared to most ''Malbranchea'', ranging from approximately 2.5-3.5 μm x 3.5-6 μm in size. As a heterothallic species, two compatible "sexes" are required for sexual reproduction to occur.

As with other members of the genus ''Uncinocarpus'', ''U. reesii'' can develop hooked (uncinate) appendages on vegetative hyphae. These appendages are short and rigid, with thick walls approximately 8.8μm in diameter. Appendage length rarely exceeds the diameter of the fruiting body (ascocarp). These appendages are found in the asexual stage as extensions of vegetative hyphae, but only develop fertile spore-bearing structures (gymnothecia) in the sexual morph when compatible strains are mated. The gymnothecia are reddish-brown, initially formed on short, bulbous stalks before becoming more or less spherical. The ascospores are smooth, oblate and hole-filled (punctate). When the asexual morph of ''U. reesii'' develops these hooked appendages, they are referred to as "pseudogymnothecia", due to their similar appearance but lack of a spore-bearing structure. In lieu of spores, the asexual form produces arthroconidia that are cylindrical shaped with flattened ends.

Physiology

''Uncinocarpus reesii'' is capable of growing on many different amino acids, but comparatively fewer carbohydrates. In general, growth substrates with a high protein content are most conducive to its growth. ''U. reesii'' is capable of digesting keratin, and grows well in soil rich in animal matter, such as skin and hair. Though less commonly observed, ''U. reesii'' can survive, at least transiently, in human and animal tissue. Its growth is strongly to moderately inhibited at 37 °C.

''Uncinocarpus reesii'' is also capable of digesting cellulose, basic plant sugars and cell wall components, allowing it to degrade plant materials in the surrounding soil. Though ''U. reesii'' can digest both protein and animal matter, its superior growth on high protein substances has led researchers to suggest that this ability to transfer from soil to living host gave rise to the ability of its descendants in the family Onygenales to colonize animals and cause disease.

Habitat and pathogenicity

In the natural environment, ''U. reesii'' is commonly found growing in soil and on keratinous materials, and is found over a wide geographic range. Though there are no recorded cases of disease caused by ''U. reesii'', there is evidence to support the hypothesis that the species is the root of the evolutionary branch from which pathogenic species in the Onygenales arose. The ability of ''U. reesii'' to shift from plant to animal substrates are theorized to have led to development of pathogenicity in several '' Coccidioides'' and ''Paracoccidioides'' species, both of which are highly genetically similar to ''U. reesii''. Another related ''Uncinocarpus'' species, ''U. orissi'', has been implicated in one deep skin infection and two pulmonary infections of humans.

References

{{Taxonbar, from=Q10709291

Onygenales
Fungi described in 1976
Fungus species