Transcript Lecture #4

Lecture #4
Fungi
“The Mighty Mushroom”
• take a walk through a forest
• mushrooms are truly are the largest
organisms in the forest
• Kingdom Fungi:
– not just mushrooms!
– approximately 100,000 species now
described
– may be as many as 1.5 million species
– range from unicellular to complex
multicellular organisms
– just about every terrestrial and aquatic
environment
– essential decomposers in ecosystems
• critical for the release of nutrients into the
ecosystem
– included with animals and choanoflagellates
in clade Opisthokonta
• diverged about a billion years ago
Nutrition
• like animals, fungi are heterotrophs
– cannot make their own food like algae and plants
• unlike animals – they do not ingest their food
• fungi absorb nutrients from its environment
• many fungi secrete powerful hydrolytic enzymes
that breakdown complex organic compounds into
smaller ones that can be absorbed
• others use enzymes to penetrate the walls of cells
– absorption
• digestion of both living and dead sources
Body
Structure
• most common body structures are:
– 1. multicellular filaments
– 2. yeasts
• relatively few species grow as yeasts
– those that do inhabit moist environments
Cell wall
• most grow as multicellular filaments
• body structure:
– enhances their ability to absorb nutrients
– formation of a network of tiny filaments called
hyphae
– hyphae form an interwoven mass called a mycelium
– a mycelium infiltrates the material on which it feeds
Cell wall
Nuclei
Pore
Septum
Septate hypha
Nuclei
Coenocytic hypha
Reproductive structure
• 1cm3 of soil may have as much as 1 km of hyphae in a
Hyphae
mycelium
– mycelia grow very fast – nutrients for growth are
carried rapidly via cytoplasmic streaming to the
growing hyphae
• grow from the tip
• “spitzenkorper” – membrane system of vesicles from
the golgi that travel to the growing tip via the
cytokeleton and exocytose their contents for the
growth of the hyphal cell wall
– the emphasis is on increasing mycelium length NOT
width
Spore-producing
structures
20 µm
Mycelium
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singular = hypha
consist of tubular cell wall surrounding a plasma
membrane and cytoplasm of the cell
cell wall is strengthened by chitin (not cellulose =
plants)
Fungal
Hyphae
– nitrogen containing polysaccharide
– strong yet flexible
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hyphae is divided into individual cells by walls
called septa
Cell wall
– septa have relatively large pores
– allow the passage of ribosomes, mitochondria and
nuclei between cells
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those that lack septa are called ceonocytic fungi
mycorrhizal fungi: fungi with mutually beneficial
relationships between the fungus and plant roots
– mycorrhiza = symbiotic relationship between a fungus
and the root of a vascular plant
– the hyphae are specialized = haustoria
– these fungi improve the delivery of nutrients to the
plant’s root – e.g. phosphate and nitrogen ions
– plants supply the fungus with the organic materials it
needs to survive
– ectomycorrhizal fungi= sheaths of hyphae over the
root
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grow into the extracellular spaces of the root’s cortex
– arbuscular mycorrhizal fungi = extend branching
hyphae through the root cell wall via tubes
– these haustoria remain separated from the plant by
the plant’s plasma membrane!
Cell wall
Nuclei
Pore
Septum
Nuclei
Septate hypha
Coenocytic hypha
Plant
cell
wall
Fungal hypha
Plant cell
Haustoria
Haustorium
Plant cell
plasma
membrane
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reproduction through the production of spores
spores are carried by wind or water
germination upon exposure to moisture to produce a new mycelium
sexual reproduction: consists of three stages – plasmogamy, karyogamy and meiosis
Reproduction
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begins when hyphae from two mycelia release pheromones
bind to receptors on the opposite mating type – hyphae extends toward the source of the pheromones (i.e.
towards each other)
the hyphae meet and fuse – hyphae of the same mating type cannot fuse
two cytoplasms fuse = plasmogamy
nuclei from these two “parental” fungi do not fuse right away – fungus is now called a heterokaryon (”different
nuclei”)
• some species – exchange of chromosomes and even crossing over – genetic variability
hours or decades later (!) the nuclei will fuse = karyogamy
sexual reproduction:
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karyogamy: life cycle stage of fusion
of two haploid nuclei in fungi
production of a diploid zygote
meiosis follows – regenerating
haploid spores
karyogamy and meiosis generate
genetic variability
spores are dispersed to germinate
and form a new mycelium
Key
Heterokaryotic
stage
Haploid (n)
Heterokaryotic
(unfused nuclei from
different parents)
Diploid (2n)
PLASMOGAMY
(fusion of cytoplasm)
KARYOGAMY
(fusion of nuclei)
Spore-producing
structures
Zygote
Spores
ASEXUAL
REPRODUCTION
Mycelium
SEXUAL
REPRODUCTION
MEIOSIS
GERMINATION
GERMINATION
Spores
Spore-producing
structures
• asexual reproduction: most fungi can reproduce sexually and asexually
depending on nutrient availability
– 20,000 species use only asexual reproduction
– reproduce by growing as filamentous fungi that produce haploid spores
– these species are informally known as molds if they form visible mycelia
– other reproduce asexually by growing as single-celled yeasts
– don’t produce spores – reproduction is by cell division or by budding off of the parental cell
10 m
Key
Heterokaryotic
stage
Haploid (n)
Heterokaryotic
(unfused nuclei from
different parents)
Diploid (2n)
Parent
cell
KARYOGAMY
(fusion of nuclei)
Spore-producing
structures
Zygote
Spores
ASEXUAL
REPRODUCTION
Bud
PLASMOGAMY
(fusion of cytoplasm)
Mycelium
SEXUAL
REPRODUCTION
MEIOSIS
GERMINATION
GERMINATION
Spores
Spore-producing
structures
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1. Chytridiomycota
2. Zygomycota
3. Glomeromycota
4. Ascomycota
5. Basidiomycota
Club
fungi
Basidiomycota
• then moved to land – fossils of
the earliest vascular land plants
have fungal associations
(mycorrhizea)
• radiated into 5 Phyla
Sac
fungi
Ascomycota
– some still have flagella – called
chytrids
Arbuscular
mycorrhizal
fungi
Glomeromycota
Chytrids
Zygote
fungi
Zygomycota
Fungal Diversity
Chytridiomycota
• descended from a unicelluar,
aquatic flagellated protist
• earliest lineages of fungus
thought to possess flagella
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1. Phylum:
Chytridiomycota
known as the chytrids
most primitive of the fungi
ubiquitous in lakes and soil
some species are decomposer (saprobes)
others are parasitic (protists, plants and animals)
diverged the earliest in fungal evolution
like other fungi - walls are made of chitin
– also share many enzymes and metabolic pathways with other fungal groups
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unique in that they have flagellated spores called zoospores
some exist as single cells, others form colonies with hyphae
do not have a true mycelium – fungal body is called a thallus
closely related to the zygomycete group of fungus
are considered a coenocytic fungus – no septal walls in their hyphae
extensions off the hyphae produce digestive enzymes for decomposition of their
substrate
Hyphae
1. Chytridomycota
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asexual reproduction: production of diploid
zoospores by mitosis
– zoospores produced from a zoosporangium by
mitosis
– zoosporangium located at the tip of hyphae
– swim to new areas and undergo mitotic growth
– to form a new thallus (i.e. mycelium)
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Sexual
sexual reproduction: production of haploid
zoospores by meiosis
– zoosporangium that produce haploid zoospores
by meiosis are called gametangia
• gametangium – reproductive structure
that produces and releases gametes
– zoospores are of opposite mating type – “male”
and “female”
– female zoospore attracts the male
– two gametes fuse into a zygote
• motile and biflagellated
– zygote forms a protective wall to become a
dormant cyst
– with favorable conditions – redevelops into a
haploid thallus/mycelium
Asexual
2. Phylum: Zygomycota
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1,100 known species
diverse in lifestyles
fast-growing molds
other can be parasites
others can be commensal (neutral) symbiont forms with animals
e.g. Rhizopus stolonifer – black bread mold
– typical of a zygomycete
– mycelium forms as a spread of horizontal hyphae over the food –
penetrates it and absorb the nutrients
– hyphae are coenocytic – septa are found only where the reproduction cells
are formed
– spore dispersal through the air eventually passes it onto other substrates
for continued growth
– sexual reproduction: “parents” are mycelia with two mating types: “-” and “+”
• two mating types of hyphae form extensions toward one another (pheromones)
• 2 gametangia form between them – multiple haploid nuclei within each
• undergo plasmogamy (cytoplasm fusion, no nuclear fusion yet) to produce a
zygosporangium
– said to be heterokaryotic – no nuclear fusion yet!!
• zygosporangium thickens – remains resistant and dormant for months
• favorable conditions – karyogamy occurs = diploid nuclei
• followed by meiosis into haploid spores
– from the cyst arises a sporangium (called a fruiting body) for the production of haploid spores
– this is what we see as the black fuzziness on bread
Key
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Haploid (n)
Heterokaryotic (n + n)
http://academic.kellogg.ed
u/herbrandsonc/bio111/ani
mations/0120.swf
Diploid (2n)
PLASMOGAMY
Rhizopus
growing
on bread
Mating
type (+)
Gametangia with
Mating haploid nuclei
type (–)
100 µm
Young
zygosporangium
(heterokaryotic)
SEXUAL
REPRODUCTION
Dispersal and
germination
Sporangia
Sporangium
ASEXUAL
REPRODUCTION
MEIOSIS
Dispersal and
germination
50 µm
Mycelium
KARYOGAMY
Diploid
nuclei
Zygosporangium
(heterokaryotic)
– asexual reproduction: spores develop within the sporangium/fruiting body
and are dispersed through the air
• if they land on moist food – germinate and grow into new mycelia which
can continue to reproduce new sporangia and reproduce asexually
• in poor conditions, these germinating mycelia will grow and undergo
sexual reproduction
• some species can aim their sporangium at the site of food (Pilobolus)
Key
Haploid (n)
Heterokaryotic (n + n)
Diploid (2n)
PLASMOGAMY
Rhizopus
growing
on bread
Mating
type (+)
Gametangia with
Mating haploid nuclei
type (–)
100 µm
Young
zygosporangium
(heterokaryotic)
SEXUAL
REPRODUCTION
Dispersal and
germination
Sporangia
Sporangium
ASEXUAL
REPRODUCTION
MEIOSIS
Dispersal and
germination
50 µm
Mycelium
KARYOGAMY
Diploid
nuclei
Zygosporangium
(heterokaryotic)
• Pilobolus: zygomycete that lives in the dung of grass eating mammals
– sends up a delicate tube topped with a water-filled clear vesicle and a black disc
called the mitosporangium or sporangium
– must disperse its spores away from the cow dung because the spore must be eaten
by the cow and passed through its digestive system to continue its life cycle
– does so through an explosive dispersal mechanism
– the sporangium is exploded from the underlying vesicle
– increases in osmotic pressure within the vesicle explodes it outward and
disintegrates the sporangium on top – acts as a water cannon
– this structure is also photosensitive – there is a light-sensing retina like disc within
the vesicle which can track the light
3. Phylum Ascomycota
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cup fungus
60,000 species
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red, blue and green molds
also includes mildews
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defined by the formation of a
cup-like ascocarp
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The cup-shaped ascocarps (fruiting
bodies) of Aleuria aurantia give this
species its common name: orange
peel fungus.
a sac-like reproductive structure
containing asci that produce haploid
spores following sexual union
edible portion of this fungus
e.g. morels and truffles
many found on decaying
vegetation
also include the tree fungi
half the species associate with
algae to form lichens
most are septate within their
hyphae
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).
3. Phylum
Ascomycota
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mildews: general term of mildew
means dicolorations and odors
created by fungus
mildews are actually are parasitic
fungi of plants
white powdery appearance
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Claviceps purpurea parasitizes rye
and other grasses causing the
disease ergotism
ergotism can result from eating
infected grains and results in
gangrene, psychotic delusions,
nervous spasms, abortion and
convulsions
known as St. Anthony’s fire
pharmacologic activities of ergot
are due to lysergic acid
diethylamide (LSD)
• asexual reproduction: fungus produces a powdery structures called
conidiophores
– mitosis within these structure produces spores called conidia
– conidia are produced at the tips of the conidiophores (zygomycotes – spores
formed within a sporangia)
– conidia carried by air currents to new locations
– germination leads to specialized hyphae formation called haustoriae – penetrate
the epidermis of leaves and absorb nutrients
– eventual production of a new mycelium
Key
Haploid (n)
Dikaryotic (n + n)
Diploid (2n)
Conidia;
mating type (–)
Dispersal
Germination
ASEXUAL
Mycelium
REPRODUCTION
Mating
type (+)
Ascus
(dikaryotic)
Dikaryotic hyphae
extended from
ascogonium
Mycelia
Conidiophore
Germination
Dispersal
Asci
Eight
ascospores
SEXUAL
KARYOGAMY
REPRODUCTION
Diploid nucleus
(zygote)
Four
haploid
nuclei
Ascocarp
PLASMOGAMY
MEIOSIS
•
sexual reproduction: conidia also involved in sexual reproduction
– fusion of the hyphae from opposite mycelia mating types is followed by plasmogamy
– results in a the formation of reproductive structures called ascogonia (singular =
ascogonium)
– from these ascogonia arise multiple dikaryotic hyphae
– each hypha produces a dikaryotic ascus (plural = asci) at its tip
• dikaryotic = 2 nuclei in each ascus
– within each individual ascus – karyogamy unites the 2 nuclei and meiosis follows to form
4 haploid nuclei
– these nuclei divide ONCE to form a total of 8 ascospores each with a single nuclei
– multiple asci become surrounded by a protective ascocarp (aggregation of hyphae)
– ascospores are ejected from this ascocarp
Key
Haploid (n)
Dikaryotic (n + n)
Diploid (2n)
Conidia;
mating type (–)
the long dikaryotic stage in
these fungi allows for
extensive genetic recombination
Dispersal
Germination
ASEXUAL
REPRODUCTION Mycelium
Mating
type (+)
PLASMOGAMY
Ascus
(dikaryotic)
Dikaryotic hyphae
extended from
ascogonium
Mycelia
Conidiophore
SEXUAL
REPRODUCTION
Germination
Dispersal
Asci Eight
ascospores
Ascocarp
Diploid nucleus
(zygote)
Four
haploid
nuclei
Ascocarp
KARYOGAMY
MEIOSIS
4. Phylum:
Basidiomycota
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club fungus
30,000 species
includes the mushrooms, shelf fungi,
molds and mycorrizhae, rusts and
smuts
important decomposers of wood
saprophoric and parasitic species
(rusts and smuts)
all are characterized by the formation
of a basidium – club-shaped structure
which is diploid and produces
basidiospores
fruiting bodies are also called
basidiocarps andare the structures we
call mushrooms, puffballs, toadstools,
bracket fungus
toadstools = poisonous mushrooms
beneath the fruiting body are
extensive mats of mycelia that feed on
decaying vegetation – very long lived
and dikaryotic
hyphae of the mycelium are septate
and coenocytic at specific stages
during their reproduction
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
The Common Mushroom
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the basidiomycotes
include the common
mushroom
basidium = “little
pedestal”
note the cap (pileus)
with the gills on the
underside
the supporting stalk =
stipe
fruiting body or
basidiocarp = cap + stalk
as in the ascomycotes
and its ascocarp – the
basidiocarp is an
aggregation of hyphae
pileus
basidiocarp
stipe
stipe
gills
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sexual reproduction:
like ascomycotes – basidiomycotes are heterothallic - + and – mating type hyphae
two haploid mating types undergo plasmogamy and a dikaryotic mycelium forms
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rain or temperature changes induce the dikaryotic mycelium to form the basidiocarp (mushroom)
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very fast growing
these “children” hyphae crowd out the parents and are long lived
still dikaryotic – no nuclear fusion yet (nuclei are still separated and are haploid)
basidiocarps can “sprout up” within hours in the rain
the gills of the basidiocarp become lined with dikaryotic cells called basidia
karyogamy occurs - within each basidium two nuclei fuse
meiosis results in 4 haploid nuclei total per basidium
each haploid nuclei develops into a basidispore
the basidiospores are located at the tips of the basidium
basidiospores are released when mature and are carried by the wind – germinate into new mycelia which
Dikaryotic
PLASMOGAMY
rapidly undergo more sexual reproduction
mycelium
Mating
type (–)
Haploid
mycelia
Mating
type (+)
SEXUAL
REPRODUCTION
Gills lined
with
basidia
Basidiocarp
(dikaryotic)
Dispersal and
germination
Basidiospores
Basidium with
four appendages
Basidium
Basidium containing
four haploid nuclei
Basidia
(dikaryotic)
KARYOGAMY
MEIOSIS
basidiospores
1 µm
Basidiospore
Diploid
nuclei
Key
Haploid (n)
Dikaryotic (n + n)
spore center of mass
sterigma
center of mass moves
Spore
Spore dispersal in
mushrooms
water film around
spore wall
water film
apiculus
water droplet
increasing water droplet
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basidiospore dispersal can be quite explosive – e.g. puffballs
basidiospore is attached to the gill via a sterigma – area of attachment is called an apiculus
dispersal mechanism:
1. air is humid between the gills and the spore is covered with a thin film of water
2. the spore secretes a small amount of sugar at the apiculus - the sugar picks up the air moisture and
the water condenses to form a drop
3. the increasing size of the water droplet draws the spores center of mass toward the apiculus
the water drop eventually disappears into the water film around the spore wall
4. the spore center of mass quickly turns away from the apiculus and the spore accelerates in that
direction – spore dispersal
the spore drops down from the gills & air currents know carry the spore away from the mushroom
Fungi as Decomposers
• fungi are well-adapted decomposers of
organic material
• very good at decomposing the
polysaccharides cellulose and lignin (plants &
wood)
• their decomposition makes available to
ecosystems inorganic nutrients such as
carbon, nitrogen and phosphate ions
Fungal Associations
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fungi can form mutualistic relationships
with plants, algae and animals
Fungal-Plant associations: formation of
mycorrhizal associations with the roots
of vascular plants
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these fungi are called mycorrhizal
all plant species harbor symbiotic fungi called
endophytes
these live harmlessly inside the leaves of
plants
most as ascomycetes
benefit certain grasses and other non-woody
plants by making toxins to deter herbivores
can also increase the plants tolerance to heat,
drought or heavy metals
Fungal-Animal associations: some
fungus share their digestive services
with animals
– assist in the breakdown of plant
material
– guts of cattle and other grazing
mammals
– some insects (termites and ants) can
raise “farms” of fungi to aid in digestion
– called farmer insects
leaf cutter ants depend on fungi to convert
plant material into something these ants can digest
Fungal Associations
Lichens: 25,000 species
– fungus + green algae (or cyanobacteria)
– produce a unique superorganism
– each requires one another to colonize areas
they wouldn’t be able to alone
– algae provide organic compounds, the
cyanobacteria fix nitrogen
– algae nestle among the fungal hyphae
– found from the arctic to the tropics
– most reproduce asexually
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asexual reproduction:
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either through fragmentation propagates new
lichens
or by the formation of soredia – small clusters of
hyphae with embedded algae - may be carried by
the wind to new locations
some sexual reproduction can occur through the
formation of basidiocarps or ascocarps
A fruticose (shrub-like) lichen
A foliose (leaf-like) lichen
Crustose (crust-like) lichens
Ascocarp of fungus
Soredia
Fungal
hyphae
Algal
layer
types of lichens:
– 1. Crustose lichens – grow as a crust on a
surface
– 2. Foliose lichens – leafy in appearance
– 3. Fructicose lichens – shrublike with
branching and intertwined fibrous parts
Algal cell
Fungal hyphae
10 µm
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Practical uses of Fungi
• popular as foods – mushrooms and morels and puffballs
• distinctive flavors of cheeses – blue cheeses – come from the fungi used to ripen
them
• soft drink industry uses Aspergillus to produce citric acid for colas
• we use yeasts and their fermentative processes to produce alcohol from sugar
• yeast fermentation is also used to produce carbon dioxide which is used in the
“rising” of breads – Saccharomyces cerevisiae
• use of Saccharo. yeasts in research labs is exploited to determine genetic
mechanisms that are also present in higher eukaryotes
• use of fungi to synthesize glycoproteins in large quantities (cannot be performed
by bacteria – lack the enzymes needed)
• fungi have medicinal value – ergot (poison) components can reduce high blood
pressure and to stop bleeding after childbirth
• some fungi produce antibiotics – penicillin produced by the ascomycete mold
called Penicillium
• the decomposing function of Phanerochaete chrysosporium is being studied in
order to determine how to make paper pulp
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fungal contamination of a bacterial plate – area surrounding the fungus is
free of bacteria
fungus capable of producing anti-bacterial substances = antibiotics
penicillin found on rotting oranges & its antibacterial actions on Gram +ve
bacteria first attributed to Alexander Fleming in 1928
– Fleming coined the term "penicillin" to describe the filtrate of a broth
culture of the Penicillium mold
1939, Australian scientist Howard Walter Florey and a team of researchers
demonstrated the in vivo bactericidal action of penicillin
1942: John Bumstead and Orvan Hess became the first in the world to
successfully treat a patient using penicillin
mass-produced in 1944 upon discovery of structure (1940 - Dorothy
Crowfoot Hodgkin)
World War II – penicillin saved an estimated 12-15% of lives.
– difficulty of manufacturing large quantities of penicillin and by the
rapid renal clearance of the drug necessitating frequent dosing
– became common procedure to collect the urine from patients being
treated so that the penicillin could be isolated and reused
penicillin is classified as a b-lactam antibiotic
– works by inhibiting the formation of peptidoglycan cross links in the
bacterial cell wall.
search for derivatives of penicillin : first major development was ampicillin
with a broader spectrum of activity
– further development: beta-lactamase-resistant penicillins including
amoxocillin, flucloxacillin, dicloxacillin and methicillin
– these penicillins are still ineffective against the methicillin-resistant
Staphylococcus aureus strains
Penicillin
Staphylococcus
Penici
Zone
inhib
grow
Yeasts
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1500 species of unicellular fungi
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often a synonym for the species Saccharomyces cerevisiae
chemotrophs – convert carbohydrates into CO2 and alcohol
(fermentation)
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Candida albicans - yeast infections
athelete’s foot
also found in guts of mammal and insects
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most species are either obligate aerobes (for cellular respiration) or
anaerobic (fermentation)
are no species of obligate anaerobes
naturally occurring on skins of fruits & berries – even on the skin or
epithelial linings of humans
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not a single taxonomic or phylogenic grouping
many species – divided up between Phylum Ascomycota & Phylum
Basidiomycota
e.g. bees and ants
even in deep sea environments
exist as either diploid or haploid forms
asexual reproduction through budding or mitosis – occurs in both
haploid and diploid cells
sexual reproduction through the production of pheromones by two
mating types
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happens under stress – the haploid cells die, leaving the diploid cells
to undergo meiosis to form spores of two haploid mating typesalpha and “a” types
alpha-factor pheromone is attracted to and binds the “a” type yeast
– the a-factor pheromone is attracted to and binds the alpha type
yeast
two yeast cells meet and fuse – karyogamy results in a diploid cell
Fungi as Pathogens
• about 30% of the 100,000 species are parasites or pathogens
• mostly of plants
– e.g. cause of chestnut blight and pine pitch
– e.g. 10 to 50% of world fruit harvest is lost to fungus
• some that attack food crops produce human toxins
– Aspergillus (ascomycete) contaminates grains and peanuts – secretes
aflatoxins
– Claviceps purpurea (ascomycete) grows on rye plants – toxins cause
ergotism
• about 500 species parasitize animals
– Batrachochytrium dendrobatidis (chytrid) has killed the extinction or
decline of 200 frog species
• infection by a fungal parasite = mycosis
– skin mycoses include ring-link “ringworm” (ascomycetes) – known
more commonly as “Athlete’s foot”
– Candida albicans – normal inhabitant of the vaginal epithelium