Mycology: historical aspects, general characteristics, classification, reproduction, and main fungal diseases. 1. HISTORICAL ASPECTS Mycology is...

Mycology: historical aspects, general characteristics, classification, reproduction, and main fungal diseases.

1. HISTORICAL ASPECTS

Mycology is a branch of biology dedicated to the study of fungi. The fungi belong to a separate kingdom (Kingdom Fungi), and it is the role of mycology to study all the characteristics of these organisms, including their genetic and biochemical properties, taxonomy, and their use for humans. Fungi are eukaryotic organisms, with only one nucleus, and can be unicellular (yeasts) and multicellular (mushrooms). They are also heterotrophic beings, that is, they do not synthesize their own food. Thus, fungi are considered as great decomposing agents, called saprophytic agents (promote the renewal of organic matter). Experts say that about 1.5 million species of fungi inhabit planet Earth, such as mushrooms, yeasts, molds, and are used for various purposes: culinary, medicine, household products.

Figura 1- Representation of the various types of fungi.

2. GENERAL CHARACTERISTICS OF FUNGI

Fungi are eukaryotic organisms that do not contain chlorophyll, but have a cell wall, filamentous structures, and produce spores. These organisms grow as saprophytes and decompose organic matter. There are between 100,000 to 200,000 species of fungi, varying according to the classification used. About 300 species are currently recognized as pathogenic to humans.

Habitat: Fungi have various types of habitat since they are found in soil, water, plants, animals, humans, and debris in general.

MAIN CHARACTERISTICS OF FUNGI

• Eukaryotes
• Metabolism: heterotrophic
• Saprophytic or Parasitic
• Unicellular and Multicellular
• Chitin cell wall
• Energy reserve (glycogen)
• Achlorophyllous
• Can be aerobic, anaerobic, and facultative anaerobic
• Develop in humid and warm places

3. MORPHOLOGY OF FUNGI

Pathogenic fungi can exist as yeasts or as hyphae. A mass of hyphae is called mycelium. Yeasts are unicellular microorganisms and mycelia are multicellular filamentous structures made up of tubular cells with a cell wall. Yeasts reproduce by budding or fission. The mycelial forms branch and their branching pattern helps with morphological identification. If the mycelium is not septate, it is called coenocytic (non-septate). The terms "hypha" and "mycelium" are commonly used interchangeably. Some fungi occur in both yeast and mycelial forms. These are called dimorphic fungi. Fungi can be morphologically classified in 2 ways: Filamentous Fungi and Yeasts. Dimorphic fungi can have two forms:

• YEAST - (parasitic or pathogenic form). This form is usually found in tissues, exudates, or if grown in an incubator at 37 degrees C.

Figure 2- Microscopic and representative images of yeast cells.

• MYCELIUM - (saprophytic form). Form observed in nature or when cultivated at 25 degrees C. The conversion to the yeast form seems to be essential for pathogenicity. Dimorphic fungi are identified by various morphological or biochemical characteristics, including the appearance of their fruiting bodies. Asexual spores can be large (macroconidia, chlamydospores) or small (microconidia, blastospores, arthroconidia).

Figure 3- Microscopic and representative images of mycelia.

4. FUNGAL REPRODUCTION

ASEXUAL REPRODUCTION

Asexual reproduction in fungi can occur in three ways, by fragmentation, budding, and sporulation.

Fragmentation is a very simple type of asexual reproduction that occurs in certain species of fungi. In this type of reproduction, the mycelium (set of hyphae) breaks, thanks to biotic or abiotic factors, giving rise to clones.

Figure 4- Fragmentation reproduction scheme of mycelia.

*The MYCELIUM is formed by a set of Hyphae - Filamentous Fungi
Hyphae can be septate and non-septate (coenocytic).

Figure 5- Illustrative image of the types of hyphae.