1. Chapter 31
Fungi

2. Overview: Mighty Mushrooms
Fungi are diverse and widespread
They are essential for the well-being of most terrestrial ecosystems because they break down organic material and recycle vital nutrients

4. Concept 31.1: Fungi are heterotrophs that feed by absorption
Despite their diversity, fungi share key traits, most importantly the way in which they derive nutrition

5. Nutrition and Fungal Lifestyles
Fungi are heterotrophs but do not ingest their food
They secrete exoenzymes that break down complex molecules, and then they absorb the smaller compounds

6. Fungi exhibit diverse lifestyles:
Decomposers
Parasites
Mutualistic symbionts

7. Animation: Fungal Reproduction and Nutrition
Body Structure
The morphology of multicellular fungi enhances their ability to absorb nutrients
Fungi consist of mycelia, networks of branched hyphae adapted for absorption
Most fungi have cell walls made of chitin
Animation: Fungal Reproduction and Nutrition

8. Some fungi have hyphae divided into cells by septa, with pores allowing cell-to-cell movement
Coenocytic fungi lack septa

9. Some unique fungi have specialized hyphae that allow them to penetrate the tissues of their host

10. Mycorrhizae are mutually beneficial relationships between fungi and plant roots
Ectomycorrhizal fungi form sheaths of hyphae over a root and also grow into the extracellular spaces of the root cortex
Endomycorrhizal fungi extend hyphae through the cell walls of root cells and into tubes formed by invagination of the root cell membrane

11. Concept 31.2: Fungi produce spores through sexual or asexual life cycles
Fungi propagate themselves by producing vast numbers of spores, either sexually or asexually

12. Sexual Reproduction Plasomogamy is the union of two parent mycelia
In many fungi, the haploid nuclei from each parent do not fuse right away; they coexist in the mycelium, called a heterokaryon
In some fungi, the haploid nuclei pair off two to a cell; such a mycelium is said to be dikaryotic

13. Hours, days, or even centuries may pass before the occurrence of karyogamy, nuclear fusion
During karyogamy, the haploid nuclei fuse, producing diploid cells
The diploid phase is short-lived and undergoes meiosis, producing haploid spores

14. Asexual Reproduction
In addition to sexual reproduction, many fungi can reproduce asexually
Many of these species grow as mold, sometimes on fruit, bread, and other foods

15. LE 31-6
2.5 µm

16. Other fungi that can reproduce asexually are yeasts, which inhabit moist environments
Instead of producing spores, yeasts reproduce asexually by simple cell division

17. LE 31-7
10 m
Parent
cell
Bud

18. Many molds and yeasts have no known sexual stage
Mycologists have traditionally called these deuteromycetes, or imperfect fungi

19. Concept 31.3: Fungi descended from an aquatic, single-celled, flagellated protist
Systematists now recognize Fungi and Animalia as sister kingdoms
In other words, fungi and animals are more closely related to each other than they are to plants or other eukaryotes

20. The Origin of Fungi
Molecular evidence supports the hypothesis that fungi and animals diverged from a common unicellular, flagellated ancestor
Fungi probably evolved before the colonization of land by multicellular organisms
The oldest undisputed fossils of fungi are only about 460 million years old

21. LE 31-8
50 µm

22. The Move to Land
Fungi were among the earliest colonizers of land, probably as symbionts with early land plants

23. Concept 31.4: Fungi have radiated into a diverse set of lineages
Fungi phylogeny is the subject of much research
Molecular analysis has helped clarify evolutionary relationships between fungal groups, although areas of uncertainty remain

24. LE 31-9 Zygote fungi Arbuscular mycorrhizal fungi Sac fungi Club fungi
Chytrids
Chytridiomycota
Zygomycota
Glomeromycota
Ascomycota
Basidiomycota

25. Chytrids
Chytrids (phylum Chytridiomycota) are found in freshwater and terrestrial habitats
They can be saprobic or parasitic
Chytrids are unique among fungi in having flagellated spores, called zoospores

26. Video: Allomyces Zoospore Release
Video: Phlyctochytrium Zoospore Release

27. Until recently, systematists thought that fungi lost flagella only once in their evolutionary history
Molecular data indicate that some “chytrids” are actually more closely related to another fungal group, the zygomycetes

28. Zygomycetes and other chytrids
LE 31-11
Glomeromycetes,
ascomycetes, and
basidiomycetes
Zygomycetes and other chytrids
Some
chytrids
Key
Common ancestor
Loss of
flagella

29. Zygomycetes
The zygomycetes (phylum Zygomycota) exhibit great diversity of life histories
They include fast-growing molds, parasites, and commensal symbionts
The zygomycetes are named for their sexually produced zygosporangia
The life cycle of black bread mold (Rhizopus stolonifer) is fairly typical of the phylum

30. Zygosporangia, which are resistant to freezing and drying, can survive unfavorable conditions
Some zygomycetes, such as Pilobolus, can actually “aim” their sporangia toward conditions associated with good food sources

31. LE 31-13
0.5 mm

32. Microsporidia
Microsporidia are unicellular parasites of animals and protists
They are now classified as zygomycetes

33. LE 31-14
10 µm
Host cell
nucleus
Developing
microsporidian
Spore

34. Glomeromycetes
The glomeromycetes (phylum Glomeromycota) were once considered zygomycetes
They are now classified in a separate clade
Glomeromycetes form a distinct type of endomycorrhizae called arbuscular mycorrhizae

35. Ascomycetes
Ascomycetes (phylum Ascomycota) live in marine, freshwater, and terrestrial habitats
The phylum is defined by production of sexual spores in saclike asci, usually contained in fruiting bodies called ascocarps
Ascomycetes vary in size and complexity, from unicellular yeasts to elaborate cup fungi and morels

36. LE 31-16
The cup-shaped ascocarps (fruiting bodies) of Aleuria aurantia 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
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.
Neurospora crassa feeds as a mold on bread and other food (SEM).

37. Ascomycetes reproduce asexually by enormous numbers of asexual spores called conidia
Conidia are not formed inside sporangia; they are produced asexually at the tips of specialized hyphae called conidiophores

38. Basidiomycetes
Basidomycetes (phylum Basidiomycota) include mushrooms and shelf fungi
The phylum is defined by a clublike structure called a basidium, a transient diploid stage in the life cycle

39. LE 31-18
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

40. The life cycle of a basidiomycete usually includes a long-lived dikaryotic mycelium
In response to environmental stimuli, the mycelium reproduces sexually by producing elaborate fruiting bodies call basidiocarps
Mushrooms are examples of basidiocarps

42. The numerous basidia in a basidiocarp are sources of sexual spores called basidiospores
Asexual reproduction is much less common in basidiomycetes than in ascomycetes

43. Concept 31.5: Fungi have a powerful impact on ecosystems and human welfare

44. Decomposers Fungi are efficient decomposers
They perform essential recycling of chemical elements between the living and nonliving world

45. Symbionts
Fungi form symbiotic relationships with plants, algae, and animals
All of these relationships have profound ecological effects

46. Mycorrhizae
Mycorrhizae are enormously important in natural ecosystems and agriculture
They increase plant productivity
RESULTS
RESULTS

47. Fungus-Animal Symbiosis
Some fungi share their digestive services with animals
These fungi help break down plant material in the guts of cows and other grazing mammals
Many species of ants and termites use the digestive power of fungi by raising them in “farms”

48. Lichens
Lichens are a symbiotic association of millions of photosynthetic microorganisms held in a mass of fungal hyphae

49. LE 31-23 A fruticose (shrub-like) lichen A foliose (leaf-like) lichen
Crustose (crust-like) lichens

50. The fungal component of a lichen is most often an ascomycete
Algae or cyanobacteria occupy an inner layer below the lichen surface

51. Pathogens
About 30% of known fungal species are parasites, mostly on or in plants
Animals are much less susceptible to parasitic fungi than are plants
The general term for a fungal infection in animals is mycosis

52. Practical Uses of Fungi
Humans eat many fungi and use others to make cheeses, alcoholic beverages, and bread
Genetic research on fungi is leading to applications in biotechnology
Antibiotics produced by fungi treat bacterial infections