Fungi-Friend or Foe Flashcards
Cordyceps: Friend / Foe
Active compounds:
cordycepin, cordymin, ergosterol
Nutritional Relationships
Mutualists-A mutually beneficial
relationship with host
PAR-ASITES-Growing as a parasite
on a host
PATHOGEN-Growth of parasite on
a host results in disease symptoms. All pathogens are parasites, but not all parasites are pathogens
Mycorrhiza improve growth
Most common symbiosis in the
world
Occurs in almost all plants to
overcome nutrient limitations of
each partner
Fungi extend the surface area
improving uptake of water and
nutrients
Mycorrhiza increase surface area
- Plants rely on mycorrhizas
for water and nutrients - Fungi acquire photosynthetic
sugars from plant
Benefits of relationship: - Growth in nutrient poor soil
- Drought resistance
- Pathogen protection
Lichen (~13,500 species)
Intimate associations between a
photosynthetic partner (a green
algae or a cyanobacterium)
Lichen symbiosis
The fungus -protects the photosynthetic cells and absorbs
mineral nutrients from trace levels in the environment.
The photosynthetic partner - provides the fungus with carbon nutrients
Tropism
Biotrophy (parasite)- Feed from specific living hosts without rapidly killing them
Pathogens
Necrotrophy-Kill host tissues as part of
the feeding process
Hemibiotrophy-Biotrophy that leads to
necrotrophy
Saprotrophy-Feed on dead organic
matter (most fungi)
Fungal parasites of plants
Fungal (or fungus-like) parasites of plants account for
more than 70% of all major crop diseases
Plant Infection
Appresoria: Special nutrient absorbing
structures to tap the hosts reserves
Biotrophic parasites
- Avoid causing host cell death
- Secure a continuous nutrient supply
Black Stem Rust fungi Powdery mildew fungi
e.g Sphaerotheca pannosa - Roses
Ascomycota
e.g Puccinia graminis - Wheat
Basidiomycota
Claviceps purpurea – Friend or Foe?
Holy Fire / At Anthony’s Fire
Linked to eating bread / beer /
animals grazing on infected grain
Convulsive ergotism: paranoia,
hallucinations, twitches and spasms
Gangrenous ergotism: loss of peripheral
sensation, oedema, loss of affected tissues
→ amputation
Claviceps purpurea – Ergot alkaloids
Potent mycotoxin: ergotamine
Moderate doses: Contraction of smooth
muscle fibers e.g. in small arteries.
Large doses: Sufferers “go berserk”
- Constricted blood supply - gangrene
-Ergots contain Ascospores
Regulatory limits 0.05% - 0.3% of
ergot in grain = grain too poisonous
for use.
Control: Crop rotation, fungicides,
sifting of sclerotia, deep ploughing,
breeding for resistance
5-10% grain loss
Claviceps purpurea – Friend or Foe?
- Midwives used ergot sclerotia
as an aid in child-birth– no
longer recommended - Dihydroergotamine used to
relieve migraines
Necrotrophic parasites
Fungal parasites produce toxins or degradative enzymes.
Bruised fruit is very susceptible
E.g. Botrytis cinerea
10–20% annual losses in strawberry yields
Hemibiotrophic Parasites
Phytophthora infestans (oomycota)
Entire fields may become blighted and die in a few days or a few weeks
The sporangium releases flagellated
zoospores that infect the leaves via
appressoria
Potato blight
Necrotrophic phase: Infected potato tubers are small with sunken
lesions, stained purple
or brown.→ secondary
bacterial infections
Epidemics depend on humidity & temperature during different stages
Irish Potato Famine 1840s
Destroyed the potato crops
of Ireland in the 1840s
Lead to the starvation of up
to one million people
And the emigration to the
rest of Europe and the USA.
Still accounts for about 15%
of world fungicides sale.
- Fungal parasites of humans
~200 fungal species
are known infect
humans or other
warm blooded
animals
Dermatophytic Fungi
40 fungal species of mitosporic fungi -asexual spores
e.g. Tinea pedis – Athletes foot caused by Trichophyton rubrum or
ringworm
- Grow in the dead, keratinsed tissues of the skin, nails and hair
- Metabolic products can induce an inflammatory response
Fungi hit the Immuno-compromised
- HIV patients
- Transplant patients
- Patients suffering from cancer
- Advanced diabetes
- Corticosteriod therapy
In immuno-compromised individuals there is a
significant chance of infection from fungi that
normally do not pose a serious threat
Candida albicans: Healthy microbiota
Oral Candidiasis (thrush)
A 1st sign of AIDS in HIV
infected individuals
Dimorphic yeast
* Single cell form colonises the
mucosa
* Filamentous hyphal form can
penetrate the body tissues
Aspergillus fumigatus
- Common airborne
fungus; grows on
compost and in soil. - Mitosporic fungi -
Tiny spores are inhaled - Significant invasive
fungi in deep surgical
procedures and people
with existing
respiratory conditions (e.g. COPD, Cystic Fibrosis (CF)
Aspergillosis
Allergic bronchopulmonary aspergillosis (ABPA).
According to UK CF Registry 2018: 15% of people with Cystic fibrosis
were living with chronic Aspergillus infection, 7% more than 2008.
Pneumocystis jirovecii: yeast-like
- Commonly inhaled and cleared by immune system
- Pneumonea in late-stage HIV patients (Overgrowth in lungs;
blocking alveoli and spreading throughout body)
Cryptococcus fungi
Life threatening in people with impaired immune defences
Cryptococcal meningoencephalitis >15% of HIV-related deaths worldwide
Fungal Saprotrophs
Fungi are the most important recyclers of organic matter. Many produce enzymes that degrade complex polymers
Aflatoxins – Aspergillus flavus
- Commonly produced in stored
crops (groundnuts; cottonseed ..) - Aflatoxin is among the most
potent of all known carcinogens
Produce mycotoxin
(Aflatoxin)
Food must contain < 20 ppb
Sooty moulds e.g Cladosporidium
Mitosporic fungi
* Commonly grow on kitchen
and bathroom walls
* Natural habitat: leaf surfaces
/ decaying stalk tissues
* Utilizes soluble cellulose in
paints & wall-paper pastes.
* Difficult to eradicate
Serpula lacrymans: Dry rot
Building eaters
Basidiomycete
Breaks down cellulose in wood
Edible Basidiomycota
Much of the mushroom growing
industry is based on strains of the
common cultivated mushroom
Agaricus bisporus (or A.
brunnescens)
Bakers Yeast
Saccharomyces cerevisiae
Ferments glucose to produce:
-carbon dioxide for raising dough
- alcohol for making beer and wine
Cheese
Penicillium roqueforti is used
in the later stages of
production of the blue-veined
cheeses such as Stilton and
Roquefort.
It imparts a characteristic
flavour
Delicious “smelly” cheese!
Penicillium camemberti is
used to produce the soft
cheeses such as Camembert
and bries
Growth on surface forms a
“crust”
Produces proteases which
degrade the cheese to the soft
consistency.
Mycoprotein
Major development in recent years. An entirely new type of food:
Single cell protein:
-High protein content
- Low fat content
- No cholesterol.
QuornTM is made from fungus
Fusarium venenatum in a large
fermentation vessel. The fungal
hyphae are harvested and
processed into meat like chunks
Biofuels
Pretreatement to break down cellulose and hemicellulose to liberate sugars (Lignin-degrading fungi)——> Enzymatic treatment to make into suitable substrate for efficient fermentation———–> Fermentation by bacteria or yeast (Saccharomyces cerevisiae) —–> Ethanol fuel
Aspergillus niger
Produces 95% of the commercial production of:
Pectic enzymes to clarify fruit juices.
Amalyse
Starch → maltose in bread making.
Rennet to coagulate milk for cheese-making.
Citric Acid fizzy drink flavour
Antibiotics
- 1928 - Alexander Fleming, discovered Penicillin from
the fungus Penicillium notatum (P. chrysogenum)
Therapeutics
Secondary metabolites often produced by
microorganisms during stationary phase. Not
required for growth.
- Antibiotics
- *Statins
- Anti-tumour agents
- Immunosuppressors
* Statins – isolated from fungi Penecillium citrinum – reduction in
cholesterol levels. Taken by ¼ all people >45 in USA
Summary
- Fungi come in many shapes and
sizes - They share many common
structural and reproductive
features - Many strategies for nutrient
acquisition and dispersal have
evolved.
Pilobolus ballistic sporangium
