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. LE 31-2
Reproductive structure
Hyphae
Spore-producing
structures
20 µm
Mycelium

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

10. Cell wall Cell wall Nuclei Pore Septum Nuclei Septate hypha
Coenocytic hypha

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

12. LE 31-4
Hyphae
25 µm
Nematode
Hyphae adapted for trapping and killing prey
Plant
cell
wall
Fungal hypha
Plant cell
Plant cell
plasma
membrane
Haustorium
Haustoria

13. 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

14. 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

15. LE 31-5–3 Key Haploid (n) Heterokaryotic stage Heterokaryotic
(unfused nuclei from
different parents)
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

16. 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

17. 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

18. 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

19. LE 31-6
2.5 µm

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

21. LE 31-7
10 m
Parent
cell
Bud

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

23. 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

24. 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

25. LE 31-8
50 µm

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

27. 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

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

29. Chytrids
Chytrids (phylum Chytridiomycota) are found in freshwater and terrestrial habitats
They can be saprobic or parasitic
Molecular evidence supports the hypothesis that chytrids diverged earliest in fungal evolution
Chytrids are unique among fungi in having flagellated spores, called zoospores

30. LE 31-10
25 µm
Hyphae
Flagellum
4 µm

31. Video: Allomyces Zoospore Release
Video: Phlyctochytrium Zoospore Release

32. 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

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

34. 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

35. LE 31-12 Key PLASMOGAMY Rhizopus growing on bread Mating type (+)
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)
Sporangia
KARYOGAMY
Diploid
nuclei
Sporangium
ASEXUAL
REPRODUCTION
MEIOSIS
Dispersal and
germination
Mycelium
50 µm

36. 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

37. LE 31-13
0.5 mm

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

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

40. 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

41. LE 31-15
2.5 µm

42. 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

43. 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).

44. 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

45. LE 31-17 Key Conidia; Haploid (n) 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
Germination
KARYOGAMY
Dispersal
Diploid nucleus
(zygote)
Asci
Eight
ascospores
Four
haploid
nuclei
MEIOSIS
Ascocarp

46. 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

47. 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

48. 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

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

51. LE 31-20 Dikaryotic PLASMOGAMY mycelium Mating type (–) Mating
Haploid
mycelia
Gills lined
with
basidia
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)
1 µm
Basidiospore
Dikaryotic (n + n)
Diploid (2n)

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

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

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

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

57. 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”

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

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

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

62. LE 31-24 Ascocarp of fungus Soredia Fungal hyphae Algal layer
Algal cell
Fungal hyphae
10 µm

63. 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

64. LE 31-25 Corn smut on corn Tar spot fungus of sycamore leaves
Ergots on rye

65. 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

66. LE 31-26
Staphylococcus
Penicillium
Zone of
inhibited
growth