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Introduction to mycology

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Title: Introduction to mycology


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
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10
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)

11
Conidiospores
12
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

13
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

14
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

15
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

16
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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