Fungi and Lichens - Notes for Exam Preparation

Characteristics of Fungi

  • Eukaryotic, non-vascular, non-motile, heterotrophic organisms.
  • Can be unicellular (like yeasts) or filamentous (multicellular).
  • Reproduce by means of spores.
  • Lack chlorophyll; cannot perform photosynthesis.

Saccharomyces cerevisiae

Overview
  • Known as baker's yeast or brewer's yeast.
  • Scientific name 'cerevisiae' comes from the Latin for 'beer'.
  • Plays a crucial role in fermentation of beer and the rising of bread.
Characteristics
  • Mesophilic: optimal growth at about 30°C (86°F), prefers pH 4.0 to 6.0.
  • Cream to light tan color on agar plates.
  • Unicellular, oval-shaped cells, reproduce by budding (a mother cell forms a bud that grows until same size).
  • Naturally found on ripe fruits and tree bark.
Medical Importance
  • Principal model organism in eukaryotic research; fully sequenced genome available.
  • Insights into DNA replication, cell cycles, protein turnover, and stress responses.
  • Used in treating GI disorders like inflammatory bowel disease.
Diseases
  • Invasive Infections (Fungemia): Occurs in immunocompromised individuals, entry into bloodstream.
  • Gastrointestinal Infections: Rare, especially in those with digestive disorders.
  • Can cause endocarditis, vaginitis, skin infections, and more.

Economic Effects of S. cerevisiae

Beneficial
  • Essential in food/beverage fermentation; significant commercial role.
  • Used globally in biotechnology; produces ethanol, biofuels, etc.
Detrimental
  • Potential toxicity risk in engineered uses; cell viability issues.
  • Competition with natural yeasts can disrupt ecosystems.

Penicillium spp.

Overview
  • Genus in phylum Ascomycota, identified by ascospores production.
Characteristics
  • Mesophilic fungi, grow at 5-37°C, optimal 20-30°C, pH 3-4.5.
  • Multicellular, color changes from white to various shades over time.
Medical Importance
  • Source of penicillin – a crucial antibiotic.
  • Used in bioremediation to break down toxins.
Diseases
  • Can cause superficial infections (e.g., keratitis).
  • Associated with chronic pulmonary allergic diseases.
Economic Effects
  • Beneficial in cheese production and organic acid/enzyme production.
  • Detrimental as spoilage agents leading to economic loss in food.

Lichens

  • Formed by symbiotic relationships between fungus and algae/bacteria.
  • Protects and provides a structure; algae/bacteria generate food via photosynthesis.
Characteristics
  • Growth varies: crustose (flat), foliose (leaf-like), fruticose (shrub-like).
  • Very slow growth; sensitive to air pollution.
Medical Importance
  • Source of penicillin and potential in antimicrobial treatments.
Diseases
  • Can cause allergic reactions in some individuals.

Microorganism: Usnea longissima

Overview
  • Known as Methuselah’s beard; hangs from tree branches.
Characteristics
  • Sensitive to environmental changes; bioindicator of air quality.
Medical Importance
  • Contains usnic acid for wound healing; potential gastrointestinal distress in doses.

Flavoparmelia caperata (Greenshield Lichen)

Overview
  • Foliose lichen sensitive to pollution; thrives on tree bark and rocks.
Characteristics
  • Yellow-green color, produces metabolites with antibacterial properties.
Economic Importance
  • Utilized in the perfume/dye industry; traditional medicinal applications.
Detrimental Effects
  • Overgrowth can damage structures and reduce fruit yield in orchards.

Roles in Nature

  • Fungi and lichens are critical decomposers, nutrient cyclers, and air quality indicators.
  • Their interactions with plants include enhancing growth and resilience against diseases.