Fungi: Characteristics and Hyphae

• Chapter 31 is about Fungi.

Characteristics of Fungi

• Fungi are multicellular eukaryotes with the exception of yeasts
• Fungi obtain nutrition as heterotrophs through absorption
• Fungi secrete enzymes to break down food molecules outside their cells, then absorb the nutrients across their cell walls
• Saprophytes live on dead organic matter
• Parasites benefit at the expense of a host
• Mutualistic relationships benefit both the host and the fungi
• Hyphae are filaments which constitute the structure of fungi, these cell walls are made of chitin
• Mycelium is the network of hyphae
• Septate hyphae are divided into cells by septa (walls)
• Aseptate hyphae are multinucleate, long tubes described as coenocytic with continuous cytoplasmic mass

Specialized Hyphae

• Haustoria are nutrient-absorbing hyphae found in both parasitic and mutualistic fungi, and penetrate the cell walls of hosts to extract nutrients
• Some fungi have modified hyphae, such as hoops, to penetrate and digest living animals
• Mycorrhizae are a specialized type of hyphae.
• Ectomycorrhizal fungi form sheaths of hyphae over the root and in extracellular spaces
• Arbuscular (endomycorrhizal) fungi branch hyphae through the root cell walls, forming tubes through which they penetrate the root plasma membrane

Growth and Reproduction

• Most fungal hyphae are haploid
• Fungi exhibit both sexual and asexual reproduction, releasing spores that are haploid and unicellular
• Fungal reproduction does not include a flagellated stage
• Fusion of cytoplasm and nuclei occur at different times during sexual reproduction
• Plasmogamy is the fusion of cytoplasm from two mycelia
• In plasmogamy, the nuclei do not fuse, resulting in a heterokaryon (different nuclei)
• Karyogamy is the fusion of nuclei that creates a zygote
• Meiosis follows karyogamy, producing spores that grow into hyphae, which are (n)

Reproduction

• Many fungi can reproduce asexually
• Mold sometimes grows on fruit, bread and other foods and grows haploid spores
• Other asexual fungi are yeasts
• Yeasts inhabit moist environments
• Yeasts reproduce via simple cell division or budding off

Fungal Phylogeny

• Chytridiomycota (chytrids) have motile spores with flagella and 1,000 species
• Zygomycota have resistant zygosporangium as a sexual stage and 1,000 species
• Glomeromycota form arbuscular mycorrhizae and have 160 species
• Ascomycota (sac fungi) bear sexual spores internally in sacs called asci and contains 65,000 species
• Basidiomycota (club fungi) have elaborate fruiting bodies called basidiocarps and contains 30,000 species

Phylum Chytridiomycota (Chytrids)

• Chytrids have flagellated spores
• Chytrids play a role in amphibian population decline
• Chytrids attack the keratin layer and 'suffocates' frogs

Phylum Zygomycota

• Zygomycota are zygote fungi-they are molds that cause food to rot
• Zygomycota have coenocytic hyphae with asexual spores
• Zygomycota form a zygospore
• An example of Zygomycota is Rhizopus sp.(bread mold)
• Some zygomycetes, like Pilobolus, "aim" their sporangia toward bright light

Phylum Glomeromycota

• Glomeromycota were once considered zygomycetes, but are now a separate clade
• Glomeromycota are mycorrhizae, associating with plant root hairs
• Ninety-percent of plants have mutualistic partnerships with glomeromycetes
• Glomeromycota increase plant productivity by delivering phosphate and nutrients to plant roots
• Glomeromycota allow plants to supply carbohydrates.

Phylum Ascomycota

• Ascomycota are sac fungi
• Ascomycota contain ascus
• Ascus produces sexual spores in a sac
• Fruiting bodies of fungi are ascocarp's
• Example of phylum ascomycota is orange peel fungus
• Phylum Ascomycota includes single-celled yeasts
• Phylum Ascomycota includes lichen associations
• Phylum Ascomycota includes truffles and morels

Phylum Basidiomycota

• Basidiomycota are club fungi
• Members of Basidiomycota include mushrooms, shelf fungi, and puffballs
• Members of Basidiomycota have clublike structures called basidium
• Clublike structures of members of Basidiomycota result in a transient diploid stage in the life cycle
• In members of Basidiomycota, basidium means 'pedestal'
• Members of Basidiomycota have basidocarps-fruiting bodies that are mushrooms
• Basidiomycota's includes wood decomposers
• Basidiomycota's includes common mushrooms
• Basidiomycota's undergo “fairy rings” i.e. life cycle includes a long-lived dikaryotic mycelium, and its fruiting structure, a mushroom, that can built in just a few hours.

Roles of Fungi

• Fungi aid in digestion of plant material of grazing mammals
• Fungi are 'farmed' by ants and termites
• Penicillium is a mold that is in the antibiotic family
• Truffles, morels, chanterelles, blue cheese, alcohol, and bread are food products that are products of fungi
• Fungi can cause disease
• Fungi can cause blight in plants
• Fungi can cause ringworm in humans
• Cryptococus gattii is a deadly basidiomyctes fungus found on Vancouver Island
• Cryptococus gattii causes disease

Claviceps Purpurea (Ergot)

• A type of ascomycetes
• Cool, wet years result in higher rates of ergot infection
• Ingestion of Ergot lowers immunity
• Black plague hit harder in areas where rye bread that was ingested was contaminated with ergot
• Ergot ingestion leads to miscarriages and lower fertility
• Ergot ingestion leads to hallucination and twitching
• All of the above negative effects of ergot were blamed on witches
• Ergot is used to treat migraines, stimulate labour, and is a source of LSD

Lichens

• A symbiotic relationship of millions of photosynthetic microorganisms, cyanobacteria or green algae.
• The Fungal component of Lichen is most often an ascomycete
• Algae or cyanobacteria occupy an inner layer below the lichen surface