Fungi General Concepts

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FungiGeneral Concepts
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What is a fungus?

• Heterotropic organism devoid of chlorophyll
• Has cell walls
• Non motile (exception is zoospores)
• Reproduces by spores
• Primary storage product is glycogen
• Usually filamentous, eukaryotic and multicellular

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Kingdom Fungi overview

• unicellular to multicellular
• cell walls primarily chitin
• heterotrophic
• secrete digestive enzymes (external digestion)
• important decomposers

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Kingdom Fungi overview

• if multicellular
• hyphae long, slender filaments of cells
• mycelium mass of hyphae

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Kingdom Fungi classification

• Four Major Groups of Fungi
• Phylum Zygomycota
• Phylum Ascomycota sac fungi
• Phylum Basidiomycota club fungi
• Imperfect Fungi asexual reproduction only

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Phylum Zygomycota

• defined by special structure for sexual
  reproduction a resistant ball called a
  zygosporangium where meiosis occurs and
  meiospores are formed
• mainly asexual reproduction (conidia,
  conidiophores)

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Phylum Zygomycota

• includes bread molds
• look at the example, Rhizopus

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Phylum Ascomycota sac fungi

• defined by ascus (sac-like sporangium)
• karyogamy occurs to form zygote
• meiosis forms ascospores in a sac
• sac breaks open to release spores
• asexual reproduction common as well

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Phylum Ascomycota sac fungi
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Types of Ascomycetes
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Phylum Basidiomycota club fungi

• includes mushrooms, toadstools, shelf fungi,
  stinkhorns, and puffballs
• defined by basidium (club-like sporangium)
• karyogamy occurs to form zygote
• meiosis forms basidiospores at tip of club
• spores pinch off from club for release
• little asexual reproduction

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Imperfect Fungi

• fungi with no known sexual reproduction (only
  asexual)
• Slides
• 2-3 Penicillium
• 2-4 Aspergillus
• observe conidiophores and conidia also note
  septate (cross-walled)

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lichens

• symbiotic relationship between
• a heterotrophic fungus (mycobiont)
• and an autotrophic alga or bacterium (photobiont)
• usually mutualistic (both benefit)
• fungi offer shelter from the harsh environment
• photobiont produces food through photosynthesis

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lichens

• There are three forms of lichens
• crustose- crustlike
• foliose- leaflike
• fruticose- shrublike, or fruitlike
• be able to identify the three forms

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Kingdom Fungi reproduction

• reproduction mainly by spores (both sexual and
  asexual)
• spores somewhat resistant to harsh environmental
  conditions
• spore germination mainly upon exposure to water

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Kingdom Fungi reproduction

• sexual spore terms vary
• asexual spores conidia, formed on conidiophores

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Kingdom Fungi reproduction

• Asexual- (imperfect stage)
• spores formed by mitosis
• some fungi exhibit only asexual reproduction
  (imperfect fungi)

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Asexual spores

• Chlamydospores are thick walled thallic conidia
  that function as a resting spore
• Asexual spores are either sporangiospores or
  conidia.

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Sporangiospores vs. Conidia

• Sporangiospores are borne in a sac called a
  sporangium. The cytoplasm within the sac is
  cleaved into sporangiospores. The sporangium is
  borne on a specialized hypha known as a
  sporangiophore.
• A conidium is borne on the tip or side of a
  specialized hypha known as a conidiophore.

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Kingdom Fungi reproduction

• Sexual- (perfect stage)
• gametes are produced in the gametangia
• zygotic meiosis, with modifications.

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Sex Spores in Fungi
Zygospore
Oospore
Ascospores
Basidiospores
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Zygotic Meiosis zygote directly undergoes
meiosis
mitosis
gametes
1N
1N
1N
2N
2N
(zygote)
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Kingdom Fungi reproduction

• zygotic meiosis, with modifications.
• plasmogamy
• cells fuse their plasma membranes
• results in dikaryotic cells if nuclei do not fuse
  (NN instead of true diploid)
• karyogamy
• nuclei fuse, making a true diploid (2N)
• this makes the zygote that undergoes meiosis

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How do fungi live?

• Fungi feed by absorbing nutrients from the
  organic material that they live in.
• They digest their food before they absorb it by
  secreting acids and hydrolytic enzymes.
• Different fungi have evolved to live on various
  types of organic matter, some live on plants
  eg.Phytopthora infestans - the potato blight
  fungus, as seen here
• Some live on animals eg.the athlete's
  foot fungus and some live on insects
  eg.Cordyceps australis.

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Interesting fungi

• One of the largest living organisms in the world
  is a specimen of the fungus Armillaria ostoyae
  which covers 1,500 acres in Washington State, USA
  and seems to be 400-1,000 years old.
• The only evidence of the fungus are clumps of
  golden mushrooms that pop up in autumn when it
  rains. Largely this fungus is seen underground
  and forms huge rhizomorphs (root like structure).

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Helpful fungi

• Most of us use fungi every day without knowing
  it. We eat mushrooms and Quorn (a vegetarian
  fungal protein), but we also prepare many other
  foods using fungi.
• The yeast Saccharomyces cerevisiae is used to
  ferment sugar to alcohol and carbon dioxide the
  process used to make beer and wine and also to
  make bread rise.
• The fungi Aspergillus oryzae and Aspergillus
  sojae are used in the production of the oriental
  foods soy sauce and miso. We also use fungi to
  produce flavourings, vitamins and enzymes and to
  mature many cheeses.
• Fungi play an essential role in both the
  Nitrogen and Carbon cycle by breaking down dead
  organic material.

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Importance of fungi

• Without fungi we would not have bread, beer, wine
  or antibiotics, but more importantly without the
  nutrient recycling and plant nutrition provided
  by fungi - we probably could not survive at all.
• In humans, fungi cause skin infections such as
  ringworm and athlete's foot, but they also cause
  several deadly diseases which can be hard to
  treat. Fungi that can cause life-threatening
  infections in people include Aspergillus
  fumigatus, Candida albicans and Cryptococcus
  neoformans they are called pathogens.
• Ringworm infection on leg

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• What is Aspergillus?
• It is a genus of around 200 fungi (moulds) found
  worldwide.
• Fungi are identified in the lab by their
  structure and appearance. They may appear as
  round single cells like yeast, or made of chains
  of cells called hyphae.
• Aspergillus is a filamentous fungus as opposed
  to yeast which is single celled.
• Fungi reproduce by forming tiny spores which can
  easily be airborne.
• Conidial head or fruiting body of
  Aspergillus - producing spores

Yeast
Aspergillus hyphae
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• Why is Aspergillus important?The following
  slides focus on Aspergillus because this fungus
  illustrates a spectrum of positive and negative
  aspects of fungi with respect to the environment
  and disease.
• Some Aspergillus species cause serious disease in
  humans and animals it is pathogenic.
• Some Aspergillus species produce enzymes which
  have important industrial applications.
• Aspergillus can produce mycotoxins these are
  often found in contaminated foodstuff and are
  hazardous to the consumer.

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Importance of fungi?

• Most patients with deadly fungal diseases do not
  have a fully functional immune system. They may
  have leukaemia or AIDS or they may be taking
  drugs to suppress their immune system because of
  organ transplantation.Although there are drugs
  to treat fungal infections these drugs can have
  some nasty side-effects because they are often
  toxic to people as well as to fungi. There is a
  desperate need for new and better anti-fungal
  agents.
• Aspergillus fumigatusspore forming head
  (Electron micrograph)

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Aspergillus as a pathogen in man-

• Aspergillosis is a group of diseases caused by
  Aspergillus. The symptoms fever, a cough, chest
  pain or breathlessness occur in many other
  illnesses so diagnosis can be hard. Usually only
  patients with already weakened immune systems or
  who suffer other lung conditions are
  susceptible.
• In man the major forms of disease are
• Allergic aspergillosis (affects asthma, cystic
  fibrosis and sinusitis patients).
• Acute invasive aspergillosis (risk increases if
  patient has weakened immunity such as some cancer
  patients and those on chemotherapy).
• Disseminated invasive aspergillosis (widespread
  through body).

Aspergillus keratitis (eye)
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Helpful fungi

• We get some important drugs from fungi such as
  the antibiotic penicillin and cyclosporin A - a
  drug that stops organ rejection after
  transplantation.
• Research scientists use several fungi to
  investigate basic functions that occur in all
  cells because they are simple and easy to grow
  some cancer research is done using fungi.
• Fungi are responsible for breaking down dead
  organic matter which allows nutrients to be
  cycled through the ecosystem.