Fungi: Characteristics, Classification, and Uses
Order of Characters for Identification in Fungi
The following characteristics are used to identify fungi:
- Gross appearance of the colony
- Type of hyphae
- Placement of sporophores
- Presence of sterigmata (sporangiophore or conidiophore) and their order
- Shape, size, and distribution of spores
- Presence or absence of rhizoids. Occur only in non-septate fungal hyphae. For example: Rhizopus, Rhizomucor, Absidia
- Practice biochemical identification tests.
Fungi have been treated as vegetables since ancient times, due to their immobility and the presence of a cell wall, although they are heterotrophic. This means they are unable to fix carbon through photosynthesis, but use carbon fixed by other organisms for metabolism. We now know that fungi are closer to the animal kingdom (Animalia) than the plant kingdom (Plantae) and are located next to the first monophyletic taxon within the group of opisthokonts.
During most of the Paleozoic era, fungi were apparently aquatic. The first terrestrial fungi appeared probably in the Silurian period, just after the appearance of the first land plants, but their fossils are fragmentary. The tallest known fungi evolved 350 million years ago, i.e., in the Devonian period, and were the so-called Protaxites, which reached 6 meters in height. Perhaps the appearance, shortly after, of the first trees caused evolutionary competition that led to the disappearance of higher fungi.
Unlike animals that ingest food, fungi absorb it, and their cells have cell walls. Because of these reasons, these organisms are located in their own biological kingdom, called Fungi.
The fungi form a monophyletic group, which means that all varieties of fungi come from a common ancestor. The monophyletic origin of fungi has been confirmed by multiple molecular phylogeny experiments; shared ancestral traits include chitinous cell walls and heterotrophy by absorption, among other shared characteristics.
The taxonomy of fungi is in a state of rapid change, especially due to recent papers based on DNA comparisons, often translocated assumptions of classification systems. There is no unique system fully accepted at the higher taxonomic levels, and there are constant name changes at every level, from the species level up and, according to the group, also at the species level and below. There are sites like Index Fungorum, ITIS, and Wikispecies recording the updated preferred names (with cross-references to older synonyms), but they do not always agree among themselves or with their names in Wikipedia or in each language variant.
Despite their monophyletic nature, fungi have a remarkable morphological variability, given not only by appearance but also by size and characteristics. Thus, there are fungi like the Protaxites, 6 meters high, as well as molds and yeasts, mushrooms (the name given precisely to macroscopic edible fungi that grow on the ground), underground truffles, or almost microscopic fungi, such as powdery mildew or ringworm or other mycoses (pityriasis, etc.), rust, etc.
The symbiotic association of fungi with algae results in lichens.
Traditional Classification of Fungi
- Amoeboid or slime fungi
- Myxomycetes (division Myxomycota)
- Plasmodiophoromycetes (division Plasmodiophoromycota)
- Lysotrophic or absorbotrophic fungi
- Pseudofungi or oomycetes (division Oomycota)
- Chytrids (division Chytridiomycota)
- True fungi or eumycetes (division Eumycota)
- Zygomycetes (class Zygomycetes)
- Ascomycetes (class Ascomycetes)
- Imperfect fungi (class Deuteromycetes)
- Basidiomycetes (class Basidiomycetes)
The groups of the list above up to Oomycota (included) are not true fungi but protists with different relationships whose adaptations made them confused with fungi.
Current Classification of the Kingdom Fungi (2010)
- Chytridiomycota (division Chytridiomycota)
- Zygomycetes (division Zygomycota)
- Glomeromycetes (division Glomeromycota)
- Basidiomycetes (division Basidiomycota)
- Ascomycetes (division Ascomycota)
Differential Characters
- Cellular level: Eukaryotic
- Nutrition: Osmotrophic (absorption)
- Oxygen metabolism: Aerobic, anaerobic, or facultative
- Reproduction and Development: Sexual reproduction, with generally equal gametes and asexual propagation of resistant spores.
- Organization: The best known are multicellular, with cells in filaments called hyphae, which together form a mycelium. Lack of mobile phases, such as flagellate forms, with the exception of the male gametes and spores of some phylogenetically primitive forms (the Chytridiomycota).
- Structure and functions: No plasmodesmata (cytoplasmic bridges between cells). Unicellular like yeast in beer (Saccharomyces cerevisiae) or multicellular mycelium consisting of hyphae. Intracellular movements. On the walls are porous. Chitin cell wall.
- Morphological characters: The main characters of macroscopic fungi are the fruiting body of mushrooms.
- Detail the mushroom type, umbrella-shaped, with foot and hat.
- Hat: Size, shape, texture, thickness, margin, cuticle, flesh.
- Hymenium: Plates, tubes, pores, spines, folds.
- Foot: Shape, size, color, consistency, ring, volva, curtain, mycelium.
- Spore: Color
- Smell: Anise, bitter almond, garlic, coal gas, ink, phenol, or soap.
- Flavor: Sweet, sour, pungent, bitter
- Habitat: Damp places and in low light.
Function of the Fungal Cell Wall
- Protect the fungus from osmotic lysis and toxic metabolites.
- Having permeability to nutrients, gases, and enzymes
Utility of Fungi
Ornamental Mushrooms
Due to their beauty, many fungi have been used for aesthetic and ornamental purposes, including them in offerings that, together with flowers and branches, are offered at various ceremonies. At present, it is still easy to find this custom in some ethnic groups of Mexico, such as the Nahuatl in the Sierra de Puebla-Tlaxcala; the Zapotec in Oaxaca, and the Tzotzil and Tojolabal in Chiapas. The fungi most commonly used for this purpose are the psychedelic mushrooms Amanita muscaria; the latter has become the stereotype of a mushroom so that it is highly appealing because it is composed of a white thallus and an umbrella (basidiocarp) that is red, speckled with white.
Food Fungi
Perhaps the first direct use given to fungi is food. Much has been discussed on their nutritional value, although most would be considered high quality because they contain a good proportion of protein and vitamins and a low amount of carbohydrates and lipids. Among the most used are: Boletus edulis, Lactarius deliciosus, Russula brevipes, and Amanita caesarea. Other fungi that are consumed significantly are: Agaricus campestris and A. bisporus, in our area commonly known as “mushrooms” or “Paris mushrooms”. The importance of these is because they are among the few species that can be grown artificially and industrially.
Microscopic fungi also contribute directly or indirectly to the creation of food sources and represent an expectation of support for the future in this field. These include the work of production of biomass from yeasts such as Candida utilis, which is used to improve forage food.
The growth of various fungi on some foods can increase their nutritional level. For example, in the states of Tabasco and Chiapas, a fermented drink based on ground corn is consumed, which is popularly known by the name of pozol. There are studies indicating that as the fermentation days increase, so does the mycological content, mainly providing amino acids and proteins.
Fungi Entheogens (Hallucinogens)
Entheogenic fungi are of particular importance in Mesoamerica because they are widely distributed. As with individuals of the genus Claviceps, fungi like the hallucinogenic psilocybin mushrooms have been used recently by the pharmaceutical industry for the removal of psychotherapeutic products (psilocybin and psilocin) and some species of the kingdom Monera. Some fungi are reported as actually toxic entheogens. Magic mushrooms were popularized in the world by researcher Gordon Wasson and the famous Mazatec priestess.
Medicinal Mushrooms
Since Fleming’s discovery of penicillin as a metabolite antagonistic mechanism against fungi with other microorganisms, a large industry has developed for the discovery, separation, and marketing of new antibiotics. Among the most important medicinal species, we can mention Ganoderma lucidum, Trametes versicolor (Coriolus), Agaricus blazei, Cordyceps sinensis, and Grifola frondosa, among many others.
Fungal Contaminants
Fungal contaminants are a serious problem for humans. These include those that parasitize and rot wood, such as Coniophora or those commonly known as “ears”. However, the greatest harm is obtained from microscopic fungi, highlighting the [mold] that can attack and degrade.
Poisonous Mushrooms
In nature, only certain varieties of mushrooms are edible; the rest are toxic. Ingestion may cause severe multisystem damage and even death. Mycology has detailed studies on these varieties of fungi. It is very important to take the above seriously.
Species such as Amanita phalloides, Cortinarius orellanus, Amanita muscaria, Chlorophyllum molybdites, Galerina marginata, or Lepiota helveola have enzymes that are toxic to humans, causing symptoms such as tachycardia, vomiting and cramping pain, cold sweating, excessive thirst, and sudden drops in blood pressure, excretions with blood. The victim contracts severe necrotic lesions in all organs, especially the liver and kidney. This damage is often irreparable and generally requires organ transplantation.
The recognition of these fungi requires acquiring visual recognition of the morphology of poisonous mushrooms. There is no generally valid method for recognition; the only way is to know and recognize them.
As outpatient treatment to apply if you suspect the consumption of poisonous mushrooms, induce immediate expulsion by vomiting in the victim and administer the so-called universal antidote. Take the affected person to medical emergencies within 4 hours of consumption for extremely urgent attention.
Gallery of poisonous mushrooms
Mushroom Cultivation
The cultivation of mushrooms is called mycoculture and is practiced for economic or scientific interest. In the first case, edible species such as Pleurotus or Agaricus or saprotrophic species produce allopathic substances (antibiotics) (such as penicillin, produced by fungi of the Penicillium). Yeasts are important in the production of fermented foods and beverages, especially of the genus Saccharomyces, as well as model organisms in biological research.
It is possible to grow or allow mold to thrive for study at home or at school. On moist bread, the mycelium of Rhizopus soon grows, which has globose, dark sporangia, and on citrus peel, Penicillium develops quickly, with its characteristic blue-green spores. Fungi usually grow best in semi-darkness and wet environments.
However, it is advisable to conduct these studies under the supervision of a mycologist or specialist, as there are highly dangerous molds.