21Introduction_to_fungi_mini_21

Introduction to Fungi

Mycology

• The study of fungi.

Fungal Cells

• Fungi are eukaryotic organisms.

• Cell Structure:

  • DNA is contained within a bound nucleus.

  • Cell Walls:

    • Composed of chitin and glucans, making them thick.

  • Pigments:

    • Some may produce pigments that can be toxic and protect against UV radiation.

  • Plasma Membrane:

    • Similar to animal cells but cholesterol is replaced with ergosterol.

Fungal Growth

• Types:

  • Unicellular (e.g., yeasts like Candida sp.)

  • Multicellular (e.g., composed of hyphae)

• Growth Cycle:

  • Includes vegetative and reproductive stages.

  • Vegetative Stage:

    • Mycelium, which is a tangle of hyphae, allows growth through various media.

    • Can form large masses, up to 2,000 acres in size.

  • Reproductive Stage:

    • Produces mushrooms.

• Hyphae Structure:

  • Divided into singular cells connected by septa.

Fungal Nutrition

• Types of Nutritional Strategies:

  • Obligate Aerobes: Require oxygen for growth.

  • Obligate Anaerobes: Cannot tolerate oxygen (toxic to them).

  • Facultative Anaerobes: Prefer oxygen but can survive in its absence.

• Fungi are heterotrophs, utilizing several strategies:

  • Saprobes: Obtain energy from dead or decaying matter.

  • Parasitic Fungi: Extract nutrients from a host organism, can be detrimental.

  • Predatory Fungi: Such as nematophagous fungi that prey on nematodes.

• Digestion:

  • External digestion by secreting enzymes to break down complex molecules before absorbing nutrients.

  • Ability to digest cellulose and lignin, making them significant in ecological recycling.

  • Haustoria: Specialized hyphae that inject enzymes for nutrient absorption.

Fungal Reproduction

• Can reproduce both sexually and asexually.

• Fungal Types:

  • Perfect Fungi: Capable of both sexual and asexual reproduction.

  • Imperfect Fungi: Asexually reproduce through mitosis.

• Asexual Reproduction Methods:

  • Fragmentation, budding, and formation of spores (via mitosis).

  • Sporangium: The reproductive sac where spores are produced.

  • Conidiospores: Released from hyphae, can be unicellular or multicellular.

• Sexual Reproduction:

  • Often initiated by adverse environmental conditions.

  • Forms two mating types:

    • Homothallic: Can self-fertilize (same mycelium).

    • Heterothallic: Requires two different, compatible mycelia.

• Three Stages of Sexual Reproduction:

  • Plasmogamy: Fusion of cytoplasm leads to dikaryotic cells with two haploid nuclei.

  • Karyogamy: Fusion of nuclei creates a diploid zygote nucleus.

  • Meiosis: Results in the release of spores into the environment.