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Rhinocladiella atrovirens
Rhinocladiella atrovirens is a fungus of the genus Rhinicladiella, and is generally classified as a dematiaceous (dark-walled) fungus in the family Herpotrichiellaceae. It occurs naturally on rotten wood and was first isolated from pine wood in Sweden in 1933. It also colonizes sapwood of Japanese red pine logs. Apart from conifer wood, this species is also known from honey, insulation material, Pinus contorta, Pinus radiata, Thuja plicata, gymnosperm wood, stem of Lunaria annua, sewage, and a door post.

Morphology is poorly developed in the black yeast-like fungi; when present, phylogenetically remote species express very similar microscopic structures.

=Morphology= The colonies formed by Rhinocladiella atrovirens are restricted, olivaceous, velvety or lanose. The center of the colony is often slightly mucoid at the center. In terms of colour, the submerged hyphae are hyaline to pale oliveaceous; aerial hyphae are reverse dark olivaceous green to blackish.

The conidiophore stalks of Rhinocladiella atrovirens are short, pale to dark brown, and thick-walled. They are slightly differentiated, suberect, usually branched, and have denticles.

Conidia, formed on the elongating conidiophore, are unicellular, smooth- and thin-walled, short, and cylindrical. They are broadly ellipsoidal and range from 3.7-5.5 x 1.2-1.8 µm in size, whereas condiogeneous cells are cylindrical, intercalary or free, and range from 9-19 x 1.6-2.2 8 µm in size. The conidia may grow either as a single bud or in short chains with truncated basal scars. Germinating cells appear to be inflated and spherical to subspherical.

=Similarity to other species= Rhinocladiella atrovirens has been found to be pleomorphic, meaning it has more than one conidial state. This immense variability in its conidiogenesis has created a great deal of taxonomic confusion. They display both a sympodial and annellidic mode of growth; despite the fact that the former is predominant, the two types of conidiation have been observed to be located on a single hypha previously. Although Rhinocladiella atrovirens was originally characterized by the production of a single conidium at the apex of the sympodial conidiogenous cell, it is now known that the sympodial conidiophore tends to resume growth post-sporulating; it will often sporulate again at the denticles of the new apex, which is a differentiating factor for this species. The conidia may also be located along the sides of conidiophores.

The initial conidia growth occasionally gives rise to secondary conida, allowing potential confusion with Fonsecaea pedrosoi. A factor that allows for distinguishing between Fonsecaea pedrosoi and Rhinocladiella atrovirens is that there is often an annellated yeast (Phaeoannellomyces elegans) synanamorph inconspicuously present with Rhinocladiella atrovirens. A synanamorph of the Phialophora genus may also occur, albeit, rarely.

Species belonging to Rhinocladiella such as Rhinocladiella atrovirens may also be confused with species of belonging to the Ramichloridium genus. The main feature to distinguish the two similar genus is the presence of annellidic exophiala-type budding cells in Rhinocladiella.

=Reproduction= The sexual or telemorph state of the Rhinocladiella genus reproduction has not been observed, and thus, Rhinocladiella atrovirens belongs to the group that produces their spores asexually, Fungi Imperfecti.

=Pathogenesis= Like other black molds Rhinocladiella, are considered fungi of low virulence, as they can persist in skin tissue of hosts that are not immunocompromised for months to years without propagating to other organs. Few previous reports exist of the culture of Rhinocladiella atrovirens from human sources, although the species has been isolated from clinical specimens from the cornea and sputum thus far. Although Rhinocladiella atrovirens is considered to be low in virulence, a number of dematiaceous fungi have been reported to be neurotropic pathogens. For example, Rhinocladiella atrovirens has been shown to invade the central nervous system of an AIDS patient, cause mycetoma of the foot , and chromoblastomycosis. In the case of the central nervous system infection of the AIDS patient, the patient developed night sweats, fever, and oral and esophageal candidosis. His neurological symptoms worsened with time, despite broad antifungal treatment, eventually resulting in a deep coma, and eventually, death.

=Treatment= Rhinocladiella atrovirens is currently susceptible to the antifungals Amphotericin B, Itraconazole, and Voriconazole, but is resistant to Benomyl (Benlate).

=Laboratory Precautions= It is a biosafety level 1 (BSL-1) organism, meaning there is minimal potential hazard.