Introduction to mycology

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A few of us pay attention to one of the most abundant organisms on the planet – fungi. In national olympiads you quite often can find tasks about fungi, however, in the IBO you may be asked to classify them or choose right answers from multiple choice about they properties as well as reproduction mechanisms and structures.

Fungi are eukaryotic organisms that do not contain chlorophyll, but have cell walls, filamentous structures, and produce spores. These organisms grow as saprophytes and decompose dead organic matter. There are between 100,000 to 200,000 species depending on how they are classified. About 300 species are presently known to be pathogenic for man.
There are five kingdoms of living things. The fungi are in the Kingdom Fungi.
Monera Prokaryocyte Bacteria
Protista Eukaryocyte Protozoa
Fungi Eukaryocyte * Fungi
Plantae Eukaryocyte Plants, Moss
Animalia Eukaryocyte * Arthropods
*This common characteristic is responsible for the therapeutic dilemma in anti-mycotic therapy.
The taxonomy of the Kingdom Fungi is evolving and is controversial. Formerly based on gross and light microscopic morphology, studies of ultra structure, biochemistry and molecular biology provide new evidence on which to base taxonomic positions. Medically important fungi are in four phyla:
  • Ascomycota – Sexual reproduction in a sack called an ascus with the production of ascopspores .
  • Basidiomycota – Sexual reproduction in a sack called a basidium with the production of basidiospores.
    Figure 2. Diagram of the general structure of basidia in gilled mushrooms.
  • Zygomycota – sexual reproduction by gametes and asexual reproduction with the formation of zygospores .
    Figure 3. Zygomycota reproductive stages.
  • Mitosporic Fungi (Fungi Imperfecti) – no recognizable form of sexual reproduction. Includes most pathogenic fungi.
    Figure 4. Freshwater Mitosporic Fungi
    Pathogenic fungi can exist as yeasts or as hyphae (figure 5). A mass of hyphae is called mycelia. Yeasts are unicellular organisms and mycelia are multicellular filamentous structures, constituted by tubular cells with cell walls. The yeasts reproduce by budding. The mycelial forms branch and the pattern of branching is an aid to morphological identification. If the mycelia do not have septa, they are called coenocytic (non-septate). The terms “hypha” and “mycelium” are frequently used interchangeably. Some fungi occur in both the yeast and mycelial forms. These are called dimorphic fungi.

    The dimorphic fungi have two forms (figure 6):

    Dimorphic fungi
  • YEAST – (parasitic or pathogenic form). This is the form usually seen in tissue, in exudates, or if cultured in an incubator at 37 degrees C.
  • MYCELIUM – (saprophytic form). The form observed in nature or when cultured at 25 degrees C. Conversion to the yeast form appears to be essential for pathogenicity. Dimorphic fungi are identified by several morphological or biochemical characteristics, including the appearance of their fruiting bodies. The asexual spores may be large (macroconidia, chlamydospores) or small (microconidia, blastospores, arthroconidia).

Then read this.

Also, take a look at this quick review about mycology.

Next, a good video to summarize what you’ve learned.

Lastly, a brief video below about fungi.

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