Chapter 12: The Eukaryotes – Fungi, Algae, Protozoa, and Helminths

Fungi: General Characteristics

Introduction to Mycology

Mycology is the branch of microbiology that studies fungi, a diverse group of eukaryotic organisms. Fungi play essential roles in ecosystems as decomposers, pathogens, and symbionts.

• Mycology: The scientific study of fungi.

• Chemoheterotrophs: Fungi obtain energy and carbon by consuming organic matter.

• Most fungi are aerobic or facultative anaerobic.

• Fungi decompose organic matter, recycling nutrients in ecosystems.

Comparison of Fungi and Bacteria

Table: Selected Features of Fungi and Bacteria

This table highlights the major differences between fungi and bacteria, focusing on cell type, membrane composition, cell wall structure, reproduction, and metabolism.

Feature	Fungi	Bacteria
Cell Type	Eukaryotic	Prokaryotic
Cell Membrane	Sterols present	Sterols absent (except Mycoplasma)
Cell Wall	Glucans, mannans, chitin (no peptidoglycan)	Peptidoglycan
Reproduction	Sexual and asexual reproductive spores	Endospores (not for reproduction); some asexual reproductive spores
Metabolism	Limited to heterotrophic; aerobic, facultatively anaerobic	Heterotrophic, autotrophic; aerobic, facultatively anaerobic, anaerobic

Major Features of Fungi

Diversity and Structure

Fungi are a highly diverse group, with over 600,000 species identified. They exhibit a range of forms and lifestyles, from unicellular yeasts to multicellular molds.

• Over 600,000 species of fungi exist.

• Most fungi are multicellular; yeasts are unicellular.

• Fungi do not carry out photosynthesis.

• They absorb nutrients from their environment.

• Fungi include pathogens and saprobes (decomposers).

Nutritional Adaptations of Fungi

Environmental Tolerance

Fungi are adapted to survive and thrive in a variety of environmental conditions, often where other organisms cannot.

• Fungi grow best at pH 5 (more acidic than most bacteria).

• They can grow in high sugar and salt concentrations; resistant to osmotic pressure.

• Fungi can grow in low moisture content environments.

• They can metabolize complex carbohydrates that many other organisms cannot.

Vegetative Structures of Fungi

Molds and Fleshy Fungi

The main body of a fungus is called the thallus, which consists of thread-like structures called hyphae. A mass of hyphae forms a mycelium.

• Vegetative hyphae obtain nutrients.

• Aerial hyphae are involved in reproduction.

• Mycelium: A network of hyphae that forms the visible part of the fungus.

Yeasts

Yeasts are unicellular fungi that reproduce by budding or fission. Some fungi are dimorphic, meaning they can exist as both yeast and mold forms depending on environmental conditions.

• Budding yeasts divide unevenly, producing a smaller daughter cell.

• Fission yeasts divide evenly to produce two equal cells.

• Dimorphic fungi are yeastlike at 37°C and moldlike at 25°C.

• Many pathogenic fungi are dimorphic, allowing them to adapt to different host environments.

Example: Candida albicans is a dimorphic fungus that can cause opportunistic infections in humans.