AS

Fungi Pres.students

Fungi Overview

  • Fungi are diverse and widespread organisms.

  • They play a crucial role in terrestrial ecosystems by breaking down organic material and recycling vital nutrients.

  • Approximately 100,000 species of fungi are described, but estimates suggest there may be 1.5 million total species.

Nutrition and Ecology

  • Fungi are heterotrophs, absorbing nutrients from the environment.

  • They utilize enzymes to decompose complex molecules into smaller organic compounds, showcasing their ecological adaptability and success.

Diverse Lifestyles of Fungi

  • Fungi can exhibit various lifestyles:

    • Decomposers: Break down organic matter.

    • Parasites: Live off a host organism.

    • Mutualists: Engage in beneficial relationships with other organisms.

Body Structure of Fungi

  • Common structures include multicellular filaments and single cells (yeasts).

  • Some species can exist in both forms, while others are strictly filamentous or yeast.

  • The morphology of multicellular fungi enhances nutrient absorption:

    • They consist of mycelia, a network of branched hyphae optimized for absorption.

    • Mycelium maximizes surface-to-volume ratio, allowing efficient nutrient intake.

    • Fungal cell walls contain chitin.

Fungal Phyla

Basic Features

  • Chytridiomycota: Have flagellated spores.

  • Zygomycota: Recognized for their zygosporangium as a sexual stage.

  • Glomeromycota: Form arbuscular mycorrhizae with plants.

  • Ascomycota: Produce sexual spores in sacs called asci and vast numbers of conidia.

  • Basidiomycota: Characterized by elaborate fruiting bodies known as basidiocarps.

Hyphal Structures

  • Most fungi possess hyphae divided by septa, featuring pores for organelle movement.

  • Coenocytic fungi lack septa, presenting a continuous cytoplasmic mass containing numerous nuclei.

Mycorrhizal Fungi

  • Mycorrhizal fungi utilize specialized hyphae known as haustoria, penetrative structures that enable nutrient transfer from host plants.

  • They deliver essential phosphate ions and minerals to plants, vital for most vascular plants.

  • Mycorrhizal fungi colonize soils by the dispersal of haploid cells called spores.

Fungal Reproduction

Sexual Reproduction

  • Fungi can reproduce through sexual or asexual cycles.

  • Fungal nuclei are generally haploid, with transient diploid stages during sexual reproduction.

  • Plasmogamy: Fusion of parent mycelia, leading to a heterokaryon state, where haploid nuclei exist together before fusing.

  • In some species, haploid nuclei can pair in a dikaryotic mycelium.

  • Fungi use sexual signaling molecules called pheromones to attract compatible mating partners, facilitating the process of sexual reproduction and genetic diversity.

Asexual Reproduction

  • Many fungi reproduce asexually, producing haploid spores via mitosis.

  • Yeasts reproduce asexually by budding, creating “bud cells” from a parent.

Evolutionary Relationships

  • The ancestor of fungi was an aquatic single-celled flagellated protist.

  • Fungi share a closer evolutionary relationship with animals than with plants or other eukaryotes.

Chytrids and Zygomycetes

Chytrids (Chytridiomycota)

  • Adapted to freshwater, marine, and terrestrial ecosystems.

  • Unique for flagellated spores called zoospores.

  • Chytrids can be decomposers, parasites, or mutualists.

  • Example: Batrachochytrium dendrobatidis, linked to amphibian decline.

Zygomycetes (Zygomycota)

  • Diverse in life histories, often fast-growing molds.

  • Characterized by coenocytic hyphae and typical life cycles illustrated by Rhizopus stolonifer.

Ascomycetes (Ascomycota)

  • Found in a variety of habitats; produce sexual spores in asci within fruiting bodies (ascocarps).

  • Include plant pathogens, decomposers, and symbionts; reproduce asexually through conidia.

Basidiomycetes (Basidiomycota)

  • Include mushrooms and shelf fungi, distinguished by the clublike basidium, which produces sexual spores (basidiospores).

  • The life cycle includes a long-lived dikaryotic mycelium.

Ecological Roles

  • Fungi serve critical roles in nutrient cycling, mutualistic interactions, and impacting human welfare.

Mutualistic Relationships

  • Mycorrhizae play a significant role in ecosystem and agricultural health.

  • Endophytes provide benefits by deterring herbivores and protecting against pathogens.

Lichens

  • Represent a symbiotic association between a fungus and photosynthetic organisms (algae/cyanobacteria).

  • Important ecological pioneers on new substrates (rock, soil).

Fungal Pathogens

  • About 30% of recognized fungal species are parasitic, affecting primarily plants.

  • Notable disease-causing fungi include those that impact food crops, potentially harming human health.

Ergot and its Impacts

  • Ergotism, caused by the ascomycete Claviceps purpurea, led to historical epidemics and contains compounds used to synthesize LSD.

Practical Uses of Fungi

  • Fungi are utilized in human diets, for making cheese and beers, and producing antibiotics like Penicillium.

Fungi: A group of diverse and widespread organisms that play a crucial role in ecosystems by breaking down organic material and recycling nutrients.

Decomposers: Organisms that break down dead organic matter, returning nutrients to the soil and ecosystems.

Parasites: Organisms that live off a host organism, often harming it in the process.

Mutualists: Organisms that engage in beneficial relationships with other organisms, providing advantages to each other.

Hyphae: Filamentous structures that make up the body of fungi, optimized for nutrient absorption.

Mycelium: A network of branched hyphae that enhances nutrient absorption by increasing surface area.

Chitin: A structural polysaccharide found in fungal cell walls, providing strength and rigidity.

Spores: Reproductive units of fungi that can develop into new individuals upon germination.

Dikaryotic: A stage in some fungi where two genetically distinct nuclei coexist in the same cell before fusion.

Mycorrhizae: Symbiotic associations between fungi and plant roots that enhance nutrient and mineral uptake for plants.

Endophytes: Fungi or bacteria that live inside a plant without causing harm, often providing benefits like pathogen protection.

Lichens: A symbiotic association between a fungus and photosynthetic organisms such as algae or cyanobacteria. Mutualistic relationship.