The eukaryotes : Fungi
Characteristics of fungi Eukaryotic Aerobic or facultatively anaerobic Chemoheterotrophic Require low pH, low moisture content Single cell (yeast) or multicellular Secrete antibiotics Cell wall composed of chitin Cell membrane contain sterol, glucan. Reproduce by sexual & asexual spores Some are internal or external parasites; a few are predators that capture prey Nonmotile Lack true roots, stems, & leaves Mycology is the study of fungi
Vegetative (non reproductive) Structures of Fungi Mold and fleshy fungi Thallus (Body) of a fungus made of tiny filaments or tubes called hyphae Hyphae contain cytoplasm & nuclei and has a cell wall of chitin In most molds hyphae contains cross walls called septa with pores to allow the movement of cytoplasm in hyphae. Septa divide them into distinct uninucleated cell like units. Hyphae with septa are called septate hyphae Hyphae without septa are called coenocytic hyphae Hyphae grow rapidly from the tips by cell division
Vegetative structure
Cross Walls of Hyphae Coenocytic hyphae where the nucleis of each cell is embedded in the cytoplasm without a cell wall Eg. Zygomycota, Oomycota Hyphae with cross walls Eg. Basidiomycota, Ascomycota
The portion of hypha involved in obtaining nutreients is called vegetative hypha and the portion concerned with reproduction is called reproductive hypha/aerial hypha. Hyphal networks are called mycelium, it is a filamentous mass formed under suitable environmental condition.
Yeast like fungi Nonfilamentous , unicellular fungi Typically spherical or oval shaped Facultative anaerobic Reproduce by budding or fission Mature buds separated from parent cell to give rise to new cell Buds fail to detach themselves from parent cell appears as chain like structure called pseudohypha.
Dimorphic fungi Most pathogenic fungi exhibit dimorphism i.e. two forms of growth. Such fungi can grow either a mold like or yeast like format. The mold like forms produce vegetativeand aerial hyphae and yeast like reproduce by budding. Condition Temperature dependent at37 they appear as yeast and at 25 they appear mold like appearance. Also changes with CO2 concentration On agar surface, Mucor rouxii exhibits yeastlike growth; in agar it is moldlike
Reproductive Structures Most fungi reproduce asexually & sexually Asexual reproduction produces genetically identical organisms Sexual reproduction in fungi occurs when nutrients or water are scarce In both case of sexual and asexual reproduction they form spores. Asexual spores : formed by hyphae , when they germinate produce daughter cell genetically identical to parents. Sexual spores: produced by fusion of nuclei of two opposite mating type
Asexual reproduction involving Binary fission –exponential growth to increase number Budding- form small outgrowth that enlarges to increase number Sexual reproduction involving Fusion of two opposite mating nuclei.
Asexual reproduction Asexual spores produced by an individual fungus through mitosis and subsequent cell division. Spores of asexual reproduction: Sporangiospore Conidiospore Chlamydospore
Conidiospore : produced in chains Two types Arthrospore : formed by fragmentation of separate hypha into single slightly thickened cells. Eg. Coccidioides immit Blastoconidia : consists of buds coming from parent cells Eg. Candida albicans
Arthrospore and Blastoconidia
Chlamydospore : A thick walled spore formed by rounding and enlargement of hyphal segment. Eg. Candida albicans
Sporangiospore : Formed within a sporangium or sac at the end of aerial hyphae Eg. Rhizopus
Sexual reproduction Sexual reproduction involve fusion of gametes, gametangia or hyphae. The process may involve only fusion of cytoplasm (plasmogamy) or fusion of nuclei (karyogamy) or production of meiotic spores (meiospores)
Plasmogamy Haploid donor cell nucleus (+) penetrates cytoplasm of recipient cell (–)
Karyogamy The + and – nuclei fuse Meiosis Diploid nucleus produces haploid nuclei (sexual spores)
Classification of Fungi Fungi are classified by their reproductive structures The 4 phyla of fungi are Basidiomycota, Zygomycota, Ascomycota, & Deuteromycota
Zygomycota sporangium fungi or common molds Includes molds & blights such as Rhizopus stolonifer (bread mold) Asexual reproductive structure called sporangium & produces sporangiospores Sexual spore produced by conjugation when (+) hyphae & (-) fuse is called zygospore
Basidiomycota Called club fungi Includes mushrooms, toadstools, puffballs, bracket fungi, shelf fungi, stinkhorns, rusts, & smuts Seldom reproduce asexually, some produce conidiospores. Basidium is sexual reproductive structure that make basidiospores
Ascomycota Called sac fungi Includes yeast, cup fungi, truffles, powdery mildew, & morels. Sac Fungi can reproduce both sexually and asexually Yeast reproduce asexually by budding (form small, bud-like cells that break off & make more yeasts) Asexual spores called conidia form on the tips of specialized hyphae called condiophores Ascocarp is specialized hyphae formed by parent fungi during sexual reproduction
Deuteromycota Sexual reproduction not yet observed. Recent suggestion is they are anamorphs i.e. lost their ability to reproduce sexually.
Fungus Life Cycle. Asexual reproduction involves germination of haploid spores, which divide by mitosis to produce hyphae. Hypha produces specific spores. Spores are released to continue the cycle. Sexual reproduction (perfect stage) begins when hyphae of different mating types fuse their cytoplasm in a process called plasmogamy, producing heterokaryotic cells with haploid nuclei. This is followed by karyogamy, or fusion of nuclei. The diploid zygote is short-lived and undergoes meiosis, producing haploid spores
Fungal Life Cycle
Fungal Life Cycle
Lichens Lichens are mutualistic symbiotic organisms. They have a fungus and a algal or cyanobacterial portion. Mutualistic combination of an alga (or cyanobacterium) & fungus Alga produces and secretes carbohydrates, fungus provides holdfast
Fruticose Crustose Foliose
Mycorrhizae Mycorrhizae means “fungus-root”; mutualistic relationship between plant and fungi The plant photosynthesizes while the fungus more efficiently takes up nutrients and water from the rhizosphere than the roots would alone. Fungi helps the plants by converting atmospheric nitrogen to ammonia to ensure nitrogen availability
Fungal Diseases (mycoses) • Systemic mycoses---------------Deep within body • Subcutaneous mycoses---------Beneath the skin • Cutaneous mycoses-------------Affect hair, skin, nails • Superficial mycoses-------------Localized, e.g., hair shafts • Opportunistic mycoses---------Caused by normal microbiota or fungi that are normally systemic, but can infect any tissue
Importance of fungi Fungal spores cause allergies Molds, mildew, rusts, & smuts damage crops Yeasts are used to make beer & bread Antibiotic penicillin Decomposers & recyclers of nutrients Mushrooms eaten as food Help form blue cheeses Aspergillus is used to make soy sauce Amanita is poisonous mushroom Can cause yeast infections