Fungi and Lichen (MB)

Fungal Dimorphism, Disease Classes, and Microsporidia

• Dimorphism in fungi allows them to evade host defenses by residing within phagocytotic cells, shielding them from the immune system
• Failure to switch dimorphically almost always reduces pathogenicity in fungi
• Fungal diseases are caused by inappropriate immune response, toxin production, and host infection (mycosis) with systemic infections being the most serious
• Ascomycota is the largest and most diverse group of fungi, containing single-celled species, filamentous species, and yeasts like Candida albicans
• Saccharomyces cerevisiae is a unicellular fungus, around 6 µm in diameter, studied for basic research and used in biotechnical applications
• Microsporidia are ancient groups of parasitic or saprophytic fungi, closely related to fungi, and infect every vertebrate and invertebrate
• Microsporidia have the smallest genome size of eukaryotes, infect a wide range of hosts, and have three common species that infect humans
• Symptoms of Microsporidia infection include chronic, non-bloody diarrhea and respiratory infections, particularly affecting immunocompromised individuals
• Microsporidia spores are small, non-motile, and highly environmentally resistant, penetrating host cells to begin replication
• Fungi are eukaryotes closer to animals than plants, primarily aerobic, and act as recyclers in the ecosystem
• Pathogenic fungi can switch between multicellular hyphae and single-celled yeasts, with hyphae being septate or coenocytic and forming conidia for spread
• Tasks for further study include reading specific sections of Brock Biology of Microorganisms, exploring Candida albicans as a nosocomial pathogen, and understanding its growth, size, cell shape, and treatment options

Lichen Vegetative Structure and Symbiotic Relationships

• Lichens have a stratified thallus consisting of layers such as the photobiont layer, medulla layer, and lower cortex layer.
• Foliose and fruticose lichens have a lower cortex layer, while crustose and squamulose lichens are directly attached to the substrate at the medulla layer.
• Foliose and fruticose lichens attach to surfaces via rhizines, which secrete extracellular gelatinous materials for attachment.
• Crustose lichens are flatter and closely attached to surfaces, while squamulose lichens have leaf-like areolated thallus structures.
• Fruticose lichens have a shrub or hair-like structure and can resemble plants, with finer, beard-like structures and high surface area for gas diffusion and photosynthesis.
• Lichenized fungi, the mycobiont, are heterotrophic, requiring organic carbon as a carbon source and acquiring carbon from living algae or cyanobacterial cells.
• Lichenized fungi form housing structures that provide adequate lighting and gas exchange for the photobiont, with only about 25% of lichens forming 3D structures such as foliose or fruticose.
• Photobionts are photoautotrophic, requiring light, water, and carbon dioxide for photosynthesis, and release organic carbon, CO2, and minerals leached from the substrate.
• Lichens act as carbon sinks, with 50% of CO2 assimilated during photosynthesis used for respiration and the remaining utilized for thallus cell walls and other compounds.
• Lichens form tripartite symbioses with green algae and cyanobacterial photobionts, with the cyanobacterial partner responsible for nitrogen fixation.
• Lichens serve as bioindicators of air pollution, with fieldwork involving the comparison of lichen biodiversity between car parks and green areas to identify patterns.
• Fieldwork on campus involves photographing all lichens in designated areas, returning to the lecture room for identification, and determining observable patterns in lichen biodiversity.