Petriella setifera is a fungus commonly found in soil and feces. The fungus has also been located on wood rot, plant species, and compost. A significant portion of P. setifera reports are found on sources with no previous association with the fungus. There are no known human cases of fungal infection, but one reported case of a dolphin infection. The fungus may have immunosuppressive characteristics, but it has not been confirmed. Many properties of the fungus are unknown, requiring further research.
History and taxonomy
Petriella setifera was first discovered on horse dung by A. Schmidt in Germany 1912. In this discovery, the fungus was categorized as a species of Microascus. It was later determined as a wood fungus by L. Shigo in 1957 when it was collected from a wilted oak tree in West Virginia. Since the discovery, the fungus was found in a variety of environments including wood and soil areas. This fungus was renamed under the genus Petriella in 1930 for reasons currently unknown. Further analysis of the fungus concluded there are multiple stages of development, including Schmidt`s discovery of the fungus in teleomorph phase. In 1961 Barron reported on the Sporotrichum and Graphium anamorph stages of the fungus in isolations from soil. A year later, A.L Shigoon reported the fungus in Tokyo and other regions of the globe including the United States. The fungus continues to be found in other regions, classified under P. setifera.
Morphology and physiology
All species in the genus Petriella have a Graphium state, characterized by dark synnemata and round, single-celled spores in the mucus. Dimorphic pore openings produce condia to form mucoid balls at the synnemata apex, which is similarly found in Lectographium lundbergii. The spores are sexual, non-motile conidiophores. The perithecium in which the sexual spores are borne is pale to dark brown colour, 75-125μm in diameter with scattered hairs along the neck. It is thought that expression of the slime-spored Graphium may be induced by certain environmental conditions.
In the laboratory, asymmetric ascospores were found at room temperature when the fungus was grown on a PDA plate. Clusters of brown-grey chlamydospores have been isolated on the agar. These spores were only found in P. boulangeri previously, but it is believed P. setifera developed chlamydospores to survive in the soil. The asymmetrical ascospore convex and marked germinal pores are unique to P. setifera. The Graphium stage has been associated with fungal reproduction, while the Sporotrichum state has the largest growth and branching. Hyphae are found to form many condia near the apical end during the Sporotrichum stage. CMCase which is also known as cellulase, can be produced by P. setifera optimally at 55 °C and a pH 6.0. The fungus is stable between pH 5.0-8.0 and at temperatures below 45 °C. In-vitro CMCase production has been linked to increased Na+, K+, Ca2+, Mg2+, EDTA and Mn2+ levels in the agar and a severe decrease in Fe2+, Pb2+, Al3+, Zn2+, Fe3+ and Cu2+.
Pathology and medical uses
A single case of infection has been reported from a bottlenose dolphin. Petriella setifera has no known infectious properties for humans or other species. Petriella strains have rarely been associated with vertebrate infections. However, all species in the genus have not been fully analyzed for pathology.
The fungus is known to have antifungal properties. Ethyl acetate extracts from the fungus show activity against fungal pathogens of plants including Magnaporthe grisea and Fusarium oxysporum. The fungus also showed inhibitory effects on Staphylococcus aureus. In-vitro, species of Petriella can produce immunosuppressive metabolites but none of the members of this group are regularly implicated in human disease.