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Introduction to mycology

Introduction to mycology. Fungi-Eucaryotes. Eucaryotic cells with characteristic organelles Thick cell wall, mostly carbohydrate Cellulose or chitin most common components No chloroplasts Metabolically very similar, distinguished by morphology 3 main types Yeasts Filamentous fungi

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Introduction to mycology

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  1. Introduction to mycology

  2. Fungi-Eucaryotes • Eucaryotic cells with characteristic organelles • Thick cell wall, mostly carbohydrate • Cellulose or chitin most common components • No chloroplasts • Metabolically very similar, distinguished by morphology • 3 main types • Yeasts • Filamentous fungi • Dimorphic fungi

  3. Fungi • Yeasts • Dimorphic fungi • Mycelial fungi

  4. Yeasts • Unicellular fungi • Grow by division • Budding • Binary fission • Sometimes daughter cells may not detach themselves the result is a pseudohyphae Pseudohyphae

  5. Filamentous fungi (molds) • Multicellular, multinucleate • Basic unit is the hyphae, a long thin filament • Hyphae branch and cross link to form a mat (mycelium) • Growth occurs at hyphal tip • Hyphae may be divided by cross-walls (septa) into uninuclear units • Septa contain pore. All cytoplasm is connected. • Non septate hyphae: coenocytic

  6. Mucor

  7. Dimorphic fungi • Fungi able to switch between growth as a mycelium and a yeast • Depends on environmental conditions • Usually one form is pathogenic and the other is saprophytic • Most cases yeast form is pathogenic, eg, Histoplasma capsulatum • In some cases hyphal form is pathogenic, eg, Candida albicans Histoplasma Candida albicans

  8. Fungal spores: Vegetative spores • Arthrospores, eg, Coccidiodes immitis • formed by the disarticulation of the mycelium • Chlamydospores, eg, Candida albicans • thick-walled, resistant spores formed by the direct differentiation of hyphae • Blastospores, eg, Candida albicans • formed by budding from the ends or sides of the parent cell

  9. Fungal spores: Asexual spores • Some hyphae grow up from the mycelium and differentiate to produce spores • The most important of these are conidiospores • The hyphae develops to produce a specialised spore producing body called the conidiophore • Some fungi produce large conidia containing multinucleate spores (macroconidia) and small conidia which produce unicellular spores (microconidia)

  10. Conidiospores

  11. Sexual Spores • Zygospores: When two hyphae of suitable mating strains come into contact each produces a short side branch, the distal part of which becomes filled with dense protoplasm and is cut off by a transverse wall to form the gametangium. • Oospores are characteristic of the more primitive Phycomycetes. The male gamete reaches the oosphere (egg) through a germ tube. • Ascospore: produced in a sac-like structure called an ascus

  12. Pathogenic mechanisms - Fungi • Invasiveness: multiply in skin and keratin producing common superficial infection (Ringworm, athletes foot) • Fungi gaining access to tissue cause subcutaneous infections • In the blood they cause life threatening systemic infections in the immunocompromised • Toxin production: ingestion of mouldy food in which fungal metabolites have been produced causes poisoning • Allergic reactions: inhalation of fungal hyphae or spores causes hypersensitivity reactions

  13. Cultivation of fungi • Fungi are chemoheterotrophs • Growth requirements similar to bacteria some require complex substances such as keratin • Optimum growth temperature for many fungi much lower than for pathogenic bacteria • Most fungi grow at lower pH than bacteria • Media • Sabourauds agar • Dextrose and peptone, pH5.6 • Yeast grow as colonies • Filamentous fungi grow as a mycelium

  14. Terminology • Ascospore: produced in a sac-like structure called an ascus • Arthospores: formed by the disarticulation of the mycelium • Blastospores are formed by budding from the ends or sides of the parent cell, e.g., the yeast, Candida • Chlamydospores: thick-walled, resistant spores formed by the direct differentiation of hyphae • Conidia: asexual spore formed from hyphae by budding or septal division

  15. Terminology • Conidiophore: a stalk-like branch from the mycelium in which conidia develop either singly or in numbers • Germ tubes: tube-like structures produced by germinating spores • Hyphae: the filaments that composed the body of a fungus • Macroconidia: large multinucleate spores • Microconidia: single-celled spores • Mycelium: a mat made up of interwining thread-like hyphae • Pseudohyphae: filaments composed of elongated budding cells that have failed to detach

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