Lecture #4

1. Lecture #4 Fungi

3. “The Mighty Mushroom” • take a walk through a forest • mushrooms are truly are the largest organisms in the forest • Kingdom Fungi: • not just mushrooms! • approximately 100,000 species now described • may be as many as 1.5 million species • range from unicellular to complex multicellular organisms • just about every terrestrial and aquatic environment • essential decomposers in ecosystems • critical for the release of nutrients into the ecosystem • included with animals and choanoflagellates in clade Opisthokonta • diverged about a billion years ago

4. Nutrition • like animals, fungi are heterotrophs • cannot make their own food like algae and plants • unlike animals – they do not ingest their food • fungi absorb nutrients from its environment • many fungi secrete powerful hydrolytic enzymes that breakdown complex organic compounds into smaller ones that can be absorbed • others use enzymes to penetrate the walls of cells – absorption • digestion of both living and dead sources

5. Body Structure Reproductive structure • most common body structures are: • 1. multicellular filaments • 2. yeasts • relatively few species grow as yeasts • those that do inhabit moist environments • most grow as multicellular filaments • body structure: • enhances their ability to absorb nutrients • formation of a network of tiny filaments called hyphae • hyphae form an interwoven mass called a mycelium • a mycelium infiltrates the material on which it feeds • 1cm3 of soil may have as much as 1 km of hyphae in a mycelium • mycelia grow very fast – nutrients for growth are carried rapidly via cytoplasmic streaming to the growing hyphae • grow from the tip • “spitzenkorper” – membrane system of vesicles from the golgi that travel to the growing tip via the cytokeleton and exocytose their contents for the growth of the hyphal cell wall • the emphasis is on increasing mycelium length NOT width Hyphae Cell wall Cell wall Nuclei Pore Spore-producing structures Septum Nuclei Septate hypha Coenocytic hypha 20 µm Mycelium

6. Fungal Hyphae • singular = hypha • consist of tubular cell wall surrounding a plasma membrane and cytoplasm of the cell • cell wall is strengthened by chitin (not cellulose = plants) • nitrogen containing polysaccharide • strong yet flexible • hyphae is divided into individual cells by walls called septa • septa have relatively large pores • allow the passage of ribosomes, mitochondria and nuclei between cells • those that lack septa are called ceonocytic fungi • mycorrhizal fungi: fungi with mutually beneficial relationships between the fungus and plant roots • mycorrhiza= symbiotic relationship between a fungus and the root of a vascular plant • the hyphae are specialized = haustoria • these fungi improve the delivery of nutrients to the plant’s root – e.g. phosphate and nitrogen ions • plants supply the fungus with the organic materials it needs to survive • ectomycorrhizal fungi= sheaths of hyphae over the root • grow into the extracellular spaces of the root’s cortex • arbuscularmycorrhizal fungi = extend branching hyphae through the root cell wall via tubes • these haustoria remain separated from the plant by the plant’s plasma membrane! Cell wall Cell wall Nuclei Pore Septum Nuclei Plant cell wall Fungal hypha Septate hypha Coenocytic hypha Plant cell Plant cell plasma membrane Haustorium Haustoria

7. Reproduction Key Heterokaryotic stage Haploid (n) Heterokaryotic (unfused nuclei from different parents) • reproduction through the production of spores • spores are carried by wind or water • germination upon exposure to moisture to produce a new mycelium • sexual reproduction: consists of three stages – plasmogamy, karyogamy and meiosis • begins when hyphae from two mycelia release pheromones • bind to receptors on the opposite mating type – hyphae extends toward the source of the pheromones (i.e. towards each other) • the hyphae meet and fuse – hyphae of the same mating type cannot fuse • two cytoplasms fuse = plasmogamy • nuclei from these two “parental” fungi do not fuse right away – fungus is now called a heterokaryon (”different nuclei”) • some species – exchange of chromosomes and even crossing over – genetic variability • hours or decades later (!) the nuclei will fuse = karyogamy PLASMOGAMY (fusion of cytoplasm) Diploid (2n) KARYOGAMY (fusion of nuclei) Spore-producing structures Zygote • sexual reproduction: • karyogamy: life cycle stage of fusion of two haploid nuclei in fungi • production of a diploid zygote • meiosis follows – regenerating haploid spores • karyogamy and meiosis generate genetic variability • spores are dispersed to germinate and form a new mycelium SEXUAL REPRODUCTION Spores ASEXUAL REPRODUCTION Mycelium MEIOSIS GERMINATION GERMINATION Spore-producing structures Spores

8. 10 m Key Heterokaryotic stage Haploid (n) Heterokaryotic (unfused nuclei from different parents) • asexual reproduction: most fungi can reproduce sexually and asexually depending on nutrient availability • 20,000 species use only asexual reproduction • reproduce by growing as filamentous fungi that produce haploid spores • these species are informally known as molds if they form visible mycelia • other reproduce asexually by growing as single-celled yeasts • don’t produce spores – reproduction is by cell division or by budding off of the parental cell PLASMOGAMY (fusion of cytoplasm) Diploid (2n) KARYOGAMY (fusion of nuclei) Spore-producing structures Zygote SEXUAL REPRODUCTION Spores Parent cell ASEXUAL REPRODUCTION Mycelium MEIOSIS GERMINATION GERMINATION Spore-producing structures Spores Bud

9. Fungal Diversity Arbuscular mycorrhizal fungi Sac fungi Club fungi Zygote fungi Chytrids • descended from a unicelluar, aquatic flagellated protist • earliest lineages of fungus thought to possess flagella • some still have flagella – called chytrids • then moved to land – fossils of the earliest vascular land plants have fungal associations (mycorrhizea) • radiated into 5 Phyla • 1. Chytridiomycota • 2. Zygomycota • 3. Glomeromycota • 4. Ascomycota • 5. Basidiomycota Chytridiomycota Glomeromycota Basidiomycota Zygomycota Ascomycota

10. Hyphae 1. Phylum: Chytridiomycota • known as the chytrids • most primitive of the fungi • ubiquitous in lakes and soil • some species are decomposer (saprobes) • others are parasitic (protists, plants and animals) • diverged the earliest in fungal evolution • like other fungi - walls are made of chitin • also share many enzymes and metabolic pathways with other fungal groups • unique in that they have flagellated spores called zoospores • some exist as single cells, others form colonies with hyphae • do not have a true mycelium – fungal body is called a thallus • closely related to the zygomycete group of fungus • are considered a coenocytic fungus – no septal walls in their hyphae • extensions off the hyphae produce digestive enzymes for decomposition of their substrate

11. 1. Chytridomycota • asexual reproduction: production of diploid zoospores by mitosis • zoospores produced from a zoosporangium by mitosis • zoosporangium located at the tip of hyphae • swim to new areas and undergo mitotic growth • to form a new thallus (i.e. mycelium) • sexual reproduction: production of haploid zoospores by meiosis • zoosporangium that produce haploid zoospores by meiosis are called gametangia • gametangium – reproductive structure that produces and releases gametes • zoospores are of opposite mating type – “male” and “female” • female zoospore attracts the male • two gametes fuse into a zygote • motile and biflagellated • zygote forms a protective wall to become a dormant cyst • with favorable conditions – redevelops into a haploid thallus/mycelium Sexual Asexual

12. 2. Phylum: Zygomycota • 1,100 known species • diverse in lifestyles • fast-growing molds • other can be parasites • others can be commensal (neutral) symbiontforms with animals • e.g. Rhizopusstolonifer– black bread mold • typical of a zygomycete • mycelium forms as a spread of horizontal hyphae over the food – penetrates it and absorb the nutrients • hyphae are coenocytic – septa are found only where the reproduction cells are formed • spore dispersal through the air eventually passes it onto other substrates for continued growth

13. Key Haploid (n) Heterokaryotic (n + n) Diploid (2n) PLASMOGAMY Rhizopus growing on bread Mating type (+) Gametangia with haploid nuclei Mating type (–) 100 µm Young zygosporangium (heterokaryotic) SEXUAL REPRODUCTION Dispersal and germination Zygosporangium (heterokaryotic) KARYOGAMY Sporangia Diploid nuclei Sporangium ASEXUAL REPRODUCTION MEIOSIS Dispersal and germination Mycelium 50 µm • sexual reproduction:“parents” are mycelia with two mating types: “-” and “+” • two mating types of hyphae form extensions toward one another (pheromones) • 2 gametangia form between them – multiple haploid nuclei within each • undergo plasmogamy(cytoplasm fusion, no nuclear fusion yet) to produce a zygosporangium • said to be heterokaryotic – no nuclear fusion yet!! • zygosporangium thickens – remains resistant and dormant for months • favorable conditions – karyogamy occurs = diploid nuclei • followed by meiosis into haploid spores • from the cyst arises a sporangium (called a fruiting body) for the production of haploid spores • this is what we see as the black fuzziness on bread • http://academic.kellogg.edu/herbrandsonc/bio111/animations/0120.swf

14. Key Haploid (n) Heterokaryotic (n + n) Diploid (2n) PLASMOGAMY Rhizopus growing on bread Mating type (+) Gametangia with haploid nuclei Mating type (–) 100 µm Young zygosporangium (heterokaryotic) SEXUAL REPRODUCTION Dispersal and germination Zygosporangium (heterokaryotic) KARYOGAMY Sporangia Diploid nuclei Sporangium ASEXUAL REPRODUCTION MEIOSIS Dispersal and germination Mycelium 50 µm • asexual reproduction: spores develop within the sporangium/fruiting body and are dispersed through the air • if they land on moist food – germinate and grow into new mycelia which can continue to reproduce new sporangia and reproduce asexually • in poor conditions, these germinating mycelia will grow and undergo sexual reproduction • some species can aim their sporangium at the site of food (Pilobolus)

15. Pilobolus:zygomycete that lives in the dung of grass eating mammals • sends up a delicate tube topped with a water-filled clear vesicle and a black disc called the mitosporangium or sporangium • must disperse its spores away from the cow dung because the spore must be eaten by the cow and passed through its digestive system to continue its life cycle • does so through an explosive dispersal mechanism • the sporangium is exploded from the underlying vesicle • increases in osmotic pressure within the vesicle explodes it outward and disintegrates the sporangium on top – acts as a water cannon • this structure is also photosensitive – there is a light-sensing retina like disc within the vesicle which can track the light

16. The cup-shaped ascocarps (fruiting bodies) of Aleuriaaurantia give this species its common name: orange peel fungus. The edible ascocarp of Morchella esculenta, the succulent morel is often found under trees in orchards. 10 µm Neurospora crassa feeds as a mold on bread and other food (SEM). Tuber melanosporum is a truffle, an ascocarp that grows underground and emits strong odors. These ascocarps have been dug up and the middle one sliced open. 3. Phylum Ascomycota • cup fungus • 60,000 species • red, blue and green molds • also includes mildews • defined by the formation of a cup-like ascocarp • a sac-like reproductive structure containing asci that produce haploid spores following sexual union • edible portion of this fungus • e.g. morels and truffles • many found on decaying vegetation • also include the tree fungi • half the species associate with algae to form lichens • most are septate within their hyphae

17. 3. Phylum Ascomycota • mildews: general term of mildew means dicolorations and odors created by fungus • mildews are actually are parasitic fungi of plants • white powdery appearance • Clavicepspurpurea parasitizes rye and other grasses causing the disease ergotism • ergotism can result from eating infected grains and results in gangrene, psychotic delusions, nervous spasms, abortion and convulsions • known as St. Anthony’s fire • pharmacologic activities of ergot are due to lysergic acid diethylamide (LSD)

18. Key Haploid (n) Conidia; mating type (–) Dikaryotic (n + n) Diploid (2n) Dispersal Germination Mating type (+) ASEXUAL REPRODUCTION Mycelium PLASMOGAMY Ascus (dikaryotic) Mycelia Conidiophore Dikaryotic hyphae extended from ascogonium SEXUAL REPRODUCTION KARYOGAMY Germination Dispersal Diploid nucleus (zygote) Eight ascospores Asci Four haploid nuclei MEIOSIS Ascocarp • asexual reproduction: fungus produces a powdery structures called conidiophores • mitosis within these structure produces spores called conidia • conidia are produced at the tips of the conidiophores (zygomycotes – spores formed within a sporangia) • conidia carried by air currents to new locations • germination leads to specialized hyphae formation called haustoriae – penetrate the epidermis of leaves and absorb nutrients • eventual production of a new mycelium

19. Key Haploid (n) Conidia; mating type (–) Dikaryotic (n + n) Diploid (2n) Dispersal Germination Mating type (+) ASEXUAL REPRODUCTION Mycelium PLASMOGAMY Ascus (dikaryotic) Mycelia Conidiophore Dikaryotic hyphae extended from ascogonium SEXUAL REPRODUCTION KARYOGAMY Germination Dispersal Diploid nucleus (zygote) Eight ascospores Asci Four haploid nuclei MEIOSIS Ascocarp • sexual reproduction:conidia also involved in sexual reproduction • fusion of the hyphae from opposite mycelia mating types is followed by plasmogamy • results in a the formation of reproductive structures called ascogonia (singular = ascogonium) • from these ascogonia arise multiple dikaryotic hyphae • each hypha produces a dikaryoticascus(plural = asci) at its tip • dikaryotic = 2 nuclei in each ascus • within each individual ascus – karyogamy unites the 2 nuclei and meiosis follows to form 4 haploid nuclei • these nuclei divide ONCE to form a total of 8 ascosporeseach with a single nuclei • multiple asci become surrounded by a protective ascocarp(aggregation of hyphae) • ascospores are ejected from this ascocarp the long dikaryotic stage in these fungi allows for extensive genetic recombination Ascocarp

20. Maiden veil fungus (Dictyphora), a fungus with an odor like rotting meat Fly agaric (Amanita muscoria), a common species in conifer forests in the northern hemisphere Puffballs emitting spores Shelf fungi, important decomposers of wood 4. Phylum: Basidiomycota • club fungus • 30,000 species • includes the mushrooms, shelf fungi, molds and mycorrizhae, rusts and smuts • important decomposers of wood • saprophoricand parasitic species (rusts and smuts) • all are characterized by the formation of a basidium – club-shaped structure which is diploid and produces basidiospores • fruiting bodies are also called basidiocarpsandare the structures we call mushrooms, puffballs, toadstools, bracket fungus • toadstools = poisonous mushrooms • beneath the fruiting body are extensive mats of mycelia that feed on decaying vegetation – very long lived and dikaryotic • hyphae of the mycelium are septate and coenocytic at specific stages during their reproduction

21. The Common Mushroom pileus • the basidiomycotes include the common mushroom • basidium= “little pedestal” • note the cap (pileus) with the gills on the underside • the supporting stalk = stipe • fruiting body or basidiocarp = cap + stalk • as in the ascomycotes and its ascocarp – the basidiocarpis an aggregation of hyphae basidiocarp stipe stipe gills

22. Dikaryotic mycelium PLASMOGAMY Mating type (–) Mating type (+) Gills lined with basidia Haploid mycelia SEXUAL REPRODUCTION Basidiocarp (dikaryotic) Dispersal and germination Basidiospores Basidium with four appendages Basidia (dikaryotic) Basidium Basidium containing four haploid nuclei KARYOGAMY MEIOSIS Key Diploid nuclei Haploid (n) Dikaryotic (n + n) 1 µm Basidiospore Diploid (2n) • sexual reproduction: • like ascomycotes – basidiomycotes are heterothallic - + and – mating type hyphae • two haploid mating types undergo plasmogamy and a dikaryotic mycelium forms • very fast growing • these “children” hyphae crowd out the parents and are long lived • rain or temperature changes induce the dikaryotic mycelium to form the basidiocarp(mushroom) • still dikaryotic – no nuclear fusion yet (nuclei are still separated and are haploid) • basidiocarps can “sprout up” within hours in the rain • the gills of the basidiocarp become lined with dikaryotic cells called basidia • karyogamy occurs - within each basidiumtwo nuclei fuse • meiosis results in 4 haploid nuclei total per basidium • each haploid nuclei develops into a basidispore • the basidiospores are located at the tips of the basidium • basidiospores are released when mature and are carried by the wind – germinate into new mycelia which rapidly undergo more sexual reproduction basidiospores

23. spore center of mass sterigma water film around spore wall apiculus Spore dispersal in mushrooms center of mass moves Spore • basidiospore dispersal can be quite explosive – e.g. puffballs • basidiospore is attached to the gill via asterigma– area of attachment is called an apiculus • dispersal mechanism: • 1. air is humid between the gills and the spore is covered with a thin film of water • 2. the spore secretes a small amount of sugar at the apiculus - the sugar picks up the air moisture and the water condenses to form a drop • 3. the increasing size of the water droplet draws the spores center of mass toward the apiculus • the water drop eventually disappears into the water film around the spore wall • 4. the spore center of mass quickly turns away from the apiculusand the spore accelerates in that direction – spore dispersal • the spore drops down from the gills & air currents know carry the spore away from the mushroom water film water droplet increasing water droplet

24. Fungi as Decomposers • fungi are well-adapted decomposers of organic material • very good at decomposing the polysaccharides cellulose and lignin (plants & wood) • their decomposition makes available to ecosystems inorganic nutrients such as carbon, nitrogen and phosphate ions

25. Fungal Associations • fungi can form mutualistic relationships with plants, algae and animals • Fungal-Plant associations: formation of mycorrhizal associations with the roots of vascular plants • these fungi are called mycorrhizal • all plant species harbor symbiotic fungi called endophytes • these live harmlessly inside the leaves of plants • most as ascomycetes • benefit certain grasses and other non-woody plants by making toxins to deter herbivores • can also increase the plants tolerance to heat, drought or heavy metals • Fungal-Animal associations: some fungus share their digestive services with animals • assist in the breakdown of plant material • guts of cattle and other grazing mammals • some insects (termites and ants) can raise “farms”of fungi to aid in digestion – called farmer insects leaf cutter ants depend on fungi to convert plant material into something these ants can digest

26. A fruticose (shrub-like) lichen A foliose (leaf-like) lichen Crustose (crust-like) lichens Fungal Associations • Lichens: 25,000 species • fungus + green algae (or cyanobacteria) • produce a unique superorganism • each requires one another to colonize areas they wouldn’t be able to alone • algae provide organic compounds, the cyanobacteria fix nitrogen • algae nestle among the fungal hyphae • found from the arctic to the tropics • most reproduce asexually • asexual reproduction: • either through fragmentation propagates new lichens • or by the formation of soredia– small clusters of hyphae with embedded algae - may be carried by the wind to new locations • some sexual reproduction can occur through the formation of basidiocarps or ascocarps • types of lichens: • 1. Crustose lichens – grow as a crust on a surface • 2. Foliose lichens – leafy in appearance • 3. Fructicose lichens – shrublike with branching and intertwined fibrous parts Ascocarp of fungus Soredia Fungal hyphae Algal layer Algal cell Fungal hyphae 10 µm

27. Practical uses of Fungi • popular as foods – mushrooms and morels and puffballs • distinctive flavors of cheeses – blue cheeses – come from the fungi used to ripen them • soft drink industry uses Aspergillusto produce citric acid for colas • we use yeasts and their fermentative processes to produce alcohol from sugar • yeast fermentation is also used to produce carbon dioxide which is used in the “rising” of breads – Saccharomyces cerevisiae • use of Saccharo. yeasts in research labs is exploited to determine genetic mechanisms that are also present in higher eukaryotes • use of fungi to synthesize glycoproteins in large quantities (cannot be performed by bacteria – lack the enzymes needed) • fungi have medicinal value – ergot (poison) components can reduce high blood pressure and to stop bleeding after childbirth • some fungi produce antibiotics – penicillin produced by the ascomycetemold called Penicillium • the decomposing function of Phanerochaetechrysosporium is being studied in order to determine how to make paper pulp

28. Penicillin Staphylococcus Penicillium • fungal contamination of a bacterial plate – area surrounding the fungus is free of bacteria • fungus capable of producing anti-bacterial substances = antibiotics • penicillin found on rotting oranges & its antibacterial actions on Gram +ve bacteria first attributed to Alexander Fleming in 1928 • Fleming coined the term "penicillin" to describe the filtrate of a broth culture of the Penicillium mold • 1939, Australian scientist Howard Walter Florey and a team of researchers demonstrated the in vivo bactericidal action of penicillin • 1942: John Bumstead and Orvan Hess became the first in the world to successfully treat a patient using penicillin • mass-produced in 1944 upon discovery of structure (1940 - Dorothy Crowfoot Hodgkin) • World War II – penicillin saved an estimated 12-15% of lives. • difficulty of manufacturing large quantities of penicillin and by the rapid renal clearance of the drug necessitating frequent dosing • became common procedure to collect the urine from patients being treated so that the penicillin could be isolated and reused • penicillin is classified as a b-lactam antibiotic • works by inhibiting the formation of peptidoglycan cross links in the bacterial cell wall. • search for derivatives of penicillin : first major development was ampicillin with a broader spectrum of activity • further development: beta-lactamase-resistant penicillins including amoxocillin,flucloxacillin, dicloxacillin and methicillin • these penicillins are still ineffective against the methicillin-resistant Staphylococcus aureus strains Zone of inhibited growth

29. Yeasts • 1500 species of unicellular fungi • not a single taxonomic or phylogenic grouping • many species – divided up between Phylum Ascomycota & Phylum Basidiomycota • often a synonym for the species Saccharomyces cerevisiae • chemotrophs– convert carbohydrates into CO2 and alcohol (fermentation) • most species are either obligate aerobes (for cellular respiration) or anaerobic (fermentation) • are no species of obligate anaerobes • naturally occurring on skins of fruits & berries – even on the skin or epithelial linings of humans • Candida albicans- yeast infections • athelete’s foot • also found in guts of mammal and insects • e.g. bees and ants • even in deep sea environments • exist as either diploid or haploid forms • asexual reproduction through budding or mitosis – occurs in both haploid and diploid cells • sexual reproduction through the production of pheromones by two mating types • happens under stress – the haploid cells die, leaving the diploid cells to undergo meiosis to form spores of two haploid mating types- alpha and “a” types • alpha-factor pheromone is attracted to and binds the “a” type yeast – the a-factor pheromone is attracted to and binds the alpha type yeast • two yeast cells meet and fuse – karyogamy results in a diploid cell

30. Fungi as Pathogens • about 30% of the 100,000 species are parasites or pathogens • mostly of plants • e.g. cause of chestnut blight and pine pitch • e.g. 10 to 50% of world fruit harvest is lost to fungus • some that attack food crops produce human toxins • Aspergillus(ascomycete) contaminates grains and peanuts – secretes aflatoxins • Clavicepspurpurea(ascomycete) grows on rye plants – toxins cause ergotism • about 500 species parasitize animals • Batrachochytriumdendrobatidis(chytrid) has killed the extinction or decline of 200 frog species • infection by a fungal parasite = mycosis • skin mycoses include ring-link “ringworm” (ascomycetes) – known more commonly as “Athlete’s foot” • Candida albicans– normal inhabitant of the vaginal epithelium • can grow too rapidly under certain environmental changes – causes a “yeast infection” • systemic mycoses – caused by inhaled spores • can cause tuberculosis like symptoms