Introduction to mycology

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Introduction to mycology
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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

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Fungi

• Yeasts

• Dimorphic fungi

• Mycelial fungi

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Yeasts

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

Pseudohyphae
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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

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Mucor
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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
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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

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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)

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Conidiospores
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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

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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

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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

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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

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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