Fungi Biology PDF

Topic 7 Eukaryotic micro-organisms Part II: Fungi Fungi Eukaryotic microorganisms Fungal types: Unicellular: Yeasts (e.g. Saccharomyces cerevisiae) Multicellular (e.g. mushrooms, molds) Non-motile Usually live in moist- humid or aquatic environments Growth temperature: 2-20 OC Heterotrophs: absorb n...

Topic 7 Eukaryotic micro-organisms Part II: Fungi Fungi Eukaryotic microorganisms Fungal types: Unicellular: Yeasts (e.g. Saccharomyces cerevisiae) Multicellular (e.g. mushrooms, molds) Non-motile Usually live in moist- humid or aquatic environments Growth temperature: 2-20 OC Heterotrophs: absorb nutrients from their external environment Some are saprophytes (decomposers): obtain their nutrients from dead organic matter Fungi mushrooms Ascomycete mold Multicellular fungus yeast Fungal morphology Cell wall: consists of chitin Body structures: - Multicellular filaments - Unicellular fungi (yeasts) Dimorphism: - some fungal species (e.g. Blastomyces) can grow both as filaments or yeasts depending on their environmental conditions Yeasts (unicellular fungi) Usually form multicellular colonies Reproduce by sexual or asexual reproduction (e.g. budding) Example: Saccharomyces cerevisiae Saccharomyces cerevisiae Multicellular fungi Filamentous structure: consist of mycelia Filaments= hyphae Mycelia: networks of branched hyphae => aid nutrient absorption Hyphae types: 1.Septate = with septa - Most fungi have hyphae divided into cells by septa - Septa= rings of hyphae cell walls - Pores allow cell-to-cell movement of organelles 2.Coenocytic fungi (aseptate): lack septa - have a continuous cytoplasmic mass with hundreds or thousands of nuclei Multicellular fungi structure Reproductive structure Hyphae Spore-producing structures 60 m Mycelium Reproductive structure= Fruiting body Spore-producing structures= sporangia Figure 31.3 Multicellular fungi: hyphaetypes Nuclei Cell wall Cell wall Pore Septum (a) Septate hypha Nuclei (b) Coenocytic hypha Multicellular fungi morphology Aerial hyphae sporangia sporangia Sporangia= sporeproducing structures Rhizoid (vegetative) hyphae mycelium mycelium Mold mycelia on bread Fungal reproduction Fungi reproduce by sexual or asexualreproduction by producing spores Asexual reproduction: - Simple cell division (binary fission) - Budding: a new organism develops from an outgrowth (bud) that separates from the parentalcell Sexual reproduction: - Production of diploid zygote (2n) by fusion of 2 haploid (n) fungi (hyphae) Fungal reproduction The haploid (n) spores can be produced sexually or asexually - Sexual reproduction: from the zygote by meiosis(called sexual spores) Zygote (2n) meiosis spores (n) - Asexual reproduction: by mitosis (called asexualspores) Spore (n) mitosis spores (n) Germination: Under favorable conditions, spores grow back to the vegetative cell (fungal cell) Spore germination vegetative cell Asexual reproduction of fungi: budding Binary fission Budding Budding Fungal life cycle Figure 31.5-3 Key Haploid stages (n) Heterokaryotic stage PLASMOGAMY (cytoplasmic fusion) Heterokaryotic stage Diploid stages (2n) Spore-producing structures KARYOGAMY (nuclear fusion) Spores (n) Mycelium ASEXUAL REPRODUCTION GERMINATION SEXUAL REPRODUCTION GERMINATION Zygote MEIOSIS Plasmogamy= cytoplasmic fusion Spores (n) Karyogamy= nuclear fusion Heterokaryotic stage= non-fused nuclei from 2 different parents Sporangia= spore-producing structures (2n) Sexual Reproduction Fungal nuclei are normally haploid Exception: transient diploid stages formed during the sexual life cycles Sexual reproduction: fusion of hyphae from different mating types Fungi use sexual signaling molecules called pheromones to communicate their mating type Plasmogamy: the union of cytoplasm from two parent mycelia Heterokaryon: the mycelium in which the haploid nuclei from each parent coexist (they do not fuse right away) Karyogamy: fusion of the haploid nuclei => production of diploid cells Asexual Reproduction Yeasts: reproduce mostly asexually by simple cell division and budding Molds: produce haploid spores by mitosis (e.g. conidia) => form mycelia => Molds and yeasts are called deuteromycetes (imperfect fungi) Figure 31.6 Asexual reproduction in severalfungi Conidia: asexual spores Parent cell Bud Penicillium: a common mold (food decomposer) Saccharomyces cerevisiae (undergoing budding) Supergroup Unikonts Slime molds Amoebozoans Gymnamoebas Nucleariids Fungi Opisthokonts Choanoflagellates Animals Unikonta Entamoebas The Origin of Fungi Fungi, animals, and theirprotist relatives form the Opisthokonts clade (part of the Unicontssupergroup) OPISTHOKONTS Animals and Choanoflaggelates (protists) Nucleariids (protists) Fungi Chytrids Other fungi Opisthokonts Common Ancestor (protist) Figure 31.11 Hyphae 25 m Fungal hypha 25 m Chytrids (1,000 species) Fungal categories (phyla) Zygomycetes (1,000 species) Glomeromycetes (160 species) Ascomycetes (65,000 species) Basidiomycetes (30,000 species) Figure 31.11a 1. Chytrids (phylum Chytridiomycota) 25 m Hyphae Chytrids Zoospores: flagellated spores 2. Zygomycetes (phylum Zygomycota) Named after their characteristic zygosporangia Example: black bread mold Spore-producing structures: Sporangia: produce spores by asexual reproduction Zygosporangia: - contain sexually produced spores (by karyogamy and meiosis) - Resistant to freezing and drying => can survive under unfavourable conditions Figure 31.13e Zygomycetes bread mold Zygosporangium Sporangium Zygomycetes sporangia Zygomycetes spores sporangia Aerial hyphae Mycelium Zygosporangium hyphae 3. Glomeromycetes (phylum Glomeromycota) Glomeromycetes form arbuscular mycorrhizae Mycorrhizae: mutually beneficial relationships between fungi and plant roots Arbuscular mycorrhizal fungi: have specialized hyphae (called haustoria) that penetrate the cell walls of root cells Mutualistic relationship: mycorrhizal fungi deliver phosphate ions and minerals to plants Figure 31.15 Glomeromycetes (phylum Glomeromycota) 2.5 m Arbuscular mycorrhizae: formed by Glomeromycetes Figure 31.4 Mycorrhizal Fungi Fungal hypha Plant cell wall Plant cell Haustorium Plant cell plasma membrane 4. Ascomycetes (phylum Ascomycota) Ascomycetes can produce spores by both sexual and asexual reproduction Spore producing structures: 1.Asci: - produce sexual spores (ascospores) - located in the ascocarps (fruiting body) 2.Conidiophores: specialized hyphae that produce asexual spores (conidia) Fruiting body: multicellular structure (reproductive structure) which contains the spore-producing structures Example: the bread mold Neurospora crassa, morels and truffles 8 ascospores Ascomycetes Figure 31.16 Ascomycetes (sac fungi) Morchella esculenta, the tasty morel Tuber melanosporum, a truffle 5. Basidiomycetes (phylum Basidiomycota) Club fungi: characterized by a clublike structure called a basidium (transient diploid stage) Basidia: the spore-producing structures Basidia produce sexual spores (basidiospores) Basidiocarp: the fruiting body, has numerous basidia Βasidiocarp example: mushrooms (the fruiting body= reproductive structure of Basidiomycetes) Basidium Basidiospore Basidiomycetes Fungi function: multiple roles Fungi exhibit diverse lifestyles and interactions with other organisms: – Decomposers – Mutualists – Parasites 1. Fungi as Decomposers Decomposers: - produce enzymes to break down complex molecules(e.g. cellulose) and dead organic material into smaller organic compounds => Produce CO2, nitrogen fixation  Important role in the nutrient recycling between the livingand nonliving world  maintain ecological balance 2. Fungi as Mutualists Fungi form mutualistic relationships with plants, algae, cyanobacteria, and animals  Beneficial ecological effects Mutualistic relationships: - Fungi - plants : e.g. Mycorrhizae - Fungi - animals: in the digestive system - Fungi- microorganisms: in lichens - Lichens: symbiotic association between a photosynthetic microorganism (cyanobacterium/green alga) and a fungus (e.g. an ascomycete) Lichens Figure 31.23 A foliose (leaflike) lichen Crustose (encrusting) lichens A fruticose (shrublike) lichen Figure 31.24 Lichens Ascocarp of fungus 50 m Fungal Algal hyphae layer Fungal hyphae Algal cell 3. Pathogenic fungi 30% of known fungal species are parasites or pathogens (mostly plant pathogens) Some plant pathogenic fungi are also toxic to humans Pathogenic fungi: 1. Pathogenic Zygomycetes: - e.g. genera Μucor, Rhizopus, Absidia - cause skin and ear infections, bronchitispneumonia Pathogenic fungi 2. Pathogenic Ascomycetes: (A) Αspergillus flavus: - Produces mycotoxins such as aflatoxins - Infects peanuts and wheat - Αflatoxin B1: liver cancer (due to p53 mutations) (B) Claviceps purpurea: - infects cereals (e.g. rye) - Produces ergotamine and lysergic acid (precursors for LSD synthesis)  psychotropic effects (hallucinations, temporary insanity), convulsions, gangrene Aspergillus flavus: aflatoxin production Infected peanuts Infected corn Αflatoxin Β1 Livers of mice treated with increased quantities of Aflatoxin B1 (upper left: no treatment, bottom right: higher treatment) Claviceps purpurea Rye infected by Claviceps purpurea Εrgotamine Pathogenic fungi 3. Pathogenic Βasidiomycetes: - Amanita phalloides: poisonous mushrooms - contain lethal toxins (e.g. phalloidin, amanitin) α-amanitin: inhibits eukaryotic RNA pol II Phalloidin: inhibits F-actin polymerisation - Αmanita muscaria and Psilocybe cubensis: “magic mushrooms” = psychoactive mushrooms => cause hallucinations (psychotropic effects) Amanita phalloides: poisonous mushrooms Amanita muscaria: “magic mashrooms” Μycoses Mycoses: human fungal infections Major types of human mycoses: (1)Superficial- cutaneous mycoses (2)Subcutaneous mycoses (3)Systemic mycoses (4)Opportunistic mycoses Superficial and cutaneous mycoses Fungal infections of hair, nails, and skin Μicrosporum furfur:ascomycete that causes ringworm Ascomycete genera Trichophyton and Epidermophyton: cause athlete’s foot (ringworm of the foot) Nail infection Superficial/cutaneous mycoses Ringworm Athlete’s foot Subcutaneous mycoses Subcutaneous fungal infection due to trauma Chromomycosis: caused by fungi Hormodendrum pedrosoi, Hormodendrum compactum, Phialophora verrucosa Sporotrichosis: caused by fungus Sporotrichum schenckii Mycetoma: caused by fungi of the Aspergillus genus Systemic mycoses Fungal infection spread through the blood stream tovarious sites/organs of the body Commonly cause respiratory infections initially, then spreadto other organs Examples: - Coccidioidomycosis: caused by Coccidioides immitis => produces tuberculosis-like symptoms - Histoplasmosis: caused by Histoplasma capsulatum - Cryptococcosis: caused by Cryptococcus neoformans - Blastomycosis: caused by Βlastomyces dermatitidis - Geotrichosis: caused by Geotrichum candidum Systemic mycoses Geotrichosis Cryptococcus neoformans in infected tissue Coccidioidomycosis Blastomycosis Geotrichosis Opportunistic mycoses Caused by fungi that are part of our normal flora (saliva, skin, digestive system) – normally nonpathogenic Become pathogenic and cause infections only in immunosuppressed individuals Example: -yeast Candida albicans: causes candidiasis => mouth infection (thrush), skin infection, vaginal infection, etc Opportunistic mycoses: Candidiasis thrush Candida albicans Skin infection Industrial and Therapeutic Applications of Fungi Production of antibiotics:e.g. ascomycetes of genus Penicillium -Penicillium chrysogenum :produces penicillin (antibacterial antibiotic) -Penicillium griseofulvum: produces griseofulvin (antifungal antibiotic) Production of alcoholic beverages, bread and cheeses - e.g. the yeast Saccharomyces cerevisiae: - Production of enzymes used for alcohol fermentation => production of beer, wine, etc - Also used as baking yeast (CO2 production) Genetic engineering: - Example: insulin-like growth factor (IGF) can be produced in the fungus Saccharomyces cerevisiae - study of genes involved in human diseases Antibiotic production byfungi Agar plate Staphylococcus (confluent colonies) Penicillium colonies Zone of growth inhibition The fungus Penicilium chrysogenum produces penicillin which kills Staphylococcus => produces zone of inhibition of Staphylococcus growth around its colonies on nutrient agar Antibiotic production by fungi Penicillium chrysogenum colonies on nutrient agar Penicillium griseofulvum penicillin griseofulvin SUMMARY Fungal Phylum Distinguishing Features of Morphology and Life Cycles Chytridiomycota (chytrids) Flagellated spores (zoospores) Zygomycota (zygomycetes) Resistant zygosporangium as sexual stage Glomeromycota (arbuscular mycorrhizal fungi) Arbuscular mycorrhizae formed with plants Ascomycota (ascomycetes, or sac fungi) Sexual spores (ascospores) produced internally in sacs called asci; vast numbers of asexual spores (conidia) also produced Basidiomycota (basidiomycetes, or club fungi) Elaborate fruiting body (basidiocarp) containing many basidia that produce sexual spores (basidiospores) Summary: human pathogenic fungi Fungus name Disease Fungi group Αspergillus flavus Liver cancer Ascomycetes Claviceps purpurea Psychotropic effects (hallucination), convulsions, gangrene Ascomycetes Amanita phalloides Mushroom food poisoning (fatal) Basidiomycetes (poisonous mushrooms) Αmanita muscaria, Psilocybe cubensis Psychotropic effects Basidiomycetes (magic mushrooms) Μucor, Rhizopus, Absidia Zygomycetes Μicrosporum furfur Skin and ear infections, bronchopneumonia Ringworm (skin infection) Trichophyton, Epidermophyton Athlete’s foot (ringworm of the foot) Ascomycetes Ascomycetes Summary: human pathogenic fungi Fungus name Disease Fungi group Hormodendrum pedrosoi Hormodendrum compactum Phialophora verrucosa Chromomycosis (subcutaneous mycosis) Ascomycetes Sporotrichum Schenckii Sporotrichosis (subcutaneous mycosis) Ascomycetes Aspergillus Mycetoma (subcutaneous mycosis) Ascomycetes Coccidioides immitis Coccidioidomycosis (systemic mycosis) Ascomycetes Histoplasma capsulatum Histoplasmosis (systemic mycosis) Ascomycetes Cryptococcus neoformans Cryptococcosis (systemic mycosis) Ascomycetes Βlastomyces dermatitidis Blastomycosis (systemic mycosis) Ascomycetes Geotrichum candidum Geotrichosis (systemic mycosis) Ascomycetes Candida albicans Candidiasis (opportunistic mycosis) Ascomycetes SBA example Which fungal phylum do mushrooms belong to? A. B. C. D. E. Ascomycetes Basidiomycetes Chytrids Glomeromycetes Zygomycetes SBA example What infection does Cryptococcus neoformans cause? A. B. C. D. E. Coccidioidomycosis Histoplasmosis Cryptococcosis Blastomycosis Geotrichosis