2 The Characteristics of Fungi Body formunicellularfilamentous (tube-like strands called hypha (singular) or hyphae (plural)mycelium = aggregate of hyphaesclerotium = hardened mass of mycelium that generally serves as an overwintering stage.multicellular, such as mycelial cords, rhizomorphs, and fruit bodies (mushrooms)
3 fruiting bodiesboth are composed of hyphaemycelium
4 The Characteristics of Fungi Heterotrophyic- 'other food'Saprophytes or saprobes - feed on dead tissues or organic waste (decomposers)Symbionts - mutually beneficial relationship between a fungus and another organismParasites - feeding on living tissue of a host
5 Heterotrophic by Absorption Fungi get carbon from organic sourcesHyphal tips release enzymesEnzymatic breakdown of substrateProducts diffuse back into hyphaeEnzymatic breakdownMost enzyme release (and absorption) at tipsProteins and other materials synthesized by the entire mycelium are channeled by cytoplasmic streaming to the tips of the extending hyphae.Nucleus hangs backand “directs”ProductsEnzymesProduct diffuses backinto hypha and is used
6 Hyphae Tubular Hard wall of chitin Crosswalls may form compartments (± cells)MultinucleateGrow at tipsChitin is the same material used by Arthropods (Insects, crabs, etc.) in their exoskeletonsaNuclei of fungi are hard to see without stains
7 Hyphal growth Hyphae grow from their tips Mycelium = extensive, feeding web of hyphaeMycelia are the ecologically active bodies of fungiThis wall is rigidOnly the tip wall is plastic and stretches
11 Mycorrhizae “Fungus roots” Mutualism between: Several kinds Fungus (nutrient & water uptake for plant)Plant (carbohydrate for fungus)Several kindsZygomycota – hyphae invade root cellsAscomycota & Basidiomycota – hyphae invade root but don’t penetrate cellsExtremely important ecological role of fungi!Half of the mushroom-forming fungi (basidiomycota) form mycorrhizas with treesSome people think that the spongy tissue in roots evolved as a place where fungi could invade to form early links with plants that helped them survive the harsh life on early earth
12 “Ecto” mycorrhizaeRussula mushroom mycorrhizae on Western Hemlock rootMycorrhiza cross sections4 of the regions where mycorrhizas are found are circled.These are “ecto” because the hyphae remain outside the root cells (though they extend inside the root)Fungal hyphae around root and between cells
13 Lichens “Mutualism” between Fungus – structure Alga or cyanobacterium – provides foodThree main types of lichens:Crustose lichens form flat crusty plates, e.g., on rocksFoliose lichens-leafy in appearance, although structures are not true leaves.Fruticose lichens-more finely branched and may hang down like beards from branches or grow up from the ground like tiny shrubs.Thallus is a plant-like body that doesn’t have roots, stems or leavesThallus doesn’t look like either partnerDual nature of thalli was not fully understood until early 1900’sFungus gives the name to the lichen (by agreement)Fungus usually, but not always, an Ascomycote (in 8+ independent orders)Algae green. If bluegreen bacteria present, lichens fix nitrogen (turn atmospheric nitrogen into amino acid nitrogen in proteins)
14 Lichen internal structure Lichens are nature’s biological monitors of pollution and air qualityThalli act like spongesSome species more sensitive to pollutionWhich species are present can indicate air qualityMost resistant species can also be analyzed for pollutants, including bioaccumulation of heavy metals and radioactive isotopesThe nature of lichen symbiosis is may also be described as mutual exploitation instead of mutual benefit.Lichens live in environments where neither fungi nor algae could live alone.While the fungi do not not grow alone in the wild, some (but not all) lichen algae occur as free-living organisms.If cultured separately, the fungi do not produce lichen compounds and the algae do not “leak” carbohydrate from their cells.In some lichens, the fungus invades algal cells with haustoria and kills some of them, but not as fast as the algae replenish its numbers by reproduction.Lobaria oregana prefers old-growth conifer canopies in forests with clean air.
16 Fungi are Spore-ific!!!Spores - asexual (product of mitosis) or sexual (product of meiosis) in origin.Purpose of SporesAllows the fungus to move to new food source.Resistant stage-allows fungus to survive periods of adversity.Means of introducing new genetic combinations into a population
17 Reproduce by spores Spores are reproductive cells Formed: Sexual (meiotic in origin)Asexual (mitotic in origin)Formed:Directly on hyphaeInside sporangiaFruiting bodiesFungi reproduce by releasing spores that are produced either sexually or asexually.The output of spores from one reproductive structure is enormous, with the number reaching into the trillions.Dispersed widely by wind or water, spores germinate to produce mycelia if they land in a moist place where there is food.Penicillium hyphae with conidiaPilobolus sporangiaAmanita fruiting body
18 Hyphal growth from spore germinatingsporeFungal mycelia can be huge, but they usually escape notice because they are subterranean.One giant individual of Armillaria ostoyae in Oregon is 3.4 miles in diameter and covers 2,200 acres of forest,It is at least 2,400 years old, and weighs hundreds of tons.(Actually noone has seen this of this extent – but cultures have been taken from soil over that area and all isolates have been found to be the same individual)Ten cubic centimeters of rich organic soil may have fungal hyphae with a surface area of over 300 cm2myceliumMycelia have a huge surface area
19 The Characteristics of Fungi Fungus is often hidden from view. It grows through its food source (substratum), excretes extracellular digestive enzymes, and absorbs dissolved food.Indeterminate clonal growth.Vegetative phase of fungus is generally sedentary.
20 The Characteristics of Fungi Cell wall present, composed of cellulose and/or chitin.Food storage - generally in the form of lipids and glycogen.Eukaryotes - true nucleus and other organelles present.All fungi require water and oxygen (no obligate anaerobes).Fungi grow in almost every habitat imaginable, as long as there is some type of organic matter present and the environment is not too extreme.Diverse group, number of described species is somewhere between 69,000 to 100,000 (of the estimated 1.5 million species total).
22 Molecular studies indicate that animals, not plants, are the closest relatives of fungi. Both Animals and Fungi are related most closely to a group of Protists known as the choanoflagellates (collar flagellates)Kingdom began in ocean during Precambrian (Late Proterozoic era)More than 100,000 species of fungi are known and mycologists estimate that there are actually about 1.5 million species worldwide.Evolution of the fungi
23 Classification & Phylogeny ascibasidiaThe phyla of fungi are determined by1. motility of spores2. nature of sexual stageFungi moved onto land with the plants in the Early PaleozoicMuch of the evolution of fungi was in conjunction with the evolution of plants and plant partsFor example, when roots evolved, fungi were there and helped (mycorrhizas)When wood evolved, fungi evolved to take advantage of itOther evolutionary changes related to animalszygosporangiaClassification & Phylogenymotile spores
24 Chytridiomycota – “chytrids” Simple fungiProduce motile spores - zoosporesMostly saprobes and parasites in aquatic habitats, e.g. those devastating amphibian populationsCould just as well be ProtistsChytridium growing on sporesClassified in CMR as true fungi (because of their molecular relationships)Remainder of the phyla are almost exclusively terrestrial (a few molds on wet plant material)Chytriomyces on pine pollen
25 Zygomycota – “zygote fungi” Sexual - zygosporangiaAsexual – common (sporangia – bags of asexual spores)Hyphae have no cross wallsGrow rapidlyDecomposers, pathogens, and some form mycorrhizal associations with plantsRhizopus on strawberriesMost of the 600 zygomycote, or zygote fungi, are terrestrial, living in soil or on decaying plant and animal material.Asexual reproduction in sporangiaOne zygomycote group form mycorrhizas, mutualistic associations with the roots of plants.Rhinocerebral zygomycosis
26 Sexual zygsporangium with one zygospore Asexual sporangium with spores insideLife cycle of Rhizopus, a saporobe that may be opportunistically infectious in humans
27 Ascomycota – “sac fungi” Sexual reproduction – ascus (asci)Asexual – commonCup fungi, morels, trufflesImportant plant parasites & saprobesYeast - SaccharomycesDecomposers, pathogens, and found in most lichensMycologists have described over 60,000 species of ascomycetes, or sac fungi.Ascomycota tend to grow from spore to spore in one year and relate well to living plant tissuesThere is diverse form in the growth and fruiting structures – yeasts to morels, many intermediate (and small)Asexual reproduction by conidia (externally produced, not in sporangia)Half of the Ascomycota form lichens (evolved 8 or more times in different orders) but not all lichens are AscomycotesA cluster of asci with spores
28 Sac fungi diversityThis begins the first of several photographic reviews of fungal diversity. Enjoy the pictures and try and get a feeling of some of the different forms these fungi take and their roles in the environment.
29 Basidiomycota – “club fungi” Sexual reproduction – basidiaAsexual – not so commonLong-lived dikaryotic myceliaRusts & smuts –plant parasitesMushrooms, polypores, puffballs, boletes, bird’s nest fungiEnzymes decompose wood, leaves, and other organic materialsDecomposers, pathogens, and some form mycorrhizal associations with plantsAsexual spores conidiaEcologically important on wood as decomposers and parasitesHalf the mushrooms form mycorrhizasSEM of basidia and spores
30 Mushroom Life Cycle haploid mycelium N 2N N+N Meiosis mycelium and fruitingbody are dikaryoticHyphal fusion of haploid myceliahaploid myceliumMushroom Life CycleN N N+NMeiosisNuclear fusion in basidiumyoung basidia - the only diploid cells
32 Some fungi have more than one scientific name – Why? Teleomorph: the sexual reproductive stage (morph), typically a fruiting body (e.g., Morchella esculenta, Agaricus brunescens).Anamorph: an asexual reproductive stage (morph), often mold-like (e.g. Aspergillus flavus, Fusarium solani). When a single fungus produces multiple morphologically distinct anamorphs, they are called synanamorphs.Holomorph: the whole fungus, including all anamorphs and the teleomorph.
33 Deuteromycota – Form Phylum “Imperfect Fungi” Fungi that seldom or never reproduce sexually.Asexual reproduction by vegetative growth and production of asexual spores common.
34 Yeasts Single celled fungi Adapted to liquids Plant saps Water films Moist animal tissuesBread and wine yeast, the budding yeast, SaccharomycesEasily cultured. For a time, this was the most important organism for studying the molecular genetics of eukaryotesThus, Saccharomyces is arguably the most important organism known to humansCandida causes diseases of humans, usually experiencing chemical imbalance or immune problemsCandidaSaccharomyces
35 Molds Rapidly growth Asexual spores Many human importances Food spoilageFood productsAntibiotics, etc.A mold is a rapidly growing, asexually reproducing fungus.The mycelia of these fungi grow as saprobes or parasites on a variety of substrates.Also used in foods (Blue cheese, Tempeh) and in industrial production of drugsEarly in life, a mold, a term that applies properly only to the asexual stage, produces asexual spores.Later, the same fungus may reproduce sexually, producing zygosporangia, ascocarps, or basidiocarpsSome molds go through a “fake sex” processNoble Rot - BotrytisAntibiotic activity
36 HUMAN-FUNGUS INTERACTIONS Beneficial Effects of FungiDecomposition - nutrient and carbon recyclingBiosynthetic factories. Can be used to produce drugs, antibiotics, alcohol, acids, food (e.g., fermented products, mushrooms)Model organisms for biochemical and genetic studiesHarmful Effects of FungiDestruction of food, lumber, paper, and clothAnimal and human diseases, including allergiesToxins produced by poisonous mushrooms and within food (e.g., grain, cheese, etc.)Plant diseases.