Lecture #4

1. Lecture #4 Fungi

2. “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 plants in the Clade Opisthokonta • diverged about a billion years ago

3. 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 • digestion of both living and dead sources

4. 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 called hyphae (hypha – singular) • each hypha consists of tubular cell wall surrounding a plasma membrane and cytoplasm of the cell • cell wall is strengthened by chitin (not cellulose = plants) • chitin - nitrogen containing polysaccharide • strong yet flexible Hyphae Spore-producing structures 20 µm Mycelium

5. Body Structure Reproductive structure • body structure: • hyphae enhances the ability to absorb nutrients • hyphae form an interwoven mass called a mycelium (mycelia plural) • 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 • 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 • septate hyphae are 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 Cell wall Cell wall Nuclei Pore Septum Nuclei Septate hypha Coenocytic hypha

7. Mycorrhizal Fungus • 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 = form haustoriathat project into a plant cell • but do not penetrate it • haustoriaremain separated from the plant by the plant’s plasma membrane! • a beneficial mutalistic relationship = symbiotic • can 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 • very common type - ectomycorrhizal fungi= sheaths of hyphae grow over the root • grow into the extracellular spaces between the cells of the plant’s root Plant cell wall Fungal hypha Plant cell Plant cell plasma membrane Haustorium Haustoria

8. 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 PLASMOGAMY (fusion of cytoplasm) • definitions: • karyogamy: fusion of two haploid nuclei in fungi • production of a diploid zygote • plasmogamy: fusion of the cytoplasm NOT the nuclei • produces a heterokaryotic stage – means different nuclei Diploid (2n) KARYOGAMY (fusion of nuclei) Spore-producing structures Zygote SEXUAL REPRODUCTION Spores ASEXUAL REPRODUCTION Mycelium MEIOSIS GERMINATION GERMINATION Spore-producing structures Spores

9. Sexual Reproduction Key Heterokaryotic stage Haploid (n) Heterokaryotic (unfused nuclei from different parents) • sexual reproduction: consists of three stages – plasmogamykaryogamy meiosis • begins when hyphae from two mycelia release pheromones • 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 PLASMOGAMY (fusion of cytoplasm) Diploid (2n) KARYOGAMY (fusion of nuclei) Spore-producing structures Zygote SEXUAL REPRODUCTION Spores ASEXUAL REPRODUCTION Mycelium MEIOSIS GERMINATION GERMINATION Spore-producing structures Spores

10. Sexual Reproduction Key Heterokaryotic stage Haploid (n) Heterokaryotic (unfused nuclei from different parents) • sexual reproduction: • hours or decades later (!) the nuclei will fuse = karyogamy • production of a diploid zygote • meiosis follows – producing haploid spores • karyogamy and meiosis generate genetic variability • spores are dispersed to germinate and form a new mycelium • mycelium can repeat sexual reproduction or undergo asexual reproduction PLASMOGAMY (fusion of cytoplasm) Diploid (2n) KARYOGAMY (fusion of nuclei) Spore-producing structures Zygote SEXUAL REPRODUCTION Spores ASEXUAL REPRODUCTION Mycelium MEIOSIS GERMINATION GERMINATION Spore-producing structures Spores

11. 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 • some species reproduce through their mycelium making 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

12. 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

13. Hyphae 1. Phylum: Chytridiomycota • known as the chytrids • most primitive of the fungi - diverged the earliest in fungal evolution • ubiquitous in lakes and soil • some species are decomposers • others are parasitic - on protists, plants and animals • 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 • are considered a coenocytic fungus – no septal walls in their hyphae • extensions off the hyphae produce digestive enzymes for decomposition of their substrate

14. 1. Chytridomycota • asexual reproduction: production of diploid zoospores by mitosis • hyphae tips develop into zoosporangia – production of zoospores by mitosis • zoospores swim to new areas and undergo mitotic growth • form a new thallus (i.e. mycelium) Sexual Asexual

15. 1. Chytridomycota • sexual reproduction: production of haploid zoospores by meiosis • zoosporangia of the thallus produce zoospores • zoospores develop into hyphae that produce gametes by meiosis • tips of these hyphae bear gametangia • gametangium= reproductive structure that produces and releases gametes • “male” and “female” gametes are flagellated and swim to each other • fuse into a zygote • motile and bi-flagellated • zygote forms a protective wall to become a dormant cyst • with favorable conditions – redevelops into a haploid thallus/mycelium Sexual THALLUS Asexual

16. 2. Phylum: Zygomycota • 1,100 known species • diverse in lifestyles • fast-growing molds • other can be parasites • others can be commensal (neutral) symbiotic forms 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

17. 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 hyphae or two mating types: “-” and “+” • + and – hypha extend toward one another (pheromones) • two gametangia form between these hyphae – each contains multiple haploid nuclei that are similar to gametes • two gametangia undergo plasmogamyto produce a zygosporangium • said to be heterokaryotic – no nuclear fusion yet!! • zygosporangium thickens – remains resistant and dormant for months • favorable conditions – karyogamy occurs in the zygosporangium= diploid nuclei following fusion • 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 • spores germinate into new + and - mycelia • http://academic.kellogg.edu/herbrandsonc/bio111/animations/0120.swf

18. 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)

19. 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 • the sporangium photosensitive – there is a light-sensing retina like disc within the vesicle which can track the light

20. 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 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

21. 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

22. 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 at the tip of their hyphae • mitosis within the conidiophore produces spores called conidia • in ascomycotes – spores formed within conidiophores • in 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 with new conidiophores e.g. Neurosporacrassa – bread mold

23. sexual reproduction:conidia also involved in sexual reproduction • fusion of the hyphae from opposite mycelia mating types is followed by plasmogamy (just like in the zygomycotes) • plasmogamy is followed by the development of reproductive structures called ascogonia (singular = ascogonium) • from these ascogonia arise multiple dikaryotic hyphae (2 unfused nuclei inside) • at the tip of each of these hyphae a dikaryoticascusforms (plural = asci) • within each individual ascus – karyogamy unites the 2 nuclei and meiosis followsto form 4 haploid nuclei • each of these 4 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) • this is what you can eat • ascospores are ejected from this ascocarp to germinate and form new mycelia Key Conidia; mating type (–) or (+) Haploid (n) Dikaryotic (n + n) Diploid (2n) Dispersal fusion of (+) and (-) hyphae Germination ASEXUAL REPRODUCTION Mycelium PLASMOGAMY Ascus (dikaryotic) the long dikaryotic stage in these fungi allows for extensive genetic recombination Mycelia Conidiophore Hyphae extending from ascogonium SEXUAL REPRODUCTION Germination KARYOGAMY Dispersal Diploid nucleus (zygote) Eight ascospores Asci Four haploid nuclei MEIOSIS Ascocarp

24. 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 • saprophoric (decomposing) and parasitic species (rusts and smuts)

25. 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 • all are characterized by the formation of a basidium– club-shaped structure which is diploid and produces basidiospores • fruiting bodies are also called basidiocarpsand are 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

26. 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

27. 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: • two haploid mating types ‘+’ and ‘–’ undergo plasmogamyand a dikaryotic mycelium forms • rain or temperature changes induce the dikaryotic mycelium to form the basidiocarp(mushroom) • still dikaryotic – no nuclear fusion yet • basidiocarps can “sprout up” within hours in the rain • the gills of the basidiocarpare lined with dikaryotic cells called basidia(basidium = singular) • within each basidiumkaryogamy occurs - two nuclei fuse • followed by meiosis 4 haploid nuclei total per basidium • at the tip of the basidium - each haploid nuclei develops into a basidiospore • basidiospores are released when mature and are carried by the wind – germinate into new mycelia which rapidly undergo more sexual reproduction basidiospores

28. 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 • 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 - the sugar picks up the air moisture and the water condenses to form a drop where the spore attaches to the gill • 3. the increasing size of the water droplet shifts spores center of mass • 4. the water drop eventually disappears into the water film around the spore wall • 5. the spore center of mass quickly shifts away and the spore dispersal in that direction • 6. the spore drops down from the gills & air currents know carry the spore away from the mushroom water film water droplet increasing water droplet

29. 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

30. Yeasts • 1500 species of unicellular fungi • not a single taxonomic or phylogenic grouping • divided up between Phylum Ascomycota & Phylum Basidiomycota • often a synonym for the species Saccharomyces cerevisiae • but there are several species of yeasts • are chemotrophs– convert carbohydrates into CO2 and alcohol (fermentation) • most species are either obligate aerobes (for cellular respiration) or anaerobic (fermentation) • naturally occurring on skins of fruits & berries – even on the skin or epithelial linings of humans • Candida albicans- yeast infections or athlete’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

31. Yeasts • 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” • 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 Haploid alpha a Diploid

32. 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 • 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 leaf cutter ants depend on fungi to convert plant material into something these ants can digest

33. Fungal Associations • 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

34. A fruticose (shrub-like) lichen A foliose (leaf-like) lichen Crustose (crust-like) lichens Fungal Associations: Lichens • Lichens: 25,000 species • fungus + green algae (or cyanobacteria) • 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 • 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

35. Lichens • asexual reproduction: • either through fragmentation • 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 Ascocarp of fungus Soredia Fungal hyphae Algal layer Algal cell Fungal hyphae 10 µm

36. 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

37. Penicillin Staphylococcus Penicillium • upon 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 • 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. Zone of inhibited growth

38. Penicillin • penicillin is classified as a b-lactam antibiotic • works by inhibiting the formation of peptidoglycan cross linksin 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

39. 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