Fungi: A Comprehensive Overview of Molds, Mildews & Mushrooms

1. Molds, mildews, & mushrooms An introduction to fungi

2. Fungi • Significant group of organisms – both basic and applied biology • Large Kingdom – • 80,000-120,000 species described • Estimated to be 1.5 million species • We will briefly survey the fungi and related organisms

3. Roles of fungi • Pathogens of plants and animals • Symbionts with plants and animals • Decomposers of organic matter • Deterioration of substances – wood, paper, grain, foods • Food and food products • Toxins and allergens • Myths & Religions • Tools in biology

4. Plant pathogens • Fungi are major pathogens of plants – cause great deal of damage to crops Example: Wheat rust • Major losses in yields of wheat • Romans had a god of rust - Robigus • In Southeastern US • Wheat rust severe, can’t grow wheat • Corn replaced wheat • cornbread, bourbon

5. Coffee rust epidemic in Ceylon

6. Irish potato famine • Potato imported to Europe in 1500’s, became a staple • Several years of favorable weather lead to epidemic of late blight of potatoes • Caused the Irish potato famine – mid 1800’s

7. Late blight of potato • Caused by Phytophthora infestans • No longer considered a true fungus

8. Fungal diseases of animals & humans • Generally less widespread than diseases caused by bacteria and viruses (exception – athletes foot), but can be severe • Certain diseases endemic to geographic areas – e.g. valley fever caused by Coccidioides sp. in the desert SW • Incidence of human mycoses is on the increase with use of immunosuppresant drugs and AIDS

9. Fungi as symbionts • Mycorrhizal association is very common among plants • Lichens

10. Fungi as decomposers • Important agents in the flow of energy and cycling of nutrients in biosphere • Decomposition particularly of plant litter • Food for higher trophic levels

11. Fungi as agents of deterioration • Cause deterioration of organics –food, wood, clothing, leather • Variety of antifungal products developed

12. Food and food supplements • Yeast – bread and alcohol • Mushrooms • Fermentation of plant products (soybeans) – soya sauce, tempeh, miso tofu,etc.

13. Mycotoxins • Produced by microfungal species on different stored food products • Aflatoxin produced by Aspergillus flavus

14. Allergens • Spores present in outdoor & indoor air • Sick building syndrome • Stachybotrys

15. Myths & Religions • Hallucigenic mushrooms

16. Used as model systems in biology • Neurospora crassa – 1 gene – 1 enzyme • Saccharomyces • Aspergillus

17. Major characteristics of fungi • Eukaryotic • Heterotrophic • Osmotrophs • Modular organisms – indeterminate growth • Multinucleate • Generally surrounded by cell wall • Generally nonmotile (some produce motile cells) • Most form spores as reproductive units

18. Fungal biology • Fungal body = thallus • Vegetative (somatic) phase – absorbs and assimilates nutrients, grows • Reproductive phase - all or part of thallus may differentiate to form reproductive structures – spores • Asexual (mitosis) or sexual reproduction (meiosis, fertilization)

19. Vegetative thallus • Variable – but most fungi form a branching network of multinucleate filaments • Filament = hypha (pl. hyphae) • Exceptions – yeasts, some lower fungi

20. Mycelium = filamentous fungal thallus • All hyphae in a thallus form the mycelium

21. Largest mycelia • Armillaria bulbosa – fungus humongous • 30 acres, 10 tons, 1500 years old

22. Hyphae • Walled tubes that contain cytoplasm • Eukaryotic – nuclei, mitochondria, ER, etc • Grow at tip • Form lateral branches that grow at tip

23. Basic types of hyphae • Aseptate hyphae – lack crosswalls, found in lower fungi • Septate hyphae – crosswalls divide hyphae into compartments, are incomplete, found in higher fungi

24. For filamentous fungi • What is a cell? • Not typical with one nucleus controlling a defined volume of cytoplasm, many nuclei occur together • Have age transitions – tip is young with senescent cytoplasm away from the tip • What is an individual? Hyphae from two individuals may fuse • two or more  one Hyphal pieces may be separated from thallus • one  two or more

25. Basic structure of hyphae • Size – 2 μ m to 1 mm in diameter, • 5-10 μm most common • Surrounded by cell wall – gives hypha shape and prevents it from bursting from osmotic pressure • Cell walls composed primarily of polysaccharides with less than 10% proteins and lipids • Microfibrillar polysaccharides embedded in an amorphous matrix

26. Cell walls • Microfibrillar polysaccharides – in most fungi is chitin – polymer of N-acetyl glucosamine ( 1,4) • Chitin accounts for 5-60% of cell wall • Amorphous matrix contains a variety of polysaccharides – glucans, mannans

27. Fine structure of hyphae • Apical region of hyphal tip – typically 150-500 μm long. • Dense cytoplasm, rich in organelles, few vacuoles • Extreme tip (1-5 μm) contains many small vesicles (the apical vesicle cluster, AVC) – with light microscope = spitzenkörper (in sepatate hyphae only); no other organelles • Behind the apical region, vacuoles increase in number and size, lipid granules accumulate

28. Fungal hypha

29. Hyphal tip

30. Nuclei • Small (1-2 μm) • Nuclear envelope does not break down during division, chromosomes not distinct • In apical region there are 1-50 nuclei • Fungal DNA less complex than other eukaryotes - fewer repeated DNA segments compared to other eukaryotes (less than 10% compared to 35% in mammals)

31. Nuclei

32. Organelles • Mitochondria – elongate with platelike cristae • Endoplasmic reticulum – narrow membrane bound channels • Golgi – ringed cisternae not flattened stacks

33. Hyphal growth • Growth occurs at the tip • Grow in pulse of radiolabelled wall precusor • Vesicles also concentrated at tip – few other organelles in tip

34. Hyphal growth • Not the same as cellular growth • Filamentous fungi do not undergo cell division after cell has doubled in size • Duplication cycle (analogous to cell cycle) • Apical compartment grows to a particular length, nuclear division followed by formation of 1 to several septa

35. Hyphal branching

36. Hyphal branching

37. Carbon nutrition of fungi • All fungi are heterotrophic – obtain C from organic sources • In this regard, they are like animals, but • Absorb nutrients from environment, do not ingest food

38. Three modes of heterotrophy • Saprotrophs (saprophytes)– obtain C from non-living organic matter • Biotrophs – obtain C from living organic matter • Parasites • Symbionts • Necrotrophs – kill organisms and use C of dead bodies • Parasites • Facultative or obligate

39. Fungi and Plants • Originally fungi were classified with plants – nonmotile, have cell wall • Are also similar to plants in that they are modular organisms not unitary like animals • Modules in plants – buds and branch; in fungi – hyphal tips • Comparison of characteristics of modular with unitary organisms

40. Unitary vs modular organisms

41. Unitary vs modular organisms

42. Vegetative phase  Reproductive phase • After period of growth, differentiation may occur • Reproduction can be sexual or asexual • Functions of reproduction • Recombination of genetic information • Propagation and dispersal of fungus • Dormancy – dispersal through time

43. Asexual reproduction • Fragmentation of thallus • Production of asexual spores (two main types) • Sporangiospores – develop within a sporangium • Lower fungi • Conidium (pl. conidia) – formed externally at the tips of specialized hyphae • Higher fungi

44. Sporangiospores

45. Conidia

46. Sexual reproduction • Three events occur in sexual life cycle • Plasmogamy – union of two cytoplasms • Karyogamy – union of two nuclei • Meiosis – reduction division • (In most organisms plasmogamy and karyogamy occur close together – called syngamy or fertilization

47. Sexual life cycle • The three events lead to three phases based on nuclear condition • Haploid (1n) – one set of chromosomes per nucleus • Diploid (2n) – two sets of chromosomes per nucleus • Dikaryotic (n+n) – two sets of genes in separate nuclei • Vegetative phase may be any of the above

48. Sexual life cycle

49. Sexual reproduction • Spores are typically produced • May be produced after plasmogamy & karyogamy – diploid (zygospores) • May be produced after meiosis – haploid (meiospores)

50. Reproductive phases • Fungi may carry out sexual reproduction, asexual reproduction or both types • The sexual reproductive phase is the teleomorph (perfect phase) • The teleomorph is used in phylogenetic classification system • No problem for those species that reproduce sexually or both sexually and asexually – can identify and classify based on teleomorph