Transcript Microbiology

Fungi 1
Importance; Structure & Growth
Dr. Clem Kuek
ZIP\Lectures\Basic\Lectures\Fungi\Fungi1\Fungi1.ppt
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Fungi
Definition
Eucaryotic, spore-gearing organisms with absorptive nutrition, no
chlorophyll, and that reproduce sexually and asexually.
Includes
• Kingdom Fungi
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Lower fungi
Higher fungi
• Kingdom Protista

Slime molds (cellular and acellular)
Species
90,000 sp. described;
1.5 million spp. estimated to exist (Prescott et al., 1999).
Dr. Clem Kuek
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Fungi
Chemoorganotrophs
• Organic compounds as sources of carbon, electrons and energy.
• Most use carbohydrates and nitrogenous compounds to synthesize
their own amino acids and proteins.
Aerobes
• Usually aerobic;
• Some facultative anaerobes e.g. yeasts in alcoholic fermentation.
• Obligate anaerobes found in ruminants.
Most are saprophytes
• Extracellular hydrolytic enzymes; hydrolysis; absorption of hydrolyzed
products.
Dr. Clem Kuek
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Importance in the biosphere
Saprophytism
• Primary colonizers of plant litter
Most fungal species can feed on complex polymers
• Polymers
Long chain, branched and aromatic organic molecules such as
cellulose, pectin, lignin by basidiomycetes and ascomycetes.
• Small organic molecules
Sugars; fats; peptides by lower fungi and slime molds.
Dr. Clem Kuek
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Importance in the biosphere
Symbiosis
• Mycorrhiza (fungus/root)
e.g. wheat/Glomus sp.; pine/Leucopaxillus sp.
May/may not be obligate
May (endo-)/may not (ecto-) enter the host
Fungus receives plant photosynthate
Plant receives mineral nutrients and protection from pathogens
• Lichens (alga/fungus)
Sugars; fats; peptides by lower fungi and slime molds.
Dr. Clem Kuek
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Importance in the biosphere
Parasitism and predation
• Plants
 8,000 spp. of fungi cause disease
e.g. rusts and take all in wheat; potato blight
• Animals
 50 spp. of mostly opportunistic yeasts.
 Systemic mycoses of internal organs e.g. Candida albicans
candiasis of the intestinal thrush.
 Superficial mycoses e.g. Trichophyton spp. which cause ringworm
and athelete’s foot.
Nematode-trapping fungi.
Dr. Clem Kuek
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Importance in the biosphere
Mycotoxins
Secondary metabolites highly toxic to animals (ppm concentrations)
Examples
• Aflatoxin from Aspergillus flavus
A. flavus grows in maize and cereals under warm, moist storage; and
in peanut pods underground before harvest. Causes aflatoxicosis.
• Amanitin from Amanita muscaria
Toadstools (hallucinations; liver damage; death).
• Ergot alkaloids from Claviceps purpurea
Ergotism from ingestion of infected seedheads of rye and grasses.
Dr. Clem Kuek
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Importance in the biosphere
Industrial, food and agricultural uses
• Chemicals e.g. antibiotics; organic acids.
• Biomass e.g. mushroom; mycoprotein.
• Food fermentations e.g. tempe; cheese; alcohol production; bread; soy
sauce.
• Biocontrol agents e.g. mycoherbicides; mycoinsecticides.
Also see lectures on Agricultural Microbiology and Industrial Microbiology
Dr. Clem Kuek
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Importance in the biosphere
Biodegradation
Damage by saprophytes results in economic losses.
• Fungi are ubiquitous.
• Nutrients for saprophytic growth found in:
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Foodstuffs
Building materials
Textiles
Packaging
• Control measures based on imposition of unfavorable environment on
the fungus e.g. gas/vacuum packaging; chemical inhibitors; asepsis; water
activity; temperature control.
Dr. Clem Kuek
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Importance in the biosphere
Bioremediation
Reduction of waste materials by exploiting the biochemical
capability of the fungi e.g.
• Cellulosic materials e.g. composting
• Effluent treatment e.g. biobleaching
Dr. Clem Kuek
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Structure
Filamentous
• Hyphae
• Mycelium (pl. mycelia)
• Pseudomycelium (single-cells;
no cytoplasmic streaming)
Dimorphism
• Yeast form ↔ Mycelial form

YM shift
Septa
• Non-septate (coenocytic)
• Septate (acoenocytic)

Uni- or multiperforate septa
permits cytoplasmic streaming
Dr. Clem Kuek
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Growth
Filamentous fungi grow by hyphal extension
• Propagule
Hyphal tips; hyphal fragments;
spores
• Hypha/hyphae
Daughter cells by central
constriction and formation of
septa
• Mycelium (pl. mycelia)
• Colony (thallus)
Yeasts grow by budding
Dr. Clem Kuek
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Growth
Growth measured in
• Colony mass
• Colony diameter
To produce growth curves similar to that of the bacteria
Metabolic products typically occur at different stages of
the growth curve
Primary metabolite
Secondary metabolite
Biomass
Metabolite
Dr. Clem Kuek
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Growth
Fungi can propagate via
1. Hyphal fragmentaion
Lysis of aged parts of hyphae; other living sections to grow into new
colonies.
Mechanical breakage e.g. soil disturbance; break-up of substratum.
2. Sclerotia
Specialized hyphal propagules.
Storage and survival structure; resistant to extreme environmental
conditions.
Germinate to form new hyphae or sexual spores.
3. Rhizomorphs
Hyphal aggregations growing in parallel into rope-like structures a few
cm long and 1 – 2 mm thick.
Transports fungus to another part of the substratum e.g. rotting wood,
from where hyphae disperse and spread out.
Dr. Clem Kuek
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