LAB - MYCOLOGY

• Mycology


  Study of fungi
• Groups of fungi

  • Macroscopic fungi (mushroom, puffballs, gill fungi)
  • Microscopic fungi (molds and yeast)
• Most fungi are either unicellular or colonial
• In the past mycology was regarded as a branch of botany, although it is now known that fungi are genetically more closely related to animals than to plants
• Fungus


  Any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as mushrooms. Classified as a kingdom, separately from the other eukaryotic kingdoms.
• Characteristics of fungi

  • A characteristic that places fungi in a different kingdom is chitin in their cell walls
  • Fungi, like animals, are heterotrophs; they acquire their food by absorbing dissolved molecules, typically by secreting digestive enzymes into their environment
  • Fungi do not photosynthesize
  • Growth is their means of mobility, except for spores (a few of which are flagellated), which may travel through the air or water
• Approximately 100,000 fungal species have been described, and as many as 1.5 million species may exist
• Fungi form a phylogenetic cluster distinct from other protists and are the microbial group most closely related to animals
• Most fungal species are microscopic and terrestrial
• Metabolic properties of fungi

  • Achlorophyllous (lack chlorophyll pigments and incapable of photosynthesis)
  • Chemoheterotrophic, aerobe, or facultative anaerobe
  • Saprophytic (nutrients are derived from decaying matter and acquired via simple absorption)
• Heterotrophic


  Acquire nutrients from a wide variety of organic substrates
• Saprophytic


  Acquire nutrients from the remnants of dead plants and animals in soil or aquatic habitats
• Parasitic


  Grow on the bodies of living animals or plants, although very few require a living host
• Hyphae


  Found in most multicellular fungi. Network of filaments from which asexual spores are produced. Tubular cell walls that surround the cytoplasmic membrane. Often septate, with cross-walls dividing each hypha into separate cells. Each hyphal filament grows mainly at the tip by extension of the terminal cell.
• Types of hyphae

  • Aerial or reproductive hyphae (stolon) - horizontal filaments that connects sporangiophores or conidiophores together
  • Vegetative hyphae (rhizoids) - root-like, small branching hyphae that grow downwards from the stolons that anchor the fungus to the substrate, where they release digestive enzymes and absorb digested organic material
• Yeasts


  Single-celled fungi. Most of which are in the phylum Ascomycota. Found worldwide in soils and on plant surfaces and are especially abundant in sugary mediums such as flower nectar and fruits. Commonly used in the production of bread, beer, and wine are selected strains of Saccharomyces cerevisiae. Dangerous pathogens: Candida albicans, Histoplasma, and Blastomyces.
• Pseudohyphae


  Formed by a wide variety of yeast species including most pathogenic Candida species and many pleiomorphic fungi that exhibit transitions between filamentous and unicellular forms of growth. Consist of chains of cells, with various degrees of elongation, but still show a constriction between adjacent cellular compartments. Form during the cell division and newly divided cells through budding remain adhered as chains and branches.
• Components of fungal cell wall

  • Chitin (polymer of N-acetyl-glucosamine) arranged in microfibrillar bundles to form a thick, tough wall structure
  • Beta-glucan (site of action of some antifungal drugs)
  • Mannans (gives porosity to cells)
  • Melanin (brown to black pigment)
• Cell membrane


  Made up of ergosterol
• Symbiotic associations between fungi and plants

  • Mycorrhizae - symbiotic associations with the plant roots. Establish close physical contact with the roots. Help the plant obtain phosphate and other minerals and also water from the soil. Fungi obtain nutrients such as sugars from the plant root.
  • Ectomycorrhizae - basidiomycetes and the roots of woody plants
  • Endomycorrhizae - glomeromycete fungi and many nonwoody plants
• Lichens


  Plantlike organisms that consist of a symbiotic association of algae or cyanobacteria and fungi (mostly ascomycetes and basidiomycetes). The photosynthetic algae or cyanobacteria form simple carbohydrates that, when excreted, are absorbed by fungi cells and transformed into a different carbohydrate. Fungi contribute by absorbing water vapour from the air and by providing much-needed shade for the light-sensitive algae beneath.
• Nearly 300 species of fungi can cause human disease
• Types of fungal disease in humans

  • Community-acquired infections caused by environmental pathogens
  • Hospital-associated infections caused by fungal pathogens in clinical settings
  • Opportunistic infections caused by low-virulence species infecting already-weakened individuals
• Most common fungal diseases

  • Fungal nail infections
  • Vaginal candidiasis
  • Ringworm
  • Candida infections of the mouth, throat, and esophagus
• Fungal diseases that affect people who live in or travel to certain areas

  • Blastomycosis - lives in moist soil in parts of the United States and Canada
  • Cryptococcus gattii infection - lives in tropical and subtropical areas of the world, the United States Pacific Northwest, and British Columbia
  • Paracoccidioidomycosis - lives in parts of Central and South America and most often affects men who work outdoors in rural areas
  • Coccidioidomycosis (Valley Fever) - lives in the southwestern United States and parts of Mexico and Central and South America
  • Histoplasmosis - lives in the environment, often in association with large amounts of bird or bat droppings
• Fungal diseases that affect people with weakened immune systems

  • Aspergillosis
  • Candida auris infection
  • Invasive candidiasis
  • Pneumocystis pneumonia (PCP)
  • Candidiasis
  • Cryptococcus neoformans infection
  • Mucormycosis
• Ways fungi reproduce asexually


  • By the growth and spread of hyphal filaments
  • By the asexual reproduction of spores (conidia)
  • By simple cell division, as in budding yeasts
• Types of sexual spores

  • Ascospores - Formed in a sac-like cell known as an ascus containing 8 within (Ascomycetes)
  • Basidiospores - Produced on a specialized club-shaped structure called a basidium (Basidiomycetes)
  • Zygospores - Thick-walled spore (Zygomycetes)
• Sexual reproduction


  The spores develop from the fusion of either unicellular gametes or unicellular hypha (gametangia). Can originate from the fusion of two haploid cells to yield a diploid cell; this then undergoes meiosis and mitosis to yield individual haploid spores. Sexual spores are typically resistant to drying, heating, freezing, and some chemical agents.
• Types of asexual reproduction

  • Fragmentation: fragments of hyphae can grow new colonies and occurs when a mycelium separates into pieces with each component growing into a separate mycelium
  • Budding: somatic cells in yeast form buds (bulge forms on the side of the cell, the nucleus divides mitotically, and the bud ultimately detaches itself from the mother cell)
  • Asexual spores: most common mode of asexual reproduction which are produced by one parent only (through mitosis) and are genetically identical to that parent
• Types of asexual spores

  • Endogenous spores (sporangiophores) - Contained within the sporangium formed at the tip of a supporting hyphae called sporangium. Can be: motile (zoospores) or non-motile
• Cetes (Rhizopus)

  Sexual Reproduction: The spores develop from the fusion of either unicellular gametes or unicellular hypha (gametangia). Can originate from the fusion of two haploid cells to yield a diploid cell; this then undergoes meiosis and mitosis to yield individual haploid spores. Sexual spores are typically resistant to drying, heating, freezing, and some chemical agents
• Fungal Reproduction and Phylogeny Asexual Reproduction

  1. Fragmentation: fragments of hyphae can grow new colonies and occurs when a mycelium separates into pieces with each component growing into a separate mycelium

  2. Budding: somatic cells in yeast form buds (bulge forms on the side of the cell, the nucleus divides mitotically, and the bud ultimately detaches itself from the mother cell)

  3. Asexual spores: most common mode of asexual reproduction which are produced by one parent only (through mitosis) and are genetically identical to that parent
• Types of asexual spores

  • Endogenous spores (sporangiophores): Contained within the sporangium formed at the tip of a supporting hyphae called sporangium. Can be: motile (zoospores) or non-motile (aplanospores)
  • Exogenous spores (conidiophores): Spores that are released directly from the tip or side of the hypha. Can be: thallic or blastic
• Fungi share an ancestor with animals, and are more closely related to animals than any other eukaryotic group. The last common ancestor of all fungi likely existed sometime between 450 million and 1.5 billion years ago
• Chytridiomycota


  An unusual group of motile fungi that produce zoospores
• Microsporidia


  Obligate parasites of a wide variety of animal hosts including humans
• Zygomycota


  Known primarily for their role in food spoilage, and are commonly found in soil and on decaying plant material
• Glomeromycota


  Important fungi in certain mycorrhizal associations
• All of these fungi (Zygomycota and Glomeromycota) are coenocytic (multinucleate), and a unifying feature is the formation of sexual spores called zygospores