Transcript Slide 1

The Kingdom Fungi
• These morels are a
type of fungus prized
by many people for
their distinctive flavor
• Unlike the violets,
fungi are not plants
and do not produce
their own food
The Kingdom Fungi
The Kingdom Fungi
• In spring, if you know where to look, you can find one of
the most prized of all foods—the common morel—
growing wild in woodlands throughout the United States
• Its ridged cap is often camouflaged by dead leaves that
collect in abandoned orchards or underneath old oaks or
tulip poplars
• Some morels grow alone, but others grow in groups
• They appear suddenly, often overnight, and live for
only a few days
• What are these mysterious organisms?
• How do they grow so quickly?
KINGDOM FUNGI
• Diverse group of over 65,000 species
• Most fungi are saprophytic or parasitic, and a few are
predatory
– Saprophyte:
• Is an organism that feeds on dead organic matter
– Recycling the nutrients
– Referred to as decomposers
» Without decomposers, nutrients would not be reused and life
could not continue on earth
– Parasite:
• Derives its nutrients from a living host organism at the host’s
expense
• Cause many plant and animal diseases
– Predatory:
• Captures prey for food
• Example: Pleurotus ostreatus capture roundworms
What Are Fungi?
• Like mushrooms and molds, morels are
fungi
• The way in which many fungi grow from
the ground once led scientists to classify
them as nonphotosynthetic plants
• But they aren't plants at all
• In fact, fungi are very different from
plants
What Are Fungi?
• Fungi are eukaryotic heterotrophs that have cell
walls
– The cell walls of fungi are made up of chitin, a complex
carbohydrate that is also found in the external skeletons of
insects
• Recall that heterotrophs depend on other organisms
for food
– Unlike animals, fungi do not ingest their food
• Instead, they digest food outside of their bodies and
then absorb it
• Many fungi feed by absorbing nutrients from
decaying matter in the soil
• Others live as parasites, absorbing nutrients from the
bodies of their hosts
FUNGAL EVOLUTION
• Precambrian fossils about 900 million years old
• Late Carboniferous period, fossils indicate that
all modern divisions of fungi had evolved
• Most are terrestrial
– Indicates adaptive radiation shortly after plants and
animals colonized the land
• Like all eukaryotes, arose from prokaryotes
– Arose from other heterotrophs
– Present theory is that they evolved from red algae
Structure and Function of Fungi
• Except for yeasts, all fungi are multicellular
• Multicellular fungi are composed of thin
filaments called hyphae (singular: hypha)
• Each hypha is only one cell thick
• In some fungi, cross walls divide the hyphae
into cells containing one or two nuclei
– In the cross walls, there are tiny openings through
which the cytoplasm and nuclei can move
• Other hyphae lack cross walls and contain
many nuclei
CHARACTERISTICS
•
Hypha: vegetative filament of the fungus
– Types:
• Septate:
– Filaments with internal cross walls (septum)
– Individual cells have nuclei
• Coenocytic:
– Filaments without internal cross walls (septum)
– Filament contains many nuclei that move through the cytoplasm
– Grows at the tip where new membrane material is added by the action of Golgi
bodies
– A mat of interwoven hyphae is called mycelium
– Cell wall composed of chitin (not cellulose)
• Complex polysaccharide also found in the exoskeleton of insects and other
invertebrates
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•
Store food as glycogen (like animals)
Reproduce asexually (spores)(fragmentation) and sexually (gametes)
– Heterokaryotic hypha: genetically different nuclei coexist within a hypha
– Homokaryotic hypha: genetically similar nuclei coexist within a hypha
STRUCTURE OF FUNGI
Structure of Two Types of Hyphae
• Fungi are eukaryotes that
have cell walls made of
chitin
• Most fungi are made up of
filaments called hyphae
• In some fungi, the hyphae
are divided by cross walls
• These cells may contain one
or two nuclei
• In other fungi, the hyphae
lack cross walls and contain
many nuclei
Structure of Two Types of Hyphae
HYPHAE TYPES
STRUCTURE OF FUNGI
Fungus Structure
• The bodies of multicellular fungi are
composed of many hyphae tangled
together into a thick mass called a
mycelium
• The mycelium (plural: mycelia) is well
suited to absorb food because it
permits a large surface area to come in
contact with the food source through
which it grows
Structure of a Multicellular Fungus
• The body of a
mushroom is part of a
mycelium formed from
many tangled hyphae
• The major portion of the
mycelium grows below
ground
• The visible portion of
the mycelium is the
reproductive structure,
or fruiting body, of the
mushroom
Structure of a Multicellular Fungus
Fungus Structure
• What you recognize as a mushroom is
actually the fruiting body of a fungus
• A fruiting body is a reproductive
structure growing from the mycelium in
the soil beneath it
• Clusters of mushrooms are often part
of the same mycelium, which means
that they are part of the same organism
Fairy Rings
• Some mycelia can live for many years
• As time goes by, soil nutrients near the
center of the mycelium become depleted
• As a result, new mushrooms sprout only at
the edges of the mycelium, producing a ring
• People once thought fairies dancing in circles
during warm nights produced these rings, so
they were called “fairy rings”
• Over many years, fairy rings can become
enormous—from 10 to 30 meters in diameter
Reproduction in Fungi
• Most fungi reproduce both asexually and sexually
• Asexual reproduction takes place when cells or
hyphae break off from a fungus and begin to grow
on their own
• Some fungi also produce spores, which can scatter
and grow into new organisms
– Recall that a spore is a reproductive cell that is capable of
growing into a new organism by mitosis alone
• In some fungi, spores are produced in structures
called sporangia (singular: sporangium)
• Sporangia are found at the tips of specialized hyphae
called sporangiophores
Reproduction in Fungi
• Sexual reproduction in fungi usually
involves two different mating types
• Because gametes of both mating types
are about the same size, they are not
called male and female
• Rather, one mating type is called “+”
(plus) and the other “−” (minus)
Reproduction in Fungi
• When hyphae of opposite mating types meet, they
start the process of sexual reproduction by fusing,
bringing plus and minus nuclei together in the same
cell
• After a period of growth and development, these nuclei
form a diploid zygote nucleus
• In most fungi, the diploid zygote then enters meiosis,
completing the sexual phase of its life cycle by
producing haploid spores
• Like the spores produced asexually, these spores are
also capable of growing, by repeated rounds of
mitosis, into new organisms
How Fungi Spread
• Fungal spores are found in almost every
environment
• This is why molds seem to spring up in any
location that has the right combination of
moisture and food
• Many fungi produce dry, almost weightless
spores
• These spores scatter easily in the wind
• On a clear day, a few liters of fresh air may
contain hundreds of spores from many species
of fungi
How Fungi Spread
• If these spores are to germinate, they
must land in a favorable environment
• There must be the proper combination of
temperature, moisture, and food so that
the spores can grow
• Even under the best of circumstances, the
probability that a spore will produce a
mature organism can be less than one in a
billion
How Fungi Spread
• Other fungi are specialized to lure animals,
which disperse fungal spores over long
distances
• Stinkhorns smell like rotting meat, which
attracts flies
• When they land on the stinkhorn, the flies ingest
the sticky, smelly fluid on the surface of the
fungus
• The spore-containing fluid will pass
unharmed out of the flies' digestive systems,
depositing spores over many kilometers
FUNGI CLASSIFICATION
• Four Divisions:
– Based primarily on the structure of hyphae or
on the type of reproduction
Classification of Fungi
• The kingdom Fungi has over 100,000 species
• Fungi are classified according to their
structure and method of reproduction
• The methods by which fungi reproduce are
unlike those of any other kingdom
• The four main groups of fungi are:
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Common molds (Zygomycota)
Sac fungi (Ascomycota)
Club fungi (Basidiomycota)
Imperfect fungi (Deuteromycota)
CLASSIFICATION OF FUNGI
The Common Molds
• The familiar molds that grow on meat,
cheese, and bread are members of the
phylum Zygomycota, also called
zygomycetes
• Zygomycetes have life cycles that include a
zygospore
• A zygospore is a resting spore that contains
zygotes formed during the sexual phase of
the mold's life cycle
• The hyphae of zygomycetes generally lack cross
walls, although the cells of their reproductive
structures do have cross walls
DIVISION ZYGOMYCOTA
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Approximately 600 species
Mostly terrestrial organisms
Commonly found in soil and dung
Coenocytic hyphae
Example: Rhizopus Stolonifer
– Bread mold
– Three different types of hyphae:
• Rhizoids:
– Anchoring hyphae that penetrate the bread
– Produce digestive enzymes, and absorb nutrients
• Stolons:
– Hyphae that grow across the surface of the bread
• Sporangiophores:
– Upright hyphae that produce sporangia at their tips which produce
spores
Structure and Function of Bread Mold
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Black bread mold, Rhizopus stolonifer, is a familiar zygomycete
Expose preservative-free bread to dust, and you can grow the mold
Keep the bread warm and moist in a covered jar, and in a few days dark
fuzz will appear
With a hand lens, you can see delicate hyphae on moldy bread
There are two different kinds of hyphae:
– The rootlike hyphae that penetrate the bread's surface are rhizoids
• Rhizoids anchor the fungus to the bread, release digestive
enzymes, and absorb digested organic material
– The stemlike hyphae that run along the surface of the bread are
stolons
• The hyphae that push up into the air are the sporangiophores,
which form sporangia at their tips
– A single sporangium may contain up to 40,000 spores
Life Cycle of Molds
• The life cycle of black bread mold is shown in the figure
• Its sexual phase begins when hyphae from different mating
types fuse to produce gamete-forming structures known as
gametangia ( singular: gametangium)
– Haploid (N) gametes produced in the gametangia fuse with
gametes of the opposite mating type to form diploid (2N)
zygotes
– These zygotes develop into thick-walled zygospores, which
may remain dormant for months
• When conditions become favorable, the zygospore germinates,
then undergoes meiosis, and new haploid spores are released
• The significance of this sexual process—zygote formation followed
by meiosis—is that it produces new combinations of genetic
information that may help the organism meet changing
environmental conditions
ZYGOMYCOTA
RHIZOPUS STOLONIFER
Life Cycle of a Black Bread Mold
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Zygomycetes have life cycles that
include a zygospore
During sexual reproduction in the
bread mold Rhizopus stolonifer,
hyphae from two different
mating types form gametangia
The gametangia fuse, and
zygotes form within zygospore
The zygospore develops a thick
wall and can remain dormant
for long periods
The zygospore eventually
germinates, and a sporangium
emerges
The sporangium reproduces
asexually by releasing haploid
spores produced by meiosis
Life Cycle of a Black Bread Mold
DIVISION ZYGOMYCOTA
ASEXUAL REPRODUCTION
• Hormonal action causes upright
sporangiophores to form
– Sporangia form at the tips of sporangiophores
producing spores (sporangiospores) that are
dispersed by the wind
SEXUAL AND ASEXUAL
REPRODUCTION
OF ZYGOMYCOTA
ZYGOMYCOTA
LIFE CYCLE
DIVISION ZYGOMYCOTA
SEXUAL REPRODUCTION
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Called Conjugation
Two filaments line up next to each other
Hyphae of two mating strains come close together
Each hyphae encloses haploid (1N) nuclei
Hormones cause short branches to form on each hypha and grow
outward until they touch
• Septa form near the tip of each branch
– Resulting cell is a gametangium (1N) that contains several nuclei
– Gametangia fuse; then nuclei fuse in pairs (2N)
• Each pair contains one nucleus from each mating strain (2N)
• Zygote contains many diploid (2N) nuclei
– Wall surrounding the zygote (2N) thickens forming a protective, temporary
structure called a zygospore (2N)
» Meiosis occurs when the zygospore germinates forming new hyphae (1N)
SEXUAL AND ASEXUAL
REPRODUCTION
OF ZYGOMYCOTA
ZYGOMYCOTA
LIFE CYCLE
ZYGOMYCOTA
SEXUAL REPRODUCTION
CONJUGATION
ZYGOTE
DIVISION ZYGOMYCOTA
ASEXUAL/SEXUAL REPRODUCTION
• Provide adaptive advantages
• Asexual Reproduction:
– During periods when the environment is favorable
– Rapid formation of spores ensures the quick spread
of the species
• Sexual Reproduction:
– In periods of environmental stress
– Ensures genetic recombination before the hyphae die
The Sac Fungi
• Sac fungi, also known as ascomycetes, belong to the
phylum Ascomycota
• The phylum Ascomycota is named for the ascus, a
reproductive structure that contains spores
• There are more than 30,000 species of ascomycetes,
making it the largest phylum of the kingdom Fungi
• Some ascomycetes, such as the cup fungi, are large
enough to be visible when they grow above the ground
• Others, such as yeasts, are microscopic
DIVISION ASCOMYCOTA
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Sac fungi
Approximately 30,000 species
Largest Division of Fungi
Live in a variety of habitats, including
freshwater and saltwater
• Morels, powdery mildews, yeast, and cup
fungi
ASCOMYCETE
EDIBLE MOREL
Life Cycle of Sac Fungi
• The life cycle of an
ascomycete usually
includes both asexual
and sexual
reproduction
• The life cycle of a cup
fungus is shown in
the figure at right
Life Cycle of an Ascomycete
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•
The life cycle of ascomycetes
includes both asexual and
sexual reproduction
During asexual reproduction,
spores called conidia are
formed at the tips of specialized
hyphae called conidiophores
During sexual reproduction,
hyphae of two mating types
fuse to form hyphae with two
haploid (monoploid) nuclei (N +
N)
The N + N hyphae then form a
fruiting body, which eventually
releases ascospores
Ascomycetes are named for the
ascus, the reproductive
structure that contains
ascospores
Life Cycle of an Ascomycete
Life Cycle of Sac Fungi
• In asexual reproduction, tiny spores called
conidia (singular: conidium) are formed
at the tips of specialized hyphae called
conidiophores
• These spores get their name from the
Greek word konis, which means “dust”
• If a conidium lands in a suitable
environment, it grows into a haploid
mycelium
Life Cycle of Sac Fungi
• Sexual reproduction occurs when the
haploid hyphae of two different mating types
(+ and −) grow close together
• The N + N hyphae then produce a fruiting
body in which sexual reproduction continues
• Gametangia from the two mating types fuse,
but the haploid (N) nuclei do not fuse
• Instead, this fusion produces hyphae that
contain haploid nuclei from each of the
mating types (N + N)
Life Cycle of Sac Fungi
• The ascus (plural: asci) forms within the fruiting
body
• Within the ascus, two nuclei of different
mating types fuse to form a diploid zygote
(2N)
– The zygote soon divides by meiosis, producing
four haploid cells
• In most ascomycetes, meiosis is followed by a
cycle of mitosis, so that eight cells known as
ascospores are produced
• In a favorable environment, an ascospore can
germinate and grow into a haploid mycelium
DIVISION ASCOMYCOTA
• Sexual Reproduction:
– Hyphae of the Ascogonium (female gametangium) fuses with the
Antheridium (male gametangium)
• Gametangia fuse, and male nuclei move into the ascogonium
• Male and female nuclei pair but do not fuse
• Cell divide forming heterokaryotic hyphae that intertwine forming an
ascocarp
– Reproductive body of an ascomycete
– Sacs called asci form on the surface
» Each ascus encloses two nuclei
» Nuclei fuse
» Diploid nucleus undergoes meiosis producing four haploid nuclei
followed by a mitotic division resulting in 8 haploid ascospores
» Ascus ruptures releasing ascospores into the air
» Ascospores germinate into new hyphae on the ground
ASCOMYCOTA
• Asexual Reproduction:
– Produces spores called conidium
• Conidia form on the ends of specialized branches
called conidiophores
ASCOMYCETE REPRODUCTION
ASCOMYCOTA LIFE CYCLE
Yeasts
• Yeasts are unicellular fungi
• The yeasts used by humans for baking
and brewing are classified as
ascomycetes because they form asci
with ascospores during the sexual
phase of their life cycle
Yeasts
• You might think of yeast as a lifeless, dry powder
that is used to make bread
• Actually, the dry granules contain ascospores, which
become active in a moist environment
• To see this for yourself, add a spoonful of dry yeast to
half a cup of warm water that contains some sugar
• In about 20 minutes, when you examine a drop of
this mixture under a microscope, you will be able to
see cell division in the rapidly growing yeast cells
• The process of asexual reproduction you are
observing is called budding
Yeasts
• The common yeasts used for baking and brewing are members
of the genus Saccharomyces, which means “sugar fungi”
• These yeasts are grown in a rich nutrient mixture containing
very little oxygen
• Prior to baking, the nutrient mixture is a mound of thick dough
• Lacking oxygen, the yeasts within the mixture use the process
of alcoholic fermentation to obtain energy
– The byproducts of alcoholic fermentation are carbon dioxide and
alcohol
• The carbon dioxide gas makes beverages bubble and bread
rise (by producing bubbles within the dough)
• The alcohol in bread dough evaporates during baking
• In brewing, alcohol remains in the resulting alcoholic
beverages
DIVISION ASCOMYCOTA
– Yeast: unicellular
• Asexual Reproduction: budding
• Sexual Reproduction: formation of a zygote by the
fusion of two ascospores
• 600 species
– Saccharomyces cerevisiae used in brewing processes
• Ability to breakdown carbohydrates forming ethyl
alcohol and carbon dioxide gas makes yeast useful
in industry
– Baking and brewing
The Club Fungi
• The phylum Basidiomycota, or club
fungi, gets its name from a specialized
reproductive structure that resembles a
club
• The spore-bearing structure is called the
basidium (plural: basidia)
• Basidia are found on the gills that grow on
the underside of mushroom caps
DIVISION BASIDIOMYCOTA
• Approximately 25,000 species
• Called club fungi
• Examples: mushrooms, toadstools,
puffballs, rusts, and smuts
DIVISION BASIDIOMYCOTA
• Basidiocarp: mushroom
– Reproductive body of a basidiomycete
– Formed when underground hyphae grow upward and intertwine
– Cap (fruiting body) is attached to a stalk (stem)
• Underside are radiating rows of gills which contain specialized club-shaped
reproductive cells called basidia
– In each basidium two nuclei become isolated by a complete septum
– Nuclei fuse and form a diploid zygote
– Meiosis then results in four nuclei that are pushed into cytoplasmic extensions to
form basidiospores
– At maturity, the basidiospores are released and germinate into new homokaryotic
hyphae
– As the homokaryotic hyphae grow, septa form so that each cell contains one
nucleus
» These homokaryotic, septate hyphae are called the primary mycelium
– Primary hyphae grow and fuse with hyphae from another mating strain resulting in
the formation of secondary hyphae
» Hyphae of these mycelium are heterokaryotic, containing one nucleus from
each mating strain in each cell
– Secondary mycelium intertwines and forms a basiocarp
Life Cycle of Club Fungi
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Basidiomycetes undergo what is
probably the most elaborate life cycle
of all the fungi
As shown in the figure at right, a
basidiospore germinates to produce
a haploid primary mycelium, which
begins to grow
Before long, the mycelia of different
mating types fuse to produce a
secondary mycelium
The cells of the secondary mycelium
contain haploid nuclei of each
mating type
Secondary mycelia may grow in the
soil for years, reaching an enormous
size
A few mycelia have been found to
be hundreds of meters across,
making them perhaps the largest
organisms in the world
Life Cycle of a Basidiomycete
• The club fungi are named
after the club shape of their
reproductive structure, the
basidium
• The cap of a basidiomycete
such as a mushroom is
composed of tightly packed
hyphae
• The lower side of the cap is
composed of gills—thin
blades of tissue lined with
basidia that produces
basidiospores
Life Cycle of a Basidiomycete
BASIDIOMYCETE
REPRODUCTION
BASIDIOMYCETE
REPRODUCTION
BASIDIOMYCOTA
LIFE CYCLE
FRUITING BODY
BASIDIOCARP
FRUITING BODY
BASIDIOCARP
FRUITING BODY
BASIDIOCARP
FRUITING BODY
BASIDIOCARP
FRUITING BODY
BASIDIOCARP
PUFFBALL OF
BASIDIOMYCETES
Life Cycle of Club Fungi
• When the right combination of moisture
and nutrients occurs, spore-producing
fruiting bodies push above the ground
• You would recognize these fruiting
bodies as mushrooms
• Each mushroom begins as a mass of
growing hyphae that forms a button, or
thick bulge, at the soil's surface
Life Cycle of Club Fungi
• Fruiting bodies expand with astonishing
speed, sometimes producing fully
developed mushrooms overnight
• This remarkable growth rate is caused
by cell enlargement, not cell division
• The cells of the hyphae enlarge by
rapidly taking in water
Life Cycle of Club Fungi
• When the mushroom cap opens, it exposes
hundreds of tiny gills on its underside
• Each gill is lined with basidia
• The two nuclei in each basidium fuse to form a
diploid (2N) zygote cell, which then undergoes
meiosis, forming clusters of haploid basidiospores
– The basidiospores form at the edge of each basidium and,
within a few hours, are ready to be scattered
• Mushrooms are truly amazing reproductive
structures—a single mushroom can produce billions
of spores, and giant puffballs can produce trillions
Diversity of Club Fungi
• In addition to mushrooms, basidiomycetes
include shelf fungi, which grow near the
surfaces of dead or decaying trees
• The visible bracketlike structure that forms
is a reproductive structure, and it, too, is a
prolific producer of spores
• Puffballs, earthstars, jelly fungi, and
plant parasites known as rusts are
other examples of basidiomycetes
Edible and Inedible Mushrooms
• Many types of fungi have long been considered
delicacies, and several different species of
mushrooms are cultivated for food
• You may have already tasted sliced
mushrooms on pizza, feasted on delicious
sautéed portobello mushrooms, or eaten
shiitake mushrooms
• When properly cooked and prepared, domestic
mushrooms are tasty and nutritious
FUNGI IN INDUSTRY
Edible and Inedible Mushrooms
• Wild mushrooms are a different story:
Although some are edible, many are
poisonous
• Because many species of poisonous
mushrooms look almost identical to edible
mushrooms, you should never pick or eat
any mushrooms found in the wild
• Instead, mushroom gathering should be left
to experts who can positively identify each
mushroom they collect
• The result of eating a poisonous mushroom can
be severe illness, or even death
The Imperfect Fungi
• Fungi are usually classified by the sexual phase of their life
cycle
– So, what do biologists do when they discover a fungus that does
not seem to have a sexual phase?
– Until a sexual phase is discovered, scientists place it in the
phylum called Deuteromycota, or the imperfect fungi
• The term imperfect, by the way, doesn’t mean that there’s
anything wrong with these organisms
– It simply means that our understanding of their life cycles
may not be perfect
• The Deuteromycota are fungi that cannot be placed in other
phyla because researchers have never been able to observe a
sexual phase in their life cycles
• A majority of the imperfect fungi closely resemble ascomycetes
• Others are similar to basidiomycetes, and a few resemble the
zygomycetes
The Imperfect Fungi
• One of the best-known genera of the
imperfect fungi is Penicillium
• The species Penicillium notatum is a mold that
frequently grows on fruit and is the source of
the antibiotic penicillin
• Like the ascomycetes, Penicillium reproduces
asexually by means of conidia, leading many
biologists to conclude that Penicillium
evolved from an ascomycete that lost the
sexual phase of its life cycle
DIVISION DEUTEROMYCOTA
• Sometimes called the imperfect fungi or, Fungi
Imperfecti
• 10,000 species
• Classification based on type of asexual
reproduction
• No sexual reproductive phase discovered
– Placed in this Division until a sexual phase, if it exist,
is identified
• Some forms cause ringworm and athlete’s foot
• Aspergillus used to ferment soy beans in the
production of soy sauce
Ecology of Fungi
• Fungi have been around since life first moved onto land
• In fact, the oldest known fossils of fungi were formed
about 460 million years ago
• At that time, the largest land plants were small
organisms similar to mosses
• Paleontologists think that fungi helped early plants
to obtain nutrients from the ground
• Their early appearance suggests that fungi may have
been essential to plants' successful colonization of
the land, one of the key events in the history of life
Ecology of Fungi
• Over time, fungi have become an
important part of virtually all
ecosystems, adapting to conditions in
every corner of Earth
• Because most fungi live their lives out of
our sight, people often overlook them
• But without fungi, the world would be a
very different place
All Fungi Are Heterotrophs
• As heterotrophs, fungi cannot manufacture their own
food
• Instead, they must rely on other organisms for their
energy
• Unlike animals, fungi cannot move to capture food,
but their mycelia can grow very rapidly into the
tissues and cells of plants and other organisms
• Many fungi are saprobes, organisms that obtain food
from decaying organic matter
• Others are parasites, which harm other organisms
while living directly on or within them
• Still other fungi are symbionts that live in close and
mutually beneficial association with other species
All Fungi Are Heterotrophs
• Although most fungi feed on decaying
matter, a few feed by capturing live animals
• Pleurotus ostreatus is a carnivorous fungus
that lives on the sides of trees
• As roundworms crawl into the fungus to
feed, they are exposed to a fungal chemical
that makes them become sluggish
• As the worms slow to a stop, fungal hyphae
penetrate their bodies, trapping them in
place and then digesting them
Fungi as Decomposers
• Fungi play an essential role in maintaining
equilibrium in nearly every ecosystem, where they
recycle nutrients by breaking down the bodies and
wastes of other organisms
• Many fungi feed by releasing digestive enzymes that
break down leaves, fruit, and other organic material
into simple molecules
• These molecules then diffuse into the fungus
• The mycelia of fungi produce digestive enzymes that
speed the breakdown of wastes and dead organisms
• In so doing, they promote the recycling of nutrients
and essential chemicals, helping to maintain
ecosystem equilibrium
Fungi as Decomposers
• Imagine a world without decomposers
• Without decay, the energy-rich compounds
that organisms accumulate during their
lifetimes would be lost forever
• Many organisms, especially plants, remove
important trace elements and nutrients from the
soil
• If these materials were not returned, the soil
would quickly be depleted, and Earth would
become lifeless and barren
Fungi as Parasites
• As useful as many fungi are, others can
infect both animals and plants, disrupting
their internal equilibrium and causing
disease
• Parasitic fungi cause serious plant and
animal diseases
• A few cause diseases in humans
Plant Diseases
• Fungi cause diseases such as corn smut, which
destroys corn kernels
• Mildews, which infect a wide variety of fruits, are also
fungi
• Fungal diseases are responsible for the loss of
approximately 15 percent of the crops grown in
temperate regions of the world
• In tropical areas, where high humidity favors fungal
growth, the loss of crops is sometimes as high as 50
percent
• Fungi are in direct competition with humans for food
• Unfortunately for us, sometimes fungi win that
competition
Plant Diseases
• One fungal disease—wheat rust—affects one of the
most important crops grown in North America
• Rusts are caused by a type of basidiomycete that needs
two different plants to complete its life cycle
• Spores produced by rust in barberry plants are carried
by the wind into wheat fields
• There, the spores germinate and infect wheat plants
• The patches of rust produce a second type of spore that
infects other wheat plants, allowing the disease to
spread through the field like wildfire
Plant Diseases
• Later in the growing season, a new variety of spore is
produced by the rust
• These tough black spores easily survive through the
winter
• In spring, they go through a sexual phase and produce
spores that infect barberry plants
• Once on the barberry leaves, the rust produces the
spores that infect wheat plants, and the cycle
continues
• Fortunately, once agricultural scientists understood
the life cycle of the rust, they were able to slow its
spread by destroying barberry plants
Human Diseases
• Fungal parasites can also infect humans
• One deuteromycete can infect the areas
between the toes, causing the infection
known as athlete's foot
• The fungus forms a mycelium directly within
the outer layers of the skin
– This produces a red, inflamed sore from which the
spores can easily spread from person to person
• When the same fungus infects other areas,
such as the skin of the scalp, it produces a
red scaling sore known as ringworm, which
is not a worm at all
FUNGAL DISEASES
Human Diseases
• The microorganism Candida albicans, a yeast, can
disrupt the equilibrium within the human body, causing
fungal disease
• Candida, which grows in moist regions of the body, is
usually kept in check by competition from bacteria
that grow in the body and by the body's immune
system
• This normal balance can be upset by many factors,
including the use of antibiotics, which kill bacteria,
or by damage to the immune system
• When this happens, Candida may produce thrush, a
painful mouth infection
• Yeast infections of the female reproductive tract
usually are due to overgrowth of Candida
FUNGAL DISEASES
Other Animal Diseases
• As problematic as human fungal diseases can be, few fungal
diseases are as deadly as the infection by one fungus from the
genus Cordyceps
• This fungus infects grasshoppers in rain forests in Costa Rica
• Microscopic spores become lodged in the grasshopper, where they
germinate and produce enzymes that slowly penetrate the insect's
tough external skeleton
• The spores multiply in the insect's body, digesting all its cells and
tissues until the insect dies
• To complete the process of digestion, hyphae develop,
cloaking the decaying exoskeleton in a web of fungal material
• Reproductive structures, which will produce more spores that
will spread the infection, then emerge from the grasshopper's
remains, as shown in the photograph
Grasshopper Infected by a
Fungus
• This grasshopper is the
victim of Cordyceps, a
fungus
• Once the fungus's tiny
spore enters the
insect's body, it
multiplies rapidly and
digests body tissues
• The structures growing
out of the
grasshopper's body are
the fungus's fruiting
bodies
Grasshopper Infected by a
Fungus
Symbiotic Relationships
• Fungi often grow in close association with
members of other species in symbiotic
relationships
• Although fungi are parasites in many of these
relationships, that is not always the case
• Some fungi form symbiotic relationships in
which both partners benefit
• Two such mutualistic associations, lichens
and mycorrhizae, are essential to many
ecosystems
Lichens
• Lichens are not single organisms
• Rather, they are symbiotic associations
between a fungus and a photosynthetic
organism
• The fungi in lichens are usually
ascomycetes, although a few are
basidiomycetes
• The photosynthetic organism is either a
green alga or a cyanobacterium, or both
• The figure below shows the structure of a lichen
Structure of a Lichen
• Lichens are a mutualistic
relationship between a
fungus and an alga or a
cyanobacterium, or both
• The protective upper surface
of a lichen is composed of
fungal hyphae
• Below this is the layer of
cyanobacteria or algae with
loosely woven hyphae
• The third layer consists of
loosely packed hyphae
• The bottom layer is a
protective surface covered
by small projections that
attach the lichen to a rock or
tree
Structure of a Lichen
Lichens
• Lichens are extremely resistant to drought and cold
• Therefore, they can grow in places where few other
organisms can survive—on dry, bare rock in deserts and
on the tops of mountains
• Lichens are able to survive in these harsh environments
because of the relationship between the two partner
organisms
• The algae or cyanobacteria carry out
photosynthesis, providing the fungus with a source
of energy
• The fungus, in turn, provides the algae or bacteria
with water and minerals that it collects and protects
the delicate green cells from intense sunlight
Lichens
• Lichens are often the first organisms to enter
barren environments, gradually breaking
down the rocks on which they grow
• In this way, lichens help in the early stages of
soil formation
• Lichens are also remarkably sensitive to air
pollution, and they are among the first
organisms to be affected when air quality
deteriorates
SYMBIOTIC RELATIONSHIP
TOP: MYCORRHIZAE
BOTTOM: FOLIOSE LICHEN
MUTUALISM
• Type of symbiosis in which both organisms
benefit
MYCORRHIZAE
• Symbiotic association between fungi and plant roots
• Occurs in about 80% of plants
• Helps plants absorb water and nutrients, such as
phosphorus and potassium, by forming extensive
networks of fungal hyphae in the soil increasing the
surface area in the soil for absorption
• Digestive action of the fungal enzymes provides
nutrients that can be readily absorbed by the plant
• Fungi absorbs some of the sugars created by the plant
during photosynthesis
Mycorrhizae
• Fungi also form mutualistic relationships
with plants
• Almost half of the tissues of trees are hidden
beneath the ground in masses of tangled roots
• These roots are woven into a partnership with
an even larger web of fungal mycelia
• These associations of plant roots and fungi are
mycorrhizae (singular: mycorrhiza)
Mycorrhizae
• Scientists have known about this
partnership for years, but recent research
shows that it is more common and more
important than was previously thought
• Researchers now estimate that 80
percent of all plant species form
mycorrhizae with fungi
Mycorrhizae
• How do plants and fungi benefit from each other?
• The tiny hyphae of the fungi aid plants in absorbing
water and minerals
• They do this by producing a network that covers the
roots of the plants and increases the effective surface
area of the root system
• This allows the roots to absorb more water and
minerals from the soil
• In addition, the fungi release enzymes that free
nutrients in the soil
• The plants, in turn, provide the fungi with the
products of photosynthesis
Mycorrhizae
• The presence of mycorrhizae is essential for
the growth of many plants
• The seeds of some plants, such as orchids,
cannot germinate in the absence of
mycorrhizal fungi
• Many trees are unable to survive without fungal
symbionts
• Mycorrhizal associations have even been cited
as an adaptation that was critical in the evolution
of land plants from more-aquatic ancestors
Mycorrhizae
• Mycorrhizal relationships are often very
specialized
• For example, the Douglas fir forests of the
Pacific Northwest are dependent on the
presence of a particular species of white truffle
• In Europe, black truffles are found growing with
oak and beech trees
• The fly agaric grows mostly with birch and pine
trees
Mycorrhizae
• Why is this networking relationship so
important?
• The partnership between plant and fungus does
not end with a single plant
• The roots of each plant are plugged into
mycorrhizal networks that connect many
plants
• What's more astounding is that these networks
appear to connect plants of different species
Mycorrhizae
• A recent experiment showed that carbon atoms
from one tree often end up in another nearby
tree
• In an experiment using carbon isotopes to
track the movement of carbon, ecologist
Suzanne Simard found that mycorrhizal fungi
transferred carbon from paper birch trees
growing in the sun to Douglas fir trees
growing in the shade
• As a result, the sun-starved fir trees thrived,
basically by being “fed” carbon from the
birches
Mycorrhizae
• Simard's findings suggest that plants are
far from being isolated individuals, as was
previously thought
• Instead, plants—and their associated
fungi—may be evolving as part of an
ecological partnership