Fungal Growth and Morphogenesis II Flashcards
How do fungi form relationships with other organisms?
- Fungi interact with each other and other organisms – microbes, plants and animals.
- Competition and antagonism occur in natural populations.
- More specific interactions are pathogenic and symbiotic.
- Hyphal growth is a determinant of all such interactions.
Fungus- fungus interactions?
Verticillium biguttatum - a mycoparasite and invades hyphae of other fungi.
Germinating spores of V. biguttatum show tropism towards host hyphae, leading to penetration and production of club-shaped haustoria (nutrient-absorbing structures) within the living host hyphae.
Verticillium grows over the host colony and kills the older parasitised cells but produces new haustoria at the advancing edge of the infection.
Spores can sense another org.
Interactions with mycorrhizas?
- A beneficial symbiotic relationship between plant roots and fungi.
- Extremely common - over 80% of plant species have mycorrhizas including crops like cereals, peas, tomatoes, onions, and apples etc, as well as wild plants.
Will produce fruiting bodies (mushrooms and toadstools).
- Mycobiont obtains carbohydrates, vitamins, and spore germination stimulated by root exudates.
- Plant obtains phosphorus, nitrogen and trace metals, increased water uptake and protection from root pathogens.
What are types of mycorrhizas?
A - Ectotrophic of forest trees – sheath and limited root invasion (Hartig net).
On surface.
B - Arbuscular of many herbaceous plants and tropical trees – arbuscles and vesicles in host cells.
Hyphae- intracellular penetration.
Vesicles inside cells.
C - Endotrophic of orchids – active and digested cells within host root.
Penetrate cells.
Cells can use them as a food source.
Interactions with lichens?
- Lichen definition - an association between a fungus and a photosynthetic partner. fungal growth form.
- Mycobiont - the fungal partner in a lichen.
- Photobiont - the photosynthetic partner in a lichen; either a green alga or cyanobacterium. Rarely, it is both.
- Mutualistic partnership – photobiont secretes carbohydrates, fungus provides holdfast.
The green alga Trebouxia accounts for >75% of known lichens. 10% of lichens have a cyanobacterium as the only or primary photobiont; most of these are Nostoc sp. Nitrogen fixing due to heterocysts.
Fungal components are differentiated hyphae.
Close association of algae/bac and fungus- algae/bac “trapped” by fungus.
Rhizines- fungal analogy of roots.
Lichen thalli?
•Unique discrete form that bears no resemblance to non-lichenized alga or fungus.
•Slow-growing:
- most grow
Distribution of lichens?
- Worldwide, in some of the most extreme environments, from the Arctic to Antarctic, deserts to tropics.
- Occur on soil, plants, animals, on or in rock, and on man-made structures.
•Mainly in rural areas rather than cities:
–Lichens are intolerant of atmospheric pollution, particularly sulphur dioxide.
Estimated 17000 species found almost everywhere where they function in weathering and soil formation as well as being a winter food source for, e.g. reindeer.
Interaction with plant pathogens?
Fungi account for ~70% of all major plant diseases, e.g. potato blight, Dutch elm disease, take-all disease of cereals, root rots.
Mildews, rusts- Complicated life cycles.
Potato blight- org. is an oomycete, not a fungus.
What are some serious crop diseases?
•Magnaporthe grisea (rice blast):
- 11-33% of rice harvest destroyed per annum (157 million tonnes of rice).
•Erysiphe graminis:(powdery mildew of barley and wheat)
- >£400 million p.a. fungicide market.
•Septoria tritici ( blotch disease of wheat):
- >£250 million p.a. fungicide market.
•Phytophthora infestans
- >£100 million p.a. fungicide market.
What are plant infection processes?
- Natural plant openings - stomata, lenticels. Pathogens can sense where these are for infection.
- Wounds.
- Direct penetration of the cuticle:
- enzymatic action - cutinase (methyl esterase).
- mechanical force eg. hyphal tip.
Many fungi produce specialised infection cells: Magnaporthe grisea – rice blast fungus:
Appressorium- Specialised infection structure. Appressorium forms penetration peg.
Collapsed conidium
(spore).
Wood rotting fungi?
Wood - one of the most abundant energy sources in nature but difficult to degrade – except for fungi. Fungi are only living organisms that can break down lignin (ie. wood).
While some are tree pathogens and can also rot building materials, in the biosphere they are of major importance for nutrient cycling.
Hyphae can aggregate and form visible strands.
Brown rot fungi - degrade cellulose and hemicellulose but leave lignin, e.g. dry rot fungus. Differentiated hyphae- can grow long distances.
Some hyphae are like blood vessels.
Not good with high temp.s.
White rot fungi - degrade all components even lignin, e.g. Armillaria, the honey fungus. Degradation of organic pollutants.
Interaction with humans?
Several human pathogens…thrush, ringworm and athlete’s foot all caused by fungi.
Not as many as bacteria or viruses.
Many are just irritants- not usually life threatening.
What are some serious human pathogens?
•Aspergillus fumigatus
- inhaled spores, lung infection, often fatal in immuno-compromised patients.
•Cryptococcus neoformans:
- meningitis, often fatal.
•Candida albicans:
- Thrush, skin and vaginal infections.
- blood-borne infection can be fatal.
- Partly related to Aspergillus- hosptial acquired infection.
•Histoplasma capsulatum
- Histoplasmosis.
Candida albicans?
3 in 4 women will get at least one Candida (thrush) infection.
One in ten hospital patients will get a Candida infection (>80% AIDS patients).
One third of cancer patients, organ and bone marrow transplant patients get Candida blood infection.
There are very few antifungal antibiotics and drugs.
Fungus is eukaryotic- difficult to find a target selective enough so it doesn’t kill human cells.
Get engulfed by macrophages, then grow hyphae out of them. Kill macrophages.
Stalks grow from mycelium.
Chains of spores.
What are the main sites of infection following dissemination from the lung?
1 - Brain (10% - 20%). 2 - GI tract (40% - 50%). 3 - Heart (15%). 4 - Kidney (30%). 5 - Liver/spleen (30%). 6 - Skin (5%).
