2.4 Fungi-1.pdf

2.4 Fungi Domain Eukarya, Kingdom Fungi Figure 24.1 Many species of fungus produce the familiar mushroom (a) which is a reproductive structure. This (b) coral fungus displays brightly colored fruiting bodies. This electron micrograph shows (c) the sporebearing structures of Aspergillus, a type of to...

2.4 Fungi Domain Eukarya, Kingdom Fungi Figure 24.1 Many species of fungus produce the familiar mushroom (a) which is a reproductive structure. This (b) coral fungus displays brightly colored fruiting bodies. This electron micrograph shows (c) the sporebearing structures of Aspergillus, a type of toxic fungus found mostly in soil and plants. (credit “mushroom”: modification of work by Chris Wee; credit “coral fungus”: modification of work by Cory Zanker; credit “Aspergillus”: modification of work by Janice Haney Carr, Robert Simmons, CDC; scale-bar data from Matt Russell) Evolution of Fungi Monophyletic group Plants, animals, and fungi trace their ancestry to protists ○ Flagellated unicellular protist was most likely the common ancestor Molecular data shows that animals and fungi shared a common ancestor after plants evolved. ○ Animals and fungi are more closely related to each other than either is to plants. Characteristics of Fungi Mostly multicellular spp that prefer moist, slightly acidic environments Unicellular = yeasts Most are haploid for the majority of their life cycle Contain chitin in their cell walls Most produce spores None are photosynthetic, all are heterotrophic Vary in oxygen requirements Obligate aerobes: require oxygen Obligate anaerobes: only use anaerobic respiration Facultative anaerobes: aerobic or anaerobic respiration Fungi and Other Groups Shared characteristics with plants ○ ○ Shared characteristics with bacteria ○ ○ Cell wall (but not made of cellulose) Immobile Decomposers Absorb nutrients across the cell surface Shared characteristics with animals ○ ○ ○ ○ Heterotrophic Chitin in cell walls similar to exoskeleton of arthropods Melanin pigment Store carbohydrates as glycogen Cell Structure and Function Eukaryotic cellular organization Membrane-bound nucleus Linear DNA wrapped around histones Complex system of internal membranes Endoplasmic reticulum Golgi apparatus Mitochondria Morphology of Multicellular Fungi Hyphae: long, branching filamentous structures; excrete digestive enzymes into the environment and then absorb nutrients Mycelium: mass of hyphae; vegetative stage Fruiting body: reproductive structure for dispersal of spores Fungal Morphology Hyphae can be: Septated: divided into separate cells with perforations between to allow flow of nutrients Coenocytic or aseptate: not separated; large cells with many nuclei Metabolism and Nutrition Mostly obligate aerobes, some obligate anaerobes Heterotrophic: obtain C and N from food External digestion: digestion occurs before ingestion ○ ○ Decomposers: break down insoluble polysaccharides → glucose ○ Saprophytic: nutrients from decaying organic matter Mutualists: mycorrhizal fungi form relationships with plants ○ ○ ○ Enzymes secreted from hyphae to process nutrients in the environment Smaller molecules are absorbed through the large surface area of the mycelium Fungi gain sugars Plants gain water and nutrients 80-90% of plants rely on mycorrhizal fungi Parasites: infect animals or plants Reproduction of Fungi Sexual and/ or asexual reproduction produces spores from the sporangium Release of spores from a sporangium at the end of a hypha called a sporangiophore. Figure 24.8 Generalized fungal life cycle. Fungi may have both asexual and sexual stages of reproduction. Life Cycle Haplontic life cycle: haploid stage is dominant life stage Multicellular stage = haploid Zygote = diploid Asexual Reproduction of Fungi Asexual spore production: haploid spores are cloned via mitosis = genetically identical to parent Fragmentation: breaking off Budding ○ ○ ○ Bulge forms on the side of the cell Nucleus divides mitotically Bulge “buds” off from mother cell Figure 24.7 Budding in Histoplasma. Sexual Reproduction of Fungi Often occurs in response to environmental stresses → introduce genetic variation Mating types are produced in the mycelium ○ ○ Homothallic: both types present → self fertile Heterothallic: one type present → requires two different organisms Three stages ○ ○ ○ Plasmogamy: haploid hyphae cells fuse Dikaryotic stage: two haploid nuclei in one cell Karyogamy: haploid nuclei fuse → diploid zygote Meiosis results in haploid spores that germinate into haploid hyphae without embryological development Classification of Fungi Five phyla based on mode of reproduction and/ or molecular data Figure 24.10 Fungal phyla. Chytridiomycota – Chytrids Simplest and most primitive fungi Primarily unicellular and aquatic Only fungi spores with flagella Parasites & saprobes ○ Causes infection in amphibians and has caused some extinctions Asexual and/ or sexual reproduction Glomeromycota Small group of species Arbuscular mycorrhizae: mutualistic relationship between hyphae and tree roots = cannot survive without plant roots Only asexual reproduction Zygomycota Conjugated or zygote-producing fungi Asexual reproduction is more common; produces sporangiospores Sexual reproduction: conjugation requires two opposing mating strains (+ and -) and forms zygosporangium with zygospores Mainly saprobes Bread mold: Rhizopus Left: Rhizopus sporangia with asexual spores Right: Sexual conjugation in Rhizopus resulting in zygosporangium Rhizopus spores. Asexual sporangia grow at the end of stalks, which appear as (a) white fuzz seen on this bread mold, Rhizopus stolonifer. The black tips (b) of bread mold are the spore-containing sporangia. Ascomycota: Sac Fungi Most common type of fungus ○ ○ Morels, truffles, baking/ brewing/ fermenting yeasts, Penicillium, Dutch elm disease Aspergillus and Candida cause human infections Hyphae congregate to form fruiting body Reproductive structures ○ ○ Ascus: sac-shaped structure that contains ascospores (sexual spores) Conidiophore: contain conidia (asexual spores) Basidiomycota: Club Fungi Sexual reproduction is most common Basidiocarp: fruiting body Basidia: sites of sexual reproduction to produce basidiospores Gills: connected hyphae that support the basidia Fungi in Ecosystems Decomposition releases elements from dead matter back to food web Mutualistic relationships with animals, plants, and protists 90% of vascular plants have mycorrhizal partners to channel water and minerals from the soil to the plant Figure 24.25 Leaf-cutter ant. A leaf-cutter ant transports a leaf that will feed a farmed fungus. (credit: Scott Bauer, USDA-ARS) Other Roles of Fungi Fermentation Antibiotics: penicillin and cephalosporins Medical drugs: immunosuppressant drug cyclosporine Model organisms: genetic research Lichen Not a single organism, but a mutualistic relationship between a fungus and an alga Algae: photosynthesis provides carbon and energy Fungus: provides minerals and protection from dryness and excessive light Neither can survive alone Soemtimes used to monitor air quality This cross-section of a lichen thallus shows the (a) upper cortex of fungal hyphae, which provides protection; the (b) algal zone where photosynthesis occurs, the (c) medulla of fungal hyphae, and the (d) lower cortex, which also provides protection and may have (e) rhizines to anchor the thallus to the substrate. Some fungal pathogens include (a) green mold on grapefruit, (b) powdery mildew on a zinnia, (c) stem rust on a sheaf of barley, and (d) grey rot on grapes. In wet conditions Botrytis cinerea, the fungus that causes grey rot, can destroy a grape crop. However, controlled infection of grapes by Botrytis results in noble rot, a condition that produces strong and much-prized dessert wines. (a) Ringworm presents as a red ring on skin; (b) Trichophyton violaceum, shown in this bright field light micrograph, causes superficial mycoses on the scalp; (c) Histoplasma capsulatum is an ascomycete that infects airways and causes symptoms similar to influenza. Human Fungal Infections Mycosis: disease caused by fungal infection ○ ○ Cannot be treated with antibiotics because antibiotics only work on prokaryotic cells Many antifungal medications have serious side effects due to similarity between eukaryotic cells Valley fever causes symptoms similar to TB Candida causes oral thrush and vaginosis Opportunistic fungal infections take advantage of compromised immune systems ○ Histoplasmosis can kill HIV patients Humungous Fungus Armillaria ostoyae, honey mushroom, causes root disease in conifers 2384 acres of soil in Oregon ○ 1665 football fields or 4 square miles 2400 – 8600 years old FIMS Hypothesis Cretaceous-Paleogene extinction event – caused by asteroid impact Dinosaurs and many other species went extinct Rise of the mammals – Why not a second reptilian era? ○ Selective advantage for endothermic animals Constant body temperature → ability to forage, digest, and reproduce More complex immune system → fight off fungal infections Protection of embryos Fungi Activity https://youtu.be/V4m9SefyRjg?si=O-B3UTj1g7xCuiEq 4 minutes