mycology

• Mycology is the study of fungi
• Fungi


  Eukaryotic organisms with vegetative forms that do not move due to rigid cell walls containing chitin, cell membranes predominantly contain ergosterol. heterotrophs that obtain energy from external digestion of organic matter, can be saprophytes, parasites or mutualists.They have vegetative forms that are either filamentous tubes (hyphae) or individual cells (yeast), produce a range of spores for sexual or asexual reproduction and dispersal
• Fungal diversity


  • Over 120,000 named species
  • Estimated 2 to 5 million species
  • Majority are microscopic
  • Some have obvious fruiting bodies
  • Some can have giant proportions (e.g. Armillaria ostoyae - honey fungus in Oregon covering 965 hectares, weighing 600 tons and over 2,400 years old)
• Historic fungal taxonomy and nomenclature

  • Ascomycota (sexual spore formation in sacs called asci)
  • Basidiomycota (sexual spore formation on basidia)
  • Zygomycota (sexual spore formation as thick-walled zygospores)
  • Deuteromycota ("Fungi Imperfecti" - no known sexual form)
• Modern taxonomy (molecular phylogeny) uses nuclear ribosomal operon (rDNA) analysis, including 18S, 28S, ITS1 and ITS2 regions, as well as protein-coding genes like translation factor 1-α, β-tubulin, actin, and RNA polymerase II
• There are currently 12 acknowledged fungal phyla, although an alternative classification has 19 phyla
• Many fungal species have both sexual (teleomorph) and asexual (anamorph) forms, which were historically described separately and given different names
• Major fungal phyla


  • Ascomycota (largest phylum with over 83,000 named species, includes yeasts, filamentous fungi, lichens, mycorrhizal species)
  • Basidiomycota (over 48,000 described species, include mushrooms, jelly fungi, yeasts, rusts, smuts)
  • Mucormycota (less than 1% of described species, include food spoilage microorganisms)
• Importance of fungi beyond human infections


  • Primary metabolites
  • Diseases of agricultural crops and wildlife (direct pathogenesis and toxin production)
  • Bioremediation
  • Secondary metabolites
  • Management of pests and diseases
  • Nanoparticle production
• The "One Health" focus highlights the significance of fungi in causing disease in humans, plants and animals, and the concerns regarding antifungal resistance, particularly the impact of antifungal use in agriculture on human pathogens
• Fungal cell structure


  Eukaryotic organisms with DNA organised into chromosomes within a nucleus, distinct cytoplasmic organelles like endoplasmic reticulum, Golgi apparatus, mitochondria, and storage vacuoles, similar biosynthetic pathways to mammalian cells (DNA replication and protein synthesis)
• Fungal species


  • Saccharomyces cerevisiae
  • Beauveria bassiana
  • Penicillium chrysogenum
  • Penicillium citrinum
  • Streptomyces carbophilus
  • Many ascomycete species
• "One Health" Focus on Mycology 2019 report from American Society for Microbiology
• Significance of fungi


  • Causing human disease
  • Causing disease in plants and animals
• Concerns regarding resistance, particularly the impact that antifungal use in agriculture has on human pathogens (one health)
• Fungal cell structure and organisation


  • Eukaryotic organisms
  • DNA organised into chromosomes within nucleus
  • Distinct cytoplasmic organelles (endoplasmic reticulum, Golgi apparatus, mitochondria, storage vacuoles)
  • Similar biosynthetic pathways to mammalian cells
• Fungal cell wall


  • Rigid layer of chitin, layers of polypeptides with complex polysaccharides
  • Mammalian cells lack cell wall
  • Complex network of proteins and polycarbohydrates
  • β-glucan
• Fungi are defined as 'aerobic'
• Fungal metabolism


  • Heterotrophs – specialised at obtaining nutrients from their environment
  • Medically relevant species grow at body temperature - thermotolerance
  • Must obtain nutrients from human host
  • Can colonise all parts of human body
• Obtaining nutrients from human host

  • Glucose – preferred carbon source for most fungi
  • Concentration varies substantially within body
  • Following phagocytosis, Candida albicans metabolism switches from glycolysis to fatty acid β-oxidation, glyoxylate cycle and gluconeogenesis
  • Non-glucose based carbon sources gained by active hydrolysis of host proteins or phospholipids
  • Many pathogens produce proteases, lipases and phospholipases
  • Micronutrients, iron and zinc, present in very low concentrations - rate limiting for growth in vivo
• Micronutrient acquisition

  • Nutritional immunity – "host evolved strategies to restrict microbial access to micronutrients"
  • Pathogenic fungi have evolved efficient micronutrient scavenging systems
  • Iron – essential for host and fungi
  • Aspergillus fumigatus produces iron chelators (siderophores) with high affinity for iron
  • Candida albicans and Cryptococcus neoformans exploit siderophores produced by bacteria
  • Iron can be acquired from haemoglobin
  • Zinc, manganese and copper = trace metals essential for growth and survival of fungi
  • Fungal vacuole important for cellular zinc homeostasis
  • Numerous metal iron transporters have been identified
• Fungal morphology


  • Candida albicans - yeast cells, pseudohyphae or hyphae
  • Pleiotropic nature not linked to temperature or virulence
  • Dimorphic fungal pathogens
  • Primary fungal pathogens - >1 million new infections per year in US
  • Dimorphism – temperature regulated
  • Ambient - filamentous moulds
  • Infectious propagule – spore produced by filamentous form
  • 37°C - yeast
• Fungal growth forms


  • Yeasts - unicellular growth, often can be cultured and identified with similar methods to bacteria
  • Moulds - hyphal growth, forming mycelium, culture often takes longer identification through analysing spore formation
  • Dimorphic - 37°C yeast and mould forms, ≤30°C mould form
• Growth of filamentous fungi


  • Growth is in the form of microscopic branching filaments – hyphae
  • Can be septate, pigmented or coenocytic (non-septate) or hyaline (colourless)
• Asexual reproduction - conidia


  • By differentiation of the mycelium into non-motile spores - conidia
  • Macroconidia (large/complex)
  • Microconidia (small/simple)
• Asexual reproduction – thallic conidia


  • Develop within the preformed hypha
  • Arthrospores – the hypha is divided by septa then fragments
  • Chlamydospores – formed by thickening of the cell wall in a compartment of the hypha
• Asexual reproduction – blastic conidia


  • Develop from the tip of the hypha (usually on specialised structures)
  • Blastoconidia - by budding
  • Poroconidia - through a pore
  • Phialoconidia - by extrusion
• Asexual reproduction – sporangiospores and zoospores


  • Many Mucormycota species produce Sporagngiospores within a sporangium
  • Chytridomycota produce zoospores within zoosporangia. Zoospores are motile by means of a flagellum
  • Spores formed within an enclosure
• Saprophytes


  Microorganism that lives on dead or decaying organic matter
• Mutalists


  Organisms in a mutualistically beneficial relationship
• What differentiates fungi 


  They produce a huge range of spores
• Why is fungi having a similar biosynthetic pathway as mammalian cells a problem?

  It makes designing an antifugal drug very difficult, as you have to be very precise.