Mycology Lec. 2 د.خلود حمدان

Kingdom Fungi The characteristics of fungi The evolution of the fungi Fungal classification Fungal life cycles

The Characteristics of Fungi Body form unicellular filamentous (tube-like strands called hypha (singular) or hyphae (plural) mycelium = aggregate of hyphae sclerotium = hardened mass of mycelium that generally serves as an overwintering stage. multicellular, such as mycelial cords, rhizomorphs, and fruit bodies (mushrooms)

fruiting bodies both are composed of hyphae mycelium

The Characteristics of Fungi Heterotrophy - 'other food' Saprophytes or saprobes - feed on dead tissues or organic waste (decomposers) Symbionts - mutually beneficial relationship between a fungus and another organism Parasites - feeding on living tissue of a host.  Parasites that cause disease are called pathogens.

Hyphae Tubular Hard wall of chitin Crosswalls may form compartments (± cells) Multinucleate Grow at tips Chitin is the same material used by Arthropods (Insects, crabs, etc.) in their exoskeletonsa Nuclei of fungi are hard to see without stains

Hyphal growth Hyphae grow from their tips Mycelium = extensive, feeding web of hyphae Mycelia are the ecologically active bodies of fungi This wall is rigid Only the tip wall is plastic and stretches

Modifications of hyphae

Fungi as Saprobes and Decomposers

Fungi as Symbionts (Mutualism)

Fungi as Parasites & Pathogens

Fungi are Spore-ific!!! Spores - asexual (product of mitosis) or sexual (product of meiosis) in origin. Purpose of Spores Allows 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

Reproduce by spores Spores are reproductive cells Formed: Sexual (meiotic in origin) Asexual (mitotic in origin) Formed: Directly on hyphae Inside sporangia Fruiting bodies Fungi 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 conidia Pilobolus sporangia Amanita fruiting body

Hyphal growth from spore germinating spore Fungal 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 cm2 mycelium Mycelia have a huge surface area

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.

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 (estimated 1.5 million species total).

Classification & Phylogeny asci basidia The phyla of fungi are determined by 1. motility of spores 2. nature of sexual stage Fungi moved onto land with the plants in the Early Paleozoic Much of the evolution of fungi was in conjunction with the evolution of plants and plant parts For example, when roots evolved, fungi were there and helped (mycorrhizas) When wood evolved, fungi evolved to take advantage of it Other evolutionary changes related to animals zygosporangia Classification & Phylogeny motile spores

Chytridiomycota – “chytrids” Simple fungi Produce motile spores - zoospores Mostly saprobes and parasites in aquatic habitats Could just as well be Protists Chytridium growing on spores Classified 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 growing on pine pollen

Zygomycota – “zygote fungi” Rhizopus on strawberries Sexual Reproduction - zygosporangia Asexual reprod. – common (sporangia – bags of asexual spores) Hyphae have no cross walls Grow rapidly Decomposers, pathogens, and some form mycorrhizal associations with plants Most of the 600 zygomycote, or zygote fungi, are terrestrial, living in soil or on decaying plant and animal material. Asexual reproduction in sporangia One zygomycote group form mycorrhizas, mutualistic associations with the roots of plants. Rhinocerebral zygomycosis

Ascomycota – “sac fungi” Sexual Reproduction – asci (sing. = ascus) Asex. Reprod. – common Cup fungi, morels, truffles Important plant parasites & saprobes Yeast - Saccharomyces Decomposers, pathogens, and found in most lichens Mycologists 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 tissues There 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 Ascomycotes A cluster of asci with spores inside

Sac fungi diversity This 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.

Basidiomycota – “club fungi” Sexual Reproduction – basidia Asexual reprod – not so common Long-lived dikaryotic mycelia Rusts & smuts –plant parasites Mushrooms, polypores, puffballs, boletes, bird’s nest fungi Enzymes decompose wood, leaves, and other organic materials Decomposers, pathogens, and some form mycorrhizal associations with plants Asexual spores conidia Ecologically important on wood as decomposers and parasites Half the mushrooms form mycorrhizas SEM of basidia and spores

Deuteromycota – Form Phylum “Imperfect Fungi” Fungi that seldom or never reproduce sexually. Asexual reproduction by vegetative growth and production of asexual spores common.

Yeasts Single celled fungi Adapted to liquids Plant saps Water films Moist animal tissues Bread and wine yeast, the budding yeast, Saccharomyces Easily cultured. For a time, this was the most important organism for studying the molecular genetics of eukaryotes Thus, Saccharomyces is arguably the most important organism known to humans Candida causes diseases of humans, usually experiencing chemical imbalance or immune problems Candida Saccharomyces

Molds Rapidly growth Asexual spores Many human importances Food spoilage Food products Antibiotics, 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 drugs Early 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 basidiocarps Some molds go through a “fake sex” process Noble Rot - Botrytis Fig 31.21 Antibiotic activity

HUMAN-FUNGUS INTERACTIONS Beneficial Effects of Fungi Decomposition - nutrient and carbon recycling. Biosynthetic factories. Can be used to produce drugs, antibiotics, alcohol, acids, food (e.g., fermented products, mushrooms). Model organisms for biochemical and genetic studies. Harmful Effects of Fungi Destruction of food, lumber, paper, and cloth. Animal and human diseases, including allergies. Toxins produced by poisonous mushrooms and within food (e.g., grain, cheese, etc.). Plant diseases.