SECTION 2: CLASSIFICATION & FUNGAL STRUCTURES --- Classification by Sexual Reproduction Group Sexual Spore Key Features Examples --- --- --- --- Zygomycetes Zyg
SECTION 2: CLASSIFICATION & FUNGAL STRUCTURES --- Classification by Sexual Reproduction Group Sexual Spore Key Features Examples --- --- --- --- Zygomycetes Zygospores Non-septate hyphae, asexual spores = sporangiospores Rhizopus , Mucor Ascomycetes Ascospores (in asci/sacs) Largest phylum — 60% known fungi, ~85% human pathogens; asexual spores = conidia Candida , Histoplasma , Trichophyton Basidiomycetes Basidiospores (in basidia) Called "club fungi"; fruiting bodies = basidiocarps Cryptococcus neoformans , mushrooms Deuteromycetes None "Fungi Imperfecti" — no sexual stage demonstrated; reclassified when sexual stage discovered Penicillium , Aspergillus Note: The largest phylum is Ascomycota. Remaining pathogenic fungi are zygomycetes or basidiomycetes. --- Classification by Morphology 1. Moulds Filamentous fungi made of cylindrical tube-like structures called hyphae . A mass of hyphae is a mycelium . Examples: Aspergillus spp., Trichophyton rubrum Hyphae are either: - Septate — have cross walls (septa) with small pores through which cytoplasm flows continuously. If damaged, pores can be plugged to prevent death of the whole strand. More evolved. - Aseptate (non-septate) — no septa; more primitive. If damaged, entire strand dies because cytoplasm cannot be contained. - All moulds are septate except Zygomycetes ( Rhizopus , Mucor ) - All fungal hyphae are coenocytic (multinucleate — many nuclei share the same cytoplasm) 2. Yeasts Unicellular fungi, spherical or ellipsoid in shape. Reproduce by budding producing blastospores (blastoconidia) . Examples: Cryptococcus neoformans , Saccharomyces cerevisiae Key points: - When buds fail to detach and elongate, they form pseudohyphae — seen in Candida albicans - C. albicans can also produce true hyphae (germ tube) — important diagnostic feature - True yeasts like S. cerevisiae do NOT produce pseudohyphae - Some yeasts produce a polysaccharide capsule — e.g. Cryptococcus neoformans , yeast form of Blastomyces dermatitidis - Some yeasts are pigmented 3. Yeast-like Are yeasts but produce pseudohyphae. Example: Candida albicans 4. Dimorphic (Diphasic) Exist in two morphological forms depending on environmental conditions and temperature: - Yeast form — found in infected tissue AND in vitro at 37°C - Mould form — found in soil/natural habitat AND in vitro at 25°C (room temperature) Dimorphic fungi of medical importance: - Histoplasma capsulatum - Blastomyces dermatitidis - Paracoccidioides brasiliensis - Coccidioides immitis Memory tip: HBPC — Histo, Blasto, Paracoccidio, Coccidio --- Reproduction in Fungi Asexual Reproduction (by mitosis): Spore Type Description Example --- --- --- Conidia/Conidiospores Small single-celled microconidia OR large multicellular macroconidia formed at hyphal tips Aspergillus , dermatophytes Sporangiospores Single-celled spores inside a sac (sporangium) on a sporangiophore Rhizopus , Mucor Arthrospores Formed from fragmented hyphae Coccidioides immitis Chlamydospores Thick-walled spores; resistant to harsh conditions Candida albicans Blastospores/Blastoconidia Formed by budding process Yeasts Sexual Reproduction (by meiosis): - Compatible nuclei unite within the mycelium → nuclei fuse → diploid nucleus → meiosis → sexual spores - Fungi with known sexual stages = perfect fungi - Fungi without sexual stages = imperfect fungi Sexual Spore Structure Group --- --- --- Ascospores Formed in a sac called an ascus (4–8 per ascus) Ascomycetes Basidiospores Formed in a basidium Basidiomycetes Zygospores Large thick-walled spores; formed when tips of two sexually compatible hyphae fuse Zygomycetes --- Dermatophyte Macroconidia & Microconidia — Comparison Table Genus Macroconidia Microconidia Sites infected --- --- --- --- Microsporum Numerous, thick-walled, rough, spindle-shaped, multicellular Rare Hair, skin; rarely nails Epidermophyton Numerous, smooth-walled, club-shaped, in clusters Absent Skin, nails; rarely hair Trichophyton Rare, thin-walled, smooth, pencil-shaped Abundant Hair, skin, nails --- Phyla Summary Zygomycota - Produce zygospores (sexual) and sporangiospores (asexual) - Non-septate hyphae - Example: Rhizopus stolonifer (bread mould) — anchors to substrate with rhizoids Ascomycota (Sac Fungi) - Produce ascospores in asci (sexual) and conidia (asexual) - Examples include truffles, morels, yeasts - Ergot fungus ( Claviceps purpurea ) infects rye → ergotism - Yeasts used in baking (fermentation), glycerol production Basidiomycota (Club Fungi) - Produce basidiospores in basidia - Fruiting bodies = basidiocarps (typical mushroom) - High in protein, calcium, phosphorus, iron - Medically important: Cryptococcus neoformans (meningitis), Amanita (poisonous) - Other pathogens: Coprinus , Schizophyllum (basidiomycosis); Psilocybe (mushroom poisoning) Deuteromycota (Fungi Imperfecti) - No known sexual cycle - Reclassified when sexual stage is discovered - Penicillium → antibiotics, gourmet cheese - Aspergillus → citric acid, soy sauce, aspergillosis, aflatoxin (carcinogen) ---