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Fungus Notes
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Lecture notes on Fungus, including: Chytrids, Zygomycetes, Basidiomycetes, Ascomycetes, morphology, reproduction, moulds, biotechnology applications
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FUNGI- Aspergillus niger: production of citric acid, used in soft drinks and as a general acidifier
EDIBLE MUSHROOMS
- The edible part is the sexual fruiting body
- Most edible mushrooms belong to the basidiomycetes, only some exceptions from
ascomycetes
- some fungi may be highly toxic: e.g. amantia phalloides (death cap)
MOULDS AND PATHOGENS
- sometimes produce harmful mycotoxins
- colour of mould fungi derives from asexual spores on top of colonies
- colour surrounding a colony or staining the mycelium may derive from toxic secondary
metabolites
- absence of colour is not a sign of lack of toxins as a lot of toxins are colourless
- e.g. Fusarium solani : potato dry rot
- E.g. Fusarium garminerarum (head blight of wheat and corn)
- E.g. botrytis cinerea (fruit rot)
EXPLOITATION OF FUNGI
- Production of extracellular proteins (cellulases, amylases, pectinases)
- Production of additives (citric acid, itaconic acid)
- Production of food (soy sauce, sake, cheese)
- Fermenatation (beer, wine)
- Production of antibiotics and drugs (penicillin- from penicillium notatum, lovastatin)
(secondary metabolites)
POSITION OF FUNGI ON THE TREE OF LIFE
- Earth formed approx. 4.55 billion ears ago
- Estimates start of life on eath approc 3.8 billion years ago
- Approx. 3.2 billion years ago the first photosynthesis may have occurred
- 2 billion years ago the first eukaryotic cells formation of the three lineages of the kindoms
plant, fungi and animal approx. 1.5 billion years ago
- Mushroom fruiting bodies are soft fleshy and easily degradable which contradicts fossil
formation
- Mushrooms appear more closely related to animals
- A sister branch to the fungi are the nuclearia which are amoeboid protists that beed on algae
and bacteria (grow phagotrophically on algae and bacteria)
- The most basal fungi are rozella and microsporidia which are both generalky not free living
but are important endoparasites, they do not form complex multicellular structures
OOMYCETES (egg fungi or water moulds)
- Not true fungi
- Belong in the SAR group to the Stramenopiles which are more closely related to brown algae
than to fungi
- Morphological appearance dimilar to fungi but do not belong to this kingdom
- Cell wall contains cellulose (as in plants)
, - Closely related to brown algae and diatoms
- Comprise very important pathoogens
- Phytophtora infestans- potato pathogen responsible for the irish potato famile
- Saprolegnia: causes huge problems in salmon farming
- Other species cause trees to die
TRUE FUNGI
- Chytrids
- Zygomycetes
- Basidiomycetes (also called modern fungi)
- Ascomycetes (also called modern fungi)
- Glomeromycotan (sister group to ascomycetes)
- Sexual reproduction is used for morphological differentiation of fungal lineages
NUTRITION AND SHAPE
- Feed mainly by absorption (digestion of insoluble material outside)
- Fungi cannot ingest food due to the rigid cell wall food needs to be solubulised outside to
the cell to be taken up by absorption
- All fungi are heterotrophic eat organic matter produced by others
- Secrete enzymes to digest nutrients outside and absorb the solubilised compounds
- Have very diverse life style : decomposers (live on dead organic material), parasites (absorb
nutrients from living hosts and may cause disease), symbiotic (live in mutually beneficial
relationship with other organisms)
DIFFERENCES BETWEEN PLANT AND FUNGAL CELLS
- Main composition of plant cell walls: cellulose fibrils, pectin, glycans, and depending on the
cell wall lignin’s
- Nomenclature of cell wall polymers: when glucose is in it’s open linear form it is not stable in
aqueous solution and spontaneously forms a ring closure between the aldehyde group on
carbon atom 1 and the alcohol group on carbon 5 forming a pyranose ring closure.
Depending on the site of attack during ring formation the resulting pyranose is either alpha
form or beta form (relates to the positioning of the hydroxyl group on carbon 1)
- Cellulose makes up approx. 50% of plant cell wall. Made from the beta form of glucose
- Cellulose is produced by a beta-1,4-glycosidic linkage of glucose molecules
- Main composition of fungal cell walls: does not contain cellulose, instead has rigid chitin
layer followed by beta-glucans with 1,3 or 1,6 linkage and sugar containing surface proteins
(mannoproteins). Also produce varying amount of alpha glucans
- Mannoproteins= mannose-containing glycoproteins
- Similar to cellulose, beta 1,3 and 1,6 are produced from glucose with ring closure in the beta
form, linakge occurs either between hygroxyl groups of C1 and C3 or C1 and C6. Combination
of both forms of linkage leads to branching of the glucan chain
- Chitin and chitosan: made up of N-acetylglucosamine in a b-1,4 linkage
- Deactylated chitin= chitosan
- In glucosamine the OH group in position C2 is replaced by an amino goup chemical
properties of chitin very different to cellulose
- When glucosamine is used rather then N-acetylglucosamine result is chitosan
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