Lectures 5 & 6. Fungi 3 & 4. Vladimir

Overview of Fungi

• Fungi are an integral and diverse kingdom of organisms with several distinguishing characteristics.

  • Cell Walls: Composed of chitin, differing from plant cell walls which contain cellulose.

  • Cellular Structure: Mostly multicellular, except for yeasts which are unicellular or can form pseudo-hyphae.

Nutritional Mode

• Heterotrophic Nature: Fungi acquire nutrients by breaking down organic matter from their surroundings.

  • They generally live in environments rich in carbon compounds, primarily organic matter like sugars.

  • Extracellular Enzymes: Fungi secrete enzymes that decompose complex compounds, releasing essential nutrients.

Major Groups of Fungi

• Fungi reproduce both sexually and asexually, with structures such as:

  • Hyphae: Multicellular filaments that can be septate (with divisions) or coenocytic (without divisions).

  • Different reproductive strategies exist; yeast can reproduce through budding or fission.

Ecological Roles

• Decomposers: Vital for nutrient cycling in ecosystems, breaking down dead organic material.

• Symbiotic Relationships:

  • Mycorrhizae: Fungi form associations with plant roots, enhancing nutrient uptake.

    • Ectomycorrhizae: Form a sheath around roots; they do not penetrate cells.

    • Endomycorrhizae: Penetrate root cells to directly access nutrients.

• Pathogens/Parasites: Opportunistic and obligate pathogens can exploit hosts, leading to diseases.

Harmful Fungi

Poisonous Mushrooms

• Toxicity: Many mushrooms possess toxins as a defense mechanism.

  • Amanita muscaria: Known for hallucinogenic properties; not highly poisonous but can cause discomfort.

  • Deadly Varieties: Death Cap (Amanita phalloides) and Destroying Angel (Amanita virosa) can cause severe liver damage.

  • Poisoning incidents occur globally, often through misidentification.

• Toxin Mechanism: Cyclic peptides that affect cellular processes like RNA polymerase, leading to cell death.

  • Symptoms can worsen after an initial period of improvement.

Toxic Molds

• Ergot (Claviceps purpurea): A mold associated with rye that can cause severe health issues.

  • In infected grains, it forms dark structures called sclerotia, which impact the plant's vascular system, leading to toxic effects in humans.

  • St. Anthony's Fire: Historical name for ergotism due to burning pain in extremities from vasoconstriction.

• Aflatoxins: Produced by Aspergillus species; found on crops like peanuts.

  • Aflatoxins are carcinogenic and can result in severe liver damage.

Plant Pathogens

• Rusts and Smuts:

  • Affect various crops and plants, often leading to significant agricultural loss.

  • Rusts: Require two different host species to complete their lifecycle; for example, Puccinia graminis infects cereal crops and barberry.

  • Smut: Typically infects one host, like Ustilago, which affects grains.

Tree Pathogens

• Dutch Elm Disease: Caused by the fungus Ophiostoma, spread by beetles.

  • The fungus proliferates in the xylem, blocking nutrient transport and eventually causing tree death.

• Honey Fungus: A network of mycelium that can infect trees over vast areas.

  • Notably, a colony in Oregon spans 3.4 square miles.

Wood Decay Fungi

• Brown, White, and Soft Rot: Fungi that degrade timber.

  • Affect cellulose in timber, breaking it down into sugars for nourishment.

  • Manage with dry environments, fungicides, and potential biological control agents like Trichoderma.

Fungal Diseases in Humans

• Examples of diseases caused by fungi include:

  • Candidiasis: Caused by Candida species, particularly Candida albicans, affects immunocompromised individuals.

  • Aspergillosis: Inhalation of Aspergillus spores causing lung infections and other systemic issues.

  • Cryptococcosis: Infection from inhaling spores found in bird droppings; can lead to meningitis.

  • Allergic Reactions: Triggered by inhalation of fungal spores, resulting in asthma and other sensitivities.

• Opportunistic Mycoses: Fungi exploit compromised immune systems, leading to infections from common yeasts.

Microsporidia

• Unique group of fungi; known for their specialized life cycles and lack of mitochondria.

  • Historically discovered in immunocompromised individuals, particularly AIDS patients.

  • Infect through a polar tube, injecting their spores into host cells, and reproduce within. needle

Summary Points

• Fungi play a crucial role in ecosystems but can also cause significant harm to humans, plants, and animals.

• Awareness of the beneficial and harmful aspects of fungi is critical for public health and agriculture.