sPRING2020_Bi202_Fungi 3

Introduction to Fungi

• Fungi are diverse and widespread organisms that play essential roles in terrestrial ecosystems.

• They break down organic materials and recycle vital nutrients.

• Approximately 100,000 species of fungi have been described, with estimates suggesting there may be up to 1.5 million species.

Fungi: Nutrition and Ecology

Nutritional Strategies

• Fungi are absorbtive heterotrophs, meaning they obtain nutrients by absorbing organic compounds from their environment.

• They can act as:

  • Decomposers: Breaking down dead organic material.

  • Parasites: Feeding on living organisms, often harming the host.

  • Mutualists: Engaging in beneficial relationships with other organisms.

• Hydrolytic enzymes produced by fungi break down complex molecules into simpler, absorbable forms.

Fungal Morphology

Body Structures

• Two primary structures:

  • Multicellular Filaments: Composed of mycelium, which consists of networks of branched hyphae adapted for absorption.

  • Single Cells (Yeasts): Yeasts are unicellular fungi.

• Fungal cell walls are made of chitin, distinct from plant cell walls.

Hyphal Structures

• Septate Hypha: Hyphae with septa (cross-walls) that divide them into cells.

• Coenocytic Hyphae: Hyphae without septa, forming a continuous cytoplasmic mass with multiple nuclei.

Fungi Relationships with Plants

Mycorrhizae

• Mycorrhizae: Mutualistic associations between fungi and plant roots.

  • Fungi enhance mineral and phosphate absorption for plants.

  • Plants provide carbohydrates produced via photosynthesis.

• Nearly all vascular plants are associated with mycorrhizae.

Types of Mycorrhizal Fungi

• Ectomycorrhizal Fungi: Form sheaths around roots and grow into root cortex spaces.

• Arbuscular Mycorrhizal Fungi: Extend hyphae through root cell walls to form tubular structures.

Fungal Reproduction

Spores and Life Cycle

• Fungi produce vast numbers of spores for reproduction, which can be:

  • Asexual Spores: Produced via mitosis (e.g., conidia in ascomycetes).

  • Sexual Spores: Formed through complex processes like plasmogamy (fusion of cytoplasm) and karyogamy (fusion of nuclei).

Asexual vs Sexual Reproduction

• Asexual Reproduction: Involves mitosis and may include budding in yeasts.

• Sexual Reproduction involves the fusion of hyphae from different mating types.

• Sexual reproduction results in the formation of a heterokaryotic mycelium, containing different nuclei.

Major Groups of Fungi

Chytrids

• Phylum Chytridiomycota: Unique for having flagellated spores (zoospores); live in freshwater and terrestrial habitats.

Zygomycetes

• Phylum Zygomycota: Known for fast-growing molds like Rhizopus stolonifer (bread mold) and sexually produced zygosporangia.

Glomeromycetes

• Phylum Glomeromycota: Form arbuscular mycorrhizae and were once considered zygomycetes.

Ascomycetes

• Phylum Ascomycota: Known as sac fungi; produce sexual spores in asci and asexual spores as conidia. Includes yeasts and fungi like molds.

Basidiomycetes

• Phylum Basidiomycota: Known as club fungi; produce basidia and basidiospores. Includes mushrooms and shelf fungi.

Fungi as Decomposers

• Fungi are crucial in breaking down organic material, recycling nutrients in ecosystems, and serving as important composters in nature.

Fungi as Parasites

• Approximately 30% of known fungi are parasitic, primarily affecting plants.

  • Example: Ergot of Rye, known for its toxicity, caused historical outbreaks of ergotism.

Mycosis in Humans

• Mycosis: General term for fungal infections in animals; examples include ringworm and athlete's foot. Some fungi can be opportunistic pathogens.

Practical Uses of Fungi

• Humans consume many fungi; they are also crucial in producing foods, beverages, and antibiotics (e.g., Penicillium).

• Genetic research on fungi leads to advances in biotechnology, including insulin production and biofuel development.

Summary of Fungal Characteristics

• Distinctions among phyla:

  • Chytridiomycota: Flagellated spores

  • Zygomycota: Resistant zygosporangium

  • Glomeromycota: Arbuscular mycorrhizae

  • Ascomycota: Spores in sacs

  • Basidiomycota: Club-like fruiting bodies.

Key Concepts

• Recognize the importance of fungi in ecosystems, their roles in mutualism and decomposition, their life cycles, and their applications in various fields.