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 sources of industrial products.

• Mycology: The scientific study of fungi.

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

• Most fungi are aerobic or facultative anaerobes.

Comparison of Fungi and Bacteria

Fungi and bacteria differ in cellular structure, metabolism, and reproduction. The following table summarizes key differences:

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

Fungi are a large and diverse group of organisms with unique biological properties.

• There are over 600,000 different species of fungi.

• 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 that may inhibit other organisms.

• Fungi grow best at pH 5, which is more acidic than most bacteria prefer.

• They can grow in high sugar and salt concentrations, making them resistant to osmotic pressure.

• Fungi can grow in low moisture content environments.

• They are capable of metabolizing complex carbohydrates.

Vegetative Structures of Fungi

Molds and Fleshy Fungi

The main body of a fungus is called the thallus, which consists of long filaments known as hyphae. A mass of hyphae forms a mycelium.

• Vegetative hyphae are responsible for nutrient absorption.

• Aerial hyphae are involved in reproduction.

Yeasts

Yeasts are unicellular fungi that reproduce by budding or fission.

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

• Fission yeasts divide evenly to produce two new cells.

Dimorphic Fungi

Dimorphic fungi can exist in two forms depending on environmental conditions, often related to temperature.

• Yeastlike at 37°C (body temperature), moldlike at 25°C (room temperature).

• Dimorphism is common among pathogenic fungi.

• Dimorphic fungi cycle between having hyphae and living as a yeast-like form.

Example:

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

Additional info: Dimorphism allows fungi to adapt to different host environments and is a key factor in their pathogenicity.