Introduction to mycology

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

Fungi Yeasts Mycelial fungi Dimorphic fungi

Yeasts Unicellular fungi Grow by division Budding Binary fission Some times daughter cells may not detach themselves the result is a pseudohyphae Pseudohyphae

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 Non septate hyphae: coenocytic Septa contain pore. All cytoplasm is connected.

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

Dimorphic fungi: Candida albicans

Fungal spores: Vegetative spores Arthrospores, eg, Coccidiodes immitis Chlamydospores, eg, Candida albicans Blastospores, eg, Candida albicans

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

Conidiospores

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

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

Terminology Ascospore: asexual spore produced in a sac-like structure called an ascus Arthospores: asexual spore 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

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