Microascus brevicaulis is a microfungus in the Ascomycota. It is the teleomorph form of Scopulariopsis brevicaulis. Microascus brevicaulis occurs world-wide as a saprotroph in soil, a common agent of biodeterioration, an irregular plant pathogen, and an occasional agent of human nail infection.
Name
Most of the discussion of this fungus in the scientific and medical literature has referred to the fungus using the name of its asexual form, or anamorph, Scopulariopsis brevicaulis. However, a sexual form (teleomorph) named Microascus brevicaulis was recently described. Under the current revision of International Code of Nomenclature for Algae, Fungi, and Plants, as articulated in the Shenzhen Code 2018, it remains unclear which name this fungus will ultimately take. Until further clarification, Microascus brevicaulis is considered the most recent, accepted name.
Bartolomeo Gosio discovered in 1890 that under wet conditions M. brevicaulis produces significant amounts of trimethylarsine via biomethylation of inorganic pigments especially Paris green or Scheele's Green used in indoor wallpapers which is then released into the air.
Morphology
Microascus brevicaulis is a common mold. When cultured at a temperature of 25 °C on potato dextrose agar it forms white colonies which become powdery and/or granular as they mature. Under such conditions the fungus can grow rapidly, expanding as much as 4.5 - 5.5 cm within one week. The hyphae of M. brevicaulis are hyaline (transparent) and septate (separated into segments by cross-walls). The anamorph has conidia that are flattened on the base and tapered at the apex, resembling a boat keel in cross-section or a pontifical mitre. The conidia are produced in chains from cells known as annelides, phialide-like cells that elongate with each successive conidium produced. These, in turn, range from solitary to arranged in complex broom-like clusters on fertile hyphae known as conidiophores. The fungus is a typical perithecial member of Phylum Ascomycota, producing minute, enclosed fruiting bodies containing sexual spores (ascospores) in sacs known as asci. The ascospores of M. brevicaulis are kidney-shaped and reddish-brown in colour.
Ecology
This fungus usually occurs as a mold present in numerous different types of soil as well as various decaying types of organic matter. Microascus brevicaulis has a world-wide distribution, and occurs chiefly as a soil saprotroph. The species is also encountered with some frequency as a non-dermatophyte agent of nail infections (onychomycosis), particularly in toenails. Besides the typical soil life of a decomposer, this fungus is also known to live within the American dog tick, Dermacentor variabilis. This relationship seems to be highly adapted but not as a classic host-parasite interaction. Studies have shown M. brevicaulis inhabits its host as an endosymbiont, and may provides protection against the insect-pathogenic fungus, Metarhizium anisopliae.