General structures of fungi

• Fungi are eukaryotic organisms that do not contain chlorophyll, but have cell walls, filamentous structures, and produce spores
• Fungi grow as saprophytes and decompose dead organic matter
• There are between 100,000 to 200,000 species of fungi depending on classification, with about 300 species known to be pathogenic for humans
• The oldest undisputed fossils of fungi are about 460 million years old, and fungi were among the earliest colonizers of land, probably as symbionts with early land plants
• Beneficial effects of fungi include decomposition, nutrient and carbon recycling, biosynthetic factories for drugs and food production, and being model organisms for biochemical and genetic studies
• Harmful effects of fungi include the destruction of food, lumber, paper, cloth, animal and human diseases, toxins produced by poisonous mushrooms, and plant diseases
• Fungi reproduce by means of spores, both sexual and asexual, and may have a stable haploid & diploid states like plants
• Fungi are heterotrophic, produce exoenzymes, store food as glycogen, have a unique sterol in their cell membranes called ergosterol, and most have very small nuclei with little repetitive DNA
• Yeast is unicellular, reproduces asexually by budding and sexually by spores, and stores food as glycogen
• Moulds are multicellular fungi with hyphae, septate or nonseptate, hyaline or dematiaceous, and reproduce sexually and asexually
• Hyphae are designed to increase the surface area of fungi and facilitate absorption, may be coenocytic or have septa with pores, and parasitic fungi have modified hyphae called haustoria
• The body of a fungus mainly exists as slender filaments called hyphae, forming long chains of cells joined end-to-end divided by cross-walls (septa)
• Mycelium is an intertwined filamentous mass formed by hyphae, visible to the unaided eye, with vegetative mycelium remaining inside the substrate for nutrition and reproductive mycelium responsible for spore reproduction
• Hyphae grow from their tips, forming mycelium, which is the ecologically active body of fungi
• The ability to synthesize lysine by the α-amino adipic acid is another characteristic of fungi
• Fungi possess the ability to synthesize lysine by the α-amino adipic acid pathway (AAA-pathway) and have a chitinous cell wall, plasma membranes containing the sterol ergosterol, and microtubules composed of tubulin
• The fungal cell wall provides protection against osmotic lysis and can contain pigments like melanin to protect against ultraviolet radiation or lytic enzymes of other organisms
• Cell wall components consist of chitinous microfibrils embedded in a matrix of small polysaccharides, proteins, lipids, inorganic salts, and pigments
• The plasma membrane of fungi regulates the uptake and release of materials, contains integral membrane proteins like chitin synthase and glucan synthase, and differs from mammalian membranes by containing the sterol ergosterol
• Microtubules in fungi, composed of tubulin, are involved in the movement of organelles, chromosomes, nuclei, and Golgi vesicles containing cell wall precursors
• Fungal nuclei are variable in size, shape, and number, with the number of chromosomes varying among different fungi species
• Fungi can reproduce either asexually (imperfect) or sexually (perfect), with asexual reproduction resulting in the formation of conidia following mitosis
• Fungi life cycle stages:

  • Haploid (n)
  • Heterokaryotic (unfused nuclei from different parents)
  • Diploid (2n)
  • Plasmogamy (fusion of cytoplasm)
  • Heterokaryotic stage
  • Karyogamy (fusion of nuclei)
  • Sexual reproduction with spore-producing structures and spores
  • Asexual reproduction with zygote, mycelium, germination, and meiosis
• Sexual life cycle of fungi involves cell fusion, plasmogamy, nuclear fusion, karyogamy, and an intervening heterokaryotic stage
• Asexual reproduction in fungi includes molds like Penicillium that grow on food and yeasts that produce by simple cell division
• Some molds and yeasts have no known sexual stage, traditionally called deuteromycetes or imperfect fungi
• Reproduction in Zygomycetes involves asexual reproduction by production of spores (sporangiospores)
• Specialized structures in vegetative mycelia by certain fungal species include antler, racquet, spiral hyphae, and rhizoid
• Fungal hyphae can be septate (with frequent cross-walls) or sparsely septate (few cross-walls at irregular intervals) or aseptate (absence of septations)
• Identification of fungi based on pigmentation: hyaline hyphae are nonpigmented or lightly pigmented, while dematiaceous hyphae are darkly pigmented due to melanin
• Dimorphism in fungi refers to the ability to exist in two forms depending on growth conditions, like a mould phase and a yeast phase
• Thermally dimorphic fungal species associated with human disease include Blastomyces dermatitidis, Coccidioides immitis, Histoplasma capsulatum var. capsulatum, Paracoccidioides brasiliensis, Sporothrix schenkii, and Penicillium marneffei
• Polymorphic fungi have both yeast and mould forms in the same culture, observed in Exophiala spp., with the yeast phase typically observed initially followed by the mould phase as the colony ages
• Fungi are eukaryotic organisms that do not contain chlorophyll, but have cell walls, filamentous structures, and produce spores
• Fungi grow as saprophytes and decompose dead organic matter
• There are between 100,000 to 200,000 species of fungi depending on classification, with about 300 species known to be pathogenic for humans
• The oldest undisputed fossils of fungi are about 460 million years old, and fungi were among the earliest colonizers of land, probably as symbionts with early land plants
• Beneficial effects of fungi include decomposition, biosynthetic factories for drugs and food production, and being model organisms for studies
• Harmful effects of fungi include destruction of food, lumber, paper, cloth, animal and human diseases, toxins from poisonous mushrooms, and plant diseases
• Fungi reproduce by means of spores, both sexual and asexual, and may have stable haploid and diploid states