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The below mentioned article provides a study note on Fungi.
Meaning of Fungi:
Fungi (Lat. fungus—mushroom) are eukaryotes with a distinct nucleus and rigid chitinous cell wall and were formerly regarded as plants without chlorophyll and are now grouped with protozoa slime moulds and most algae as Higher Prostita. Mycoses are infections caused by true fungi.
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Eumycetes contains more than 80,000 species and can be classified morphologically into:
(1) Phycomycetes:
They are fungi with an unicellular, non-septate mycelium (500 species). The spores (endospores) are enclosed in special sporangia. Reproduction is sexual and asexual. Atypical representative of Mucor (bread mould) is Mucor mucedo. Pathogenic species of this Mucor (mould) may cause infection of lungs, middle ear and general severe infectious process in man.
The mould (filamentous) or mycelial fungi grow as long filaments (hyphae) and reproduce by formation of spores. The major part of the mycelium the vegetative mycelium grows and penetrates into the substrate absorbing nutrients for growth; other hyphae form aerial mycelium and protrude from the vegetative mycelium into the air. They form various kinds of spores and disseminate them in the air.
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(2) Ascomycetes:
Ascomycetes of sac fungi (35,000 species) have a multicellular mycelium. They reproduce sexually by means of ascospores (spores which develop in spherical spore cases), asci—ascus (Gr. askos—sac) and asexually by conidia (exospores which have the function of asexual reproduction in many fungi).
The genus Aspergillus belongs to the class Ascomycetes. These fungi have divided separate mycelium and an unicellular conidiophore which terminates in a fan-like row of short sterigmata from which the spores are pinched off in chains-conidia (Gr. konia—dust).
The fruiting part of the aspergillus resembles a jet of water from a watering can and hence the name “Sprinkler” mould. Aspergillus niger is a representative of Aspergilla and is widespread in nature, certain species may cause aspergillosis of the lungs, ear and eye of man and may infect the whole body.
The genus Penicillium belongs to the class Ascomycetes. The mycelium and conidiophore are multicellular. The fruiting body is in the shape of a brush. The conidiophore branches towards its upper part and terminates into sterigmata from which even-rowed chains of conidia are pinched off (Fig. 99.1).
This genus of fungi is widespread in nature (fodder, milk products, moist objects, old leather, ink, jam). The type species is Penicillium glaucum. Certain species (Penicillium notatum, Penicillium chrysogenum) are used for the production of penicillin which is widely used in the treatment of many infectious diseases.
Some species of this genus of fungi are pathogenic and cause infection of the skin, nails, upper respiratory tract, lungs and other organs of man.
Yeasts belong to the class Ascomycetes. They are large, oval, round, rod shaped cells. They have a double cell wall and well defined nucleus. The cytoplasm is homogeneous—sometimes of a fine granular structure. It contains inclusions (glycogen, volutin, lipid) and also filamentous bodies-chondriosomes which are responsible for synthetic process of the cell.
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Yeasts multiply by budding, fission, sporulation and some of them reproduces asexually. Daughter cells produced by budding from the parent cell transform into independent individuals. The yeasts can also reproduce by sporulation. When there is lack of nutrition, 2, 4, 8 or 16 endospores are formed inside the cells of some species of yeast.
Yeast cell forming the ascospores is called the ascus (sac), while sporulating yeasts are known as Ascomycetes, since the yeasts ferment various carbohydrates, they are widely used in brewing beer, in wine making and in baking bread. Saccharomyces cerevisiae, S. elipsoides are typical representatives of the yeasts.
Among the asporogenic yeasts (family Saccharomycetaceae), there are species pathogenic to man; they are called as Candida (Fig. 99.4) which cause grave disease known as candidiasis. They occur as a result of the growth inhibition of the normal micro flora by antibiotics used for treating a number of infectious diseases and inflammatory processes.
(3) Basidiomycetes:
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Fungi with a multicellular mycelium. These organisms predominantly reproduce asexually by basidiospores (basidia reproductive organs) in which a certain number of spores develop, usually 4. Certain species are free parasites. Two hundred species of mushrooms are used as food. Twenty-five species of mushrooms are poisonous.
Smut fungi invade grains crops causing disease known as smut. Rust fungi affect sunflowers and other plants producing orange coloured spots on infected plants. Imperfect fungi (Fungi imperfecti) are a rather large group of fungi consisting of a multicellular mycelium without either asco- or basidiosporangiophore, but only with conidia.
Reproduction is asexual; but the sexual reproduction is unknown. To this class belong the orders Hyphomycetes, Melanconiales and Sphaeropsidales.
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Among the hyphomycetes, which may be of great interest to the physicians are:
Fusarium graminearum causing intoxication in human (drunken bread), and Fusarium sporotrichioides causing intoxication in man and domestic animals who had eaten the grain crops which had remained in the fields during the winter.
Pathogenic species of imperfect fungi are causative agents of dermatomycoses (superficial mycoses):
Favus (Achorion schoenleini); trichophytosis (Trichophyton violaceum), microsporosis (Microsporum lanosum), epidermophytosis (Epidermophyton inguinale).
