Fungi

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Chapter 24
Lecture Outline
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2. A 460 million year old fossil fungus –
one of the oldest known
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3. 3
Chapter 24
Fungi
Chapter Outline:
 Evolutionary Relationships of the Kingdom Fungi
 Fungal Bodies and Feeding
 Fungal Asexual and Sexual Reproduction
 The Importance of Fungi in Ecology and Medicine
 Biotechnological Applications of Fungi

4.  Eukaryote supergroup Opisthokonta
 Includes certain protists, Kingdom Animalia, and Kingdom
Fungi
 Fungi are most closely related to animals, but diverged
over a billion years ago
 Fungi arose from protists related to Nuclearia – an amoeba
that feeds by engulfing cells
 True fungi are a monophyletic group of over 100,000
species
 Does not include slime molds or oomycetes
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Evolutionary Relationships
of the Kingdom Fungi

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Metazoa
(animal kingdom)
Choanoflagellates
(protists)
Nuclearia
(protist)
Chytrids
Microsporidia
Cryptomycota
Zygomycetes
AM fungi
Ascomycetes
Basidiomycetes
Septate hyphae,
dikaryotic hyphae,
fruiting bodies
Beneficial associations with
photosynthetic organisms
Critical innovations
KEY
Single flagellum
Rigid chitin
cell wall,
osmotrophic
nutrition
Primarily terrestrial habitat
Supergroup Opisthokonta
Kingdom Fungi

6. BIOLOGY PRINCIPLE
All species (past and present) are related
by an evolutionary history
There are more than 15 fungal phyla, but
their relationships and names are still being
determined.
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7. Fungal cell walls
 Rigid cell walls are composed of chitin
 A tough, nitrogen-containing carbohydrate
 Except for the cryptomycota which lack cell walls
 Benefit
 Allows cells to resist high osmotic pressure resulting
from feeding by absorption of small organic molecules
 Drawbacks
 Cells cannot engulf food due to rigid cell walls
 Restricts mobility of nonflagellated cells
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8. Seven main groups of fungi
 Cryptomycota
 Chytrids
 Microsporidia
 Zygomycetes
 AM fungi
 Ascomycetes
 Basidiomycetes
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9. Cryptomycota
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 The earliest-diverging fungi
 Occur in soil and water
 Can produce flagella for reproduction
 Only fungi to lack a cell wall

10. Chytrids
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 Microscopic
aquatic species
 Have cell walls
made of chitin
 Produce reproductive cells with flagella
 Only found in chytrids and cryptomycota
 Loss of flagella linked to ecological transition from
aquatic habitats to land

11. Zygomycetes
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 Several lineages
of terrestrial fungi
 Have distinctive large zygotes called zygospores
 ex: Common black bread molds

12. Microsporidia
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 Pathogens that
can only reproduce
inside the cells of
an animal host.
 Linked to honeybee decline
 Very small size (1–4 μm)
 Single-celled, chitin-walled spores
 Strong chitin wall helps survival in the environment
until they enter the bodies of animals

13. AM fungi
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 Arbuscular mycorrhizal
fungi
 Close symbiotic associations with plant roots
 Fungus provides plant with minerals
 Plant provides food for the fungus
 Fossils suggest that even early plants may have
depended on these AM fungal associations

14. Ascomycetes
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 Asci – unique reproductive structures
 Some ascomycetes cause disease
 Ecologically important as decomposers
 example: Edible truffles and morels

15. Basidiomycetes
 Basidia – club-shaped
reproductive cells
 Very important
decomposers
and plant symbionts
 ~30,000 species
 Varied reproductive structures
 Mushrooms, puffballs, stinkhorns, shelves, rusts, smuts

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17.  Fungi are most closely related to animals and
share several opisthokont features
 Both heterotrophic – cannot produce their own food
 Both use absorptive nutrition – secrete enzymes
and absorb small organic molecules
 Both store surplus food as the carbohydrate
glycogen
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Fungal Bodies and Feeding

18. Unique body form
 Most have mycelia composed of hyphae
 Most of the mycelium is diffuse and inconspicuous
 Fruiting bodies – visible reproductive structures
 Mushrooms are one type
 Fruiting bodies produce spores
 Spores
 Chitin-walled reproductive cells
 An adaptation to the terrestrial environment
 Transported by wind or by animals 18

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Region where hyphae mate,
forming a fruiting body
Mycelium
within substrate
(such as soil)
Mated hyphae
Fruiting body
above the
substrate
Spores
Unmated mycelium Different unmated mycelium

20. BIOLOGY PRINCIPLE
Living organisms grow and develop
After a mating process occurs,
mated hyphae produce fruiting bodies
whose form fosters spore production
and dispersal.
In suitable sites, spores
may germinate, producing
new mycelia.
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21. Distinctive growth processes
 Mycelia grow quickly when food is plentiful
 Grow from the edges as hyphae extend their tips
 Narrow dimensions and extensive branching
provides high surface area for absorption
 Osmosis important in growth – entry of water
produces force for tip extension
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23. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(a) Mycelium growing in liquid
medium
 Mycelium shape depends on substrate
 Long extensions in soil to reach food-rich areas
 Spherical in liquid medium
 Flat disk in petri dish
(b) Mycelium growing on flat,
solid medium
a: © Agriculture and Agri-Food Canada, Southern Crop Protection and Food Research
Centre, London ON; b: CDC

24.  Many fungi reproduce by microscopic spores
that grow into a new organism
 Spores may be asexual clones
 Or from sexual reproduction with new allele
combinations
 Asexual reproduction is ideal for rapid spread
 No need to find a mate
 No fruiting body
 No meiosis
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Fungal Asexual and
Sexual Reproduction

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 Conidia
 Asexual spores grown
at the tips of hyphae
 Aspergillus versicolor
 Causes skin and lung
infections in vulnerable
patients
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69 μm
© Dr. Dennis Kunkel Microscopy/ Visuals Unlimited

26.  Medically important fungi that reproduce
primarily by asexual means include
 Athlete’s foot fungus (Epidermophyton floccosum)
 Infectious yeast (Candida albicans)
 Budding yeast, Saccharomyces cerevisiae
 Can reproduce
either sexually
or by asexual
budding
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Daughter
cell (bud)
Mother cell
© Medical-on-Line/Alamy

27. Sexual reproduction
 Involves union of gametes, zygote formation and
meiosis
 Gametes of most fungi are cells from hyphal
branches
 Mating types differ biochemically
 Hyphal branches fuse between compatible
mating types
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28.  Most sexual organisms have plasmogamy
(fusion of gametes’ cytoplasm) followed by
karyogamy (fusion of gametes’ nuclei)
 In fungi, after plasmogamy, nuclei may remain
separate for a long time
 Mycelium is dikaryotic or heterokaryotic
 Some fungi persist as dikaryons, producing
clones that can live for hundreds of years
 Dikaryotic mycelia are functionally diploid
 Eventually, dikaryotic mycelia produce fruiting
bodies, the next stage of reproduction
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29. Fruiting bodies
 Mated mycelia will produce a fleshy fruiting body
when conditions are right
 Fruiting structure disperse haploid spores that grow
into mycelia
 If a haploid mycelium meets a compatible mating
type, they fuse (mate) and the cycle repeats
 Fruiting body structures aid spore dispersal
 Puffballs puff spores out onto wind currents
 Stinkhorns stink, and attract flies that carry off spores
 Truffles are underground – but their scent attracts
animals that dig them up 29

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(a) Fruiting bodies adapted for
dispersal of spores by wind
Spores
in a
sticky
matrix
(b) Fruiting body adapted for
dispersal of spores by insects
a: © Felix Labhardt/Taxi/Getty Images; b: © Bob Gibbons/ardea.com

31.  Decomposer fungi are essential components of
the Earth’s ecosystems
 Work with bacteria
 Only certain bacteria and fungi can break down
cellulose
 Release minerals to the soil and water
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The Importance of Fungi
in Ecology and Medicine

32. Fungal pathogens
 Crop diseases caused by 5000 species
 Rust spores can be spread on the wind
 Human diseases
 Dermatophytes – athlete’s foot, ringworm
 Pneumocystis jiroveci and Cryptococcus neoformans infect
people with weakened immune systems (as in AIDS)
 Blastomyces dermatitidis, Coccidioides immitis, and
Histoplasma capsulatum infect the lungs
 In nature, fungal pathogens play important ecological
role in controlling other species

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Puccinia
graminis
spores
Wheat leaf tissue
0.1 mm
(left): © Nigel Cattlin/Photo Researchers, Inc.; (right): © Herve Conge/ISM/Phototake

34. Beneficial fungal associations
 Fungal associations with photosynthetic
partners can be mutualistic
 Symbioses where both partners benefit
 Some animal species farm fungus for food
 Leaf-cutter ants, termites, beetles, salt marsh snail
 Mycorrhizal fungi associate with plant roots
 Lichens are partnerships between fungi and
photocynthetic algae or bacteria
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35. Mycorrhizae
 Association between the hyphae of certain fungi and the
roots of most seed plants
 More than 80% of terrestrial plants have mycorrhizae
 Plants receive increased supply of water and mineral
nutrients
 Fungi get organic food molecules from the plants
 Two most common types are endomycorrhizae (within
roots) and ectomycorrhizae (on roots)
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Seedling
root
Mycorrhizal
hyphae
© Dr. D.P. Donelley and Prof. J.R. Leake, University of Sheffield, Department of Animal & Plant Sciences

37.  Endomycorrhizae
 Fungal hyphae penetrate the spaces between root
cell walls and plasma membranes and grow along the
outer surface of the plasma membrane
 Arbuscular mycorrhizae (AM) form highly branched
structures with high surface area
37
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a: © Mark Brundrett
Hyphae
Arbuscules
Cell wall
Plasma
membrane
49 μm Root cells
(a) Micrograph of arbuscular mycorrhizae (b) Hyphae growing between cell walls
and plasma membranes

38.  Ectomycorrhizae
 Coat root surface and grow between cells of roots
 Some species of oak, beech, pine, and spruce trees
will not grow unless their ectomycorrhizal partners are
also present
Root
cells
38
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Ectomycorrhizal
hyphae coating
a root tip
Ectomycorrhizal
hyphae
(b) SEM of ectomycorrhizal hyphae (a) Ectomycorrhizal fruiting body (c) Hyphae invading intercellular spaces
a: © Jacques Landry, Mycoquebec.org; b: © Courtesy of Larry Peterson and Hugues Massicotte

39. EVOLUTIONARY CONNECTIONS
Comparison of genomes reveals how
basidiomycete metabolism diversified
 Basidiomycete genomes show diverse metabolic
pathways that help utilize organic carbon from plants
 Some decompose cellulose and lignin
 Break down dead trees, woody debris, leaf litter
 Some break down similar materials from animal dung
 Other species evolved ectomycorrhizal associations
with living plants
 What genes are different to give species different
capabilities?

40. EVOLUTIONARY CONNECTIONS
 White rot fungi – decompose both cellulose and lignin
 Complex enzymatic pathways to break down the many types of
chemical bonds
 Energetically expensive but give access to cellulose
 White rot fungal metabolism arose 300 mya during the
Carboniferous
 This new set of enzymes is why there are no major
plant carbon deposits since then!
 Brown rot fungi – break down cellulose, leave lignin
 Evolved from white-rot fungi but lost genes to degrade lignin,
saving energy by not producing those enzymes
 Ectomycorrhizal fungi evolved in turn from the
brown-rot fungi

41. Lichens
 Partnerships of particular fungi and certain photosynthetic
green algae and/or cyanobacteria
 25,000 lichen species
 Not all descended from a common ancestor
 At least five separate fungal lineages
 Three major forms – crustose, foliose, fruticose
 Photosynthetic partner provides organic food molecules
and oxygen
 Fungal partner provides carbon dioxide, water, and
minerals
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42. 42
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(a) Crustose lichen (b) Foliose lichen
(c) Fruticose lichen (d) Microscopic view of a cross
section of a lichen
a: © Joe McDonald/Corbis; b: © Lee W. Wilcox; c: © Ed Reschke/Getty Images; d: © Lee W. Wilcox

43.  Fungi convert inexpensive organic compounds into
citric acid, glycerol, and antibiotics
 Distinctive flavor of blue cheese
 Saccharomyces cerevisiae for bread, beer and wine
 Replace chemical procedures that generate harmful
waste products
 Wood pulp bleaching
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Biotechnological
Applications of Fungi