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Summary MBY261 Theme 1-7
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MBY 261: THEME 1Introduction to fungi
What are Fungi?
- Fungi are not plants (they are more closely related to animals)
- Large group of eukaryotic organisms
- Own kingdom (separate from plants and animals)
- Share a common ancestor with animals
- “Hidden kingdom” – most of the fungi on earth have not yet been discovered
o living body (thallus) made out of microscopic tubular cells (hyphae)
o Mycelia = mass of branched hyphae
o Mycelia usually hidden in soil, wood or other food source
o a mycelium can fill a single ant or cover many acres (can grow 1km per day)
Characteristic features of True Fungi (Mycota/Eumycota)
- Eukaryotic
- Grow as hyphae with apical growth (the organism grow from the tip/apex only)
- Dimorphic (sometimes grow as single-celled yeasts and hyphae) – switches from one growth pattern to another.
- Heterotrophic (depend on pre-formed organic nutrients) – cannot make own food
- Haploid nuclei – only one set of chromosomes
Characteristic features of Fungi
- Walls composed primarily of chitin and glucans (distinguishing factor)
- Absorb soluble nutrients trough the cell wall and plasma membrane
- Reproduce by both sexual and asexual means
- Produce spores
- Fruiting bodies (mushroom)
The Fungal Cell Wall
- Surrounds the fungal cell outside of the plasma membrane
- Dynamic structure that protects the cell from osmotic pressure and other environmental stresses
- Fungal cell wall allows cell to interact with environment
- Primarily composed of chitin, glucans, mannans and glycoproteins
- Chitin, which is extruded by the plasma membrane, is the largest component of the wall.
- Glucans, a type of polysaccharide, give the wall rigidity.
- Proteins, particular mannans, reside in the fungal cell wall and work as enzymes to synthesize more of
the cell wall.
- True fungi do not have cellulose in their cell walls
,Fungi in the “Tree of Life”
- Basis is to ID genes that are present in all living organisms and that have an essential role (highly
conserved) and only undergo small changes (mutations) over large periods of time.
- Comparisons of these gene sequences can then indicate relationships between organisms.
- Good candidates are genes that code for rRNA (ribosomes are sites of protein synthesis)
- Three different sizes of rRNA (23, 16, 5 in prokaryotes and 28, 18 and 5.8S in eukaryotes)
Tree of Life Web project
- collaborative effort of biologists and nature enthusiasts from around the world
- project provides information about biodiversity, the characteristics of different groups of organisms, and their evolutionary
history
- Aim is to link all main types of organisms on Earth based on phylogenetic relationships
- Generate phylogenetic trees
- Three evolutionary distinct groups (domains) – Bacteria, Arachea and Eukaryotes
- Uncertainty about levels below domains (Kingdoms)
- Animals, plants and fungi = “Crown Eukaryotes” clustered at the top
- Earliest fossil records for fungi – 460 - 455 million years age
- Fungi are more closely related to animals than plants
,Major Activities of Fungi
- Fungi are grouped according to how they obtain nutrients – parasite/pathogen, symbionts or
saprotrophs
Fungal pathogens of plants
- Obtain some or all nutrients from plants
- Host specific or more general
- Obligate parasite (can only grow in host tissue ; not in culture)
- Biotrophic = feed from living host cells
- Necrotrophic = kill host cells as part of feeding process (toxins & degradative
enzymes)
- Examples:
o Botrytis cinerea – soft rot on strawberry
o Ophiostoma novo-ulmi – Dutch elm disease
Fungal symbionts of plants
- Both partners benefit
- Lichens – associations between photosynthetic partner (algae) and a fungus
- Mycorrhizas – between fungi and plant roots
- Endophytic fungi – fungi within plant walls and intercellular spaces
Fungal pathogens of humans
- Only approximately 200 spp.
- Humans have innate immunity
- Except when immune system is compromised
- Most common infections are dermatophytic fungi
Fungi as biocontrol
- Fungi parasitize other fungi, insects and nematodes
- Possible disease control
Fungal saprotrophs
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Fungi in Biotechnology
- Food and food flavouring
o mushrooms (Pleurotus ostreatus, Agaricus bisporus)
o cheese (Pennicillium camemberti)
- Metabolites (Secondary)
o antibiotics, gluconic acid, ciclosporin, ergot alkaloids
- Enzymes
o Pectic enzymes to clarify fruit juice, alchol oxidase as bleaching agent
- Heterologous gene products
o Saccaharomyces cerevisiae used as “factory” to produce pharmaceutical products (Eg.
Hepatatis b vaccine)
, Tolypocladium inflatum
- Produces cyclosporin and efrapeptins
- Insecticidal and antifungal properties as well as being an immunosuppressant
- Ascomycete fungus (Produces asci with 8 ascospores)
- Originally isolated from soil in Norway
- Pathogen of scarab beetles that evolved to also survive as a facultative saprobe
- Morphological characteristics include: spherical swollen phialides, unicellular conidia that are borne in a slimy head
- During the sexual stage ascocarps (asci with 8 ascospores) are produced on the insect cadaver
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