Fungi
- Explain how cellular structure in fungi
influences their growth processes.
- Differentiate among various
reproduction strategies in fungi.
- Compare and contrast the different
ecological associations that fungi
develop with other organisms.
- Summarize the unique and relevant
characteristics of the five fungal phyla. Understand why fungi are not classified
with plants.
- Understand how fungi are
fundamentally different from other living
organisms.
- Understand the reproductive
uniqueness of the fungi.
Defining Fungi
Mycologists believe
there may be as many
as 1.5 million fungal
species
Fungi are classified into
six main groups
-Chytrids
-Zygomycetes
-Glomeromycetes
-Ascomycetes
-Basidiomycetes
-Deuteromycetes
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• Fungi share characteristics
– Have different cell types
– Have chitin in their cell walls (rigid)
– Have dikaryon stage
– Undergo nuclear mitosis
• Fungi are closely related to animals
– Both heterotrophic – cannot produce their
own food
– Both use absorptive nutrition – secrete
enzymes and absorb resulting small organic
molecules
– Both store surplus food as the carbohydrate
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glycogen
General Biology
of the Fungi
Multicellular fungi
consist of long,
slender filaments
called hyphae
-Some
hyphae are
continuous
-Others are
divided by
septa
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General Biology of the Fungi
A mass of connected hyphae is called a
mycelium
-It grows through and digests its substrate
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Fruiting bodies are the visible
reproductive structures
Mushrooms are one type
Produce spores
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Rhizomorphs are fungal mycelia with the shape of roots to transport water
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General Biology of the Fungi
Cells walls of fungi are formed of
polysaccharides including chitin
-Cross-linked with proteins
Chitin is also found in the hard shells
(exoskeletons) of arthropods
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Distinctive growth processes
• Mycelia can grow quickly when food is plentiful
• Grow at the edges
• 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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Fungi can reproduce sexually and
asexually
Sexual reproduction involves the
fusion of two haploid hyphae of
compatible mating types
• 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
• Gamete nuclei divide at each
cell division producing dikaryotic
mycelium or heterokaryon
Sexual
reproduction
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– Functionally diploid
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Spores are the most common means of
reproduction among fungi
-May form from sexual or asexual processes
-Most are dispersed by wind
-Some by insects or small animals
Chytrids are the only group to retain ancestral
flagella and have motile zoospores
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Asexual reproduction
• Many fungi reproduce
both sexually and
asexually
• Some reproduce primarily
or exclusively asexually
• Most reproduce asexually
by generating chains of
spores at the hyphae tips
• Many use conidia
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• Many fungi produce substances in the fruiting
body to deter consumption
– Toxins can cause liver failure requiring a transplant
– Hallucinogenic or psychoactive substances
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General Biology of the Fungi
Fungi obtain food by secreting digestive enzymes into their
substrates
-They then absorb the organic molecules produced by this
external digestion
Fungi can break down cellulose and lignin
Some fungi are carnivorous
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Phylogenetic Relationships
There are five major fungal phyla
-Based on mode of sexual reproduction
- Increasing molecular sequence data suggest that fungi are
more closely related to animals than to plants
- The Glomeromycota, Ascomycota and Basidiomycota are
monophyletic
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-Other two phyla are not
Chytridiomycota
• Simplest fungi
• Earliest fungal phylum
• Some are single,
spherical cells that may
produce hyphae
• Others are branched,
aseptate hyphae
• Only fungi to produce
flagellate cells – for spore
or gamete dispersal
• Live in water or moist soil
• Most decomposers, some
parasites
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Zygomycota
•
•
•
•
Mycelium mostly aseptate hyphae
Produces asexual spores in sporangia
Named for zygospore produced sexually
Zygospore undergoes meiosis to produce
haploid spores
• Most are saprobes in soil
• Some are parasites
• Not monophyletic
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Glomeromycota
• Arbuscular mycorrhizal
(AM) fungi
• Only recently defined as
a group
• Aseptate hyphae
• Only asexual
reproduction using
unusually large
multinucleate spores
• Ability of early plants to
live on land may have
depended on help from
fungal associations
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Ascomycota
• Unique sporangia called asci
• Produce sexual spores called
ascospores
• Asci produced on fruiting
bodies called ascocarps
• Occur in terrestrial and
aquatic habitats
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Ascomycetes
Yeasts are unicellular ascomycetes
-Most reproduce asexually by budding
Yeasts can ferment
carbohydrates
-Break down glucose
into ethanol and CO2
-Used to make bread, beer and wine
-Saccharomyces cerevisiae
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• Many decomposers and parasites
–
–
–
–
Chestnut blight, Dutch elm disease, apple scab
Truffles, morels
Common lichen partner
Most yeasts including baking and brewing yeast and
Candida albicans
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Deuteromycetes
Include economically important molds
-Penicillium
-Penicillin
-Blue cheeses
-Aspergillus
-Soy sauce
-Soy paste
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Ecology of Fungi
Fungi, together with bacteria are the principal
decomposers in the biosphere
Fungi are virtually the only organisms capable
of breaking down cellulose and lignin
Fungi have entered into fascinating
symbioses with a variety of life forms
-Obligate symbiosis – Essential for fungus
survival
-Facultative symbiosis – Nonessential 25
Ecology of Fungi
Types of symbioses
-Pathogens and parasites benefit at the expense
of their host
-Commensals benefit one partner but do not harm
or benefit the other
-Mutualistic relationships benefit both partners
• Mycorhizzal fungi
Endophytes - fungi live in the intercellular spaces
inside plants; some protect their hosts from
herbivores by producing toxins
• Lichens
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Partnerships of particular fungi
and certain photosynthetic green
algae or cyanobacteria, and
sometimes both
Lichens
25,000 lichen species, but these
did not all descend from a
common ancestor
At least five separate fungal
lineages
3 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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Mycorhizzal fungi
• 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
• 2 most common types are ectomycorrhizae and
endomycorrhizae
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• Ectomycorrhizae
– Coat root surface and grow between
cells of roots
* Endomycorrhizae
Grow into root cell walls and plasma membranes
Arbuscular mycorrhizae form highly branched structures with high
surface area
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Ecology of Fungi
Fungi also form mutual symbioses with animals
-Ruminant animals host fungi in their gut
-Leaf-cutter Attini ants have domesticated
fungi which they keep in underground garden
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Fungal endophytes
• Fungi live within the tissues of various types of
plants
• Endophytes obtain organic food molecules from
plants
• In turn contribute toxins or antibiotics that deter
foraging animals, insect pests, and microbial
pathogens
• Plants with endophytes often grow better than
plants of the same species without endophytic
fungi
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Fungal Parasites and Pathogens
Fungal species cause many diseases in plants
-Armillaria has damaged large regions of
coniferous forests
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Fungal Parasites and Pathogens
Fungi can also spoil food products that have
been harvested and stored
Some fungi secrete toxins that make foods
poisonous
-Fusarium – Vomitoxin
-Aspergillus flavus - Aflatoxin
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Fungal Parasites and Pathogens
Fungi also cause human and animal diseases
-Candida – Thrush; vaginal infections
-Pneumocystis jiroveci – Pneumonia
-Athlete’s foot and nail fungus
Fungal diseases are difficult to treat because
of the close phylogenetic relationship
between fungi and animals
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Fungal Parasites and Pathogens
Batrachochytrium dendrobatidis causes
chitridiomycosis
-Responsible
for the
worldwide
decline in
amphibian
populations
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Nosema ceranae
growing on a bee
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