Taxonomic Features
The group Deuteromycota is a formal (artificial) taxon. The main criterion for inclusion in this group is the absence of a sexual mode of reproduction. The term "formal" emphasizes that a sexual stage (teleomorph) potentially exists for these microorganisms, but has not yet been discovered.
In modern mycology, the term "mitosporic fungi" is increasingly proposed to replace the classical term "deuteromycetes." It more accurately reflects their mechanism of reproduction: the formation of asexual spores occurs exclusively through mitosis.
If a sexual process is unexpectedly discovered in a fungus from this group during research, its taxonomic status changes. The microorganism is removed from Deuteromycota and reassigned to another phylum—most often Ascomycota (ascomycetes) or Basidiomycota (basidiomycetes). At the same time, the fungus is assigned a new species name corresponding to its discovered teleomorphic (sexual) form.
Morphology and Major Groups
A common morphological feature of most deuteromycetes is the presence of a septate mycelium (divided by cross-walls). They reproduce exclusively asexually by forming specialized structures called conidia.
Within this artificial group, several important categories are distinguished:
- Imperfect yeasts. These include the genera Candida, Cryptococcus, and Malassezia.
- Mould fungi. Represented by the genera Epidermophyton, Coccidioides, Sporothrix, as well as the asexual stage of fungi of the genus Aspergillus.
- Dematiaceous fungi. These are dark-pigmented fungi, such as Phialophora and Fonsecaea.
Representatives of these groups cause numerous human diseases, including various mycoses, mycetoma, phaeohyphomycosis, and chromoblastomycosis.
Characteristics of Imperfect Yeasts (Using Candida as an Example)
The genus Candida is a classic representative of imperfect yeasts (yeast-like fungi). They are the causative agents of candidiasis—an infectious affliction of the skin, mucous membranes, and internal organs.
Cells of the genus Candida are oval in shape, with a diameter varying between 2–5 µm. The primary mode of reproduction is budding.
Key structural features of the genus Candida:
- Formation of pseudomycelium (pseudohyphe). During budding, chains of elongated cells are formed. Unlike true mycelium, they lack a shared outer wall.
- Capacity for dimorphism. Under certain conditions, they can form true septate hyphae.
- Formation of blastospores. Fungi form clusters of budding cells (blastospores).
An important aspect of differential diagnosis: true yeasts (belonging to ascomycetes) are capable of forming ascospores (sexual spores). Yeast-like fungi of the genus Candida never form ascospores. A specific species feature of the pathogen Candida albicans is the ability to form chlamydospores—specific thick-walled resting spores resistant to adverse conditions.