Evolution and Diversity of Fungi Flashcards
Definition of fungi
Any group of unicellular, multicellular or multinucleate non-photosynthetic organisms feeding on organic matter, which includes moulds, yeast, mushrooms and toadstools
To be eukaryotic, organisms must have…
- membrane-enclosed nucleus
- DNA in chromosomes
- Meiosis and mitosis
- Organelles e.g. mitochondria, Golgi, endoplasmic reticulum
- A cytoskeleton
5 differences between fungi and plants
- Fungi are heterotrophs
- Fungi have filamentous bodies
- Fungi have usual reproductive modes
- Fungi have cell calls made of chitin
- Fungi have nuclear mitosis
Approximately how many fungal species are there?
1-3 million
What taxonomic ranking is fungi?
Kingdom
When did fungi separate from animals?
1 billion years ago
How do fungi obtain energy?
They use organic compounds as a carbon source - they are chemotrophs and acquire compounds by absorption
What are the fungal growth requirements?
Sugar
Nitrates
Sulphates
Iron
Some fungi are saprophytes. What is a saprophyte?
They utilise food from dead organic matter
What are two examples of parasitic fungi?
Necrotrophs - kill the host
Biotrophs - keep the host alive
What is the structure of fungi?
Exist mainly in the form of slender filaments (hyphae) or are unicellular (yeasts)
Describe hyphae growth
Long chains of cells joined end to end divided by cross-walls (septa)
Septa rarely form a complete barrier, they instead allow organelles and cytoplasm to move freely through the hyphae
A mycelium is a connected mass of hyphae that grows through and penetrates a substrate
What are the two types of yeast-like growth?
Budding (new organism develops from an outgrowth or bud due to cell division at a particular site)
Fission (division of one large cell to produce two identically sized cells)
What are the 5 components of a fungal cell wall? (going from the outside inwards)
- B-glucans
- Glycoprotein
- Proteins
- Chitin + protein
- Plasmalemma
What is the fibrillar component of oomycetes (not considered fungi)?
Cellulose, B-glucans
What are the fibrillar components of chytridiomycetes?
Chitin
Glucan
What are the fibrillar components of zygomycetes?
Chitin
Chitosan
What are the fibrillar components of Ascomycetes?
Chitin
B-glucans
What are the fibrillar components of Basidiomycetes?
Chitin
B-glucans
What is dimorphism growth?
Two or more growth forms
Fungi can switch between hyphae and yeast like growth depending on the environmental conditions
What are haustoria?
A projection from the hyphae of a parasitic fungus, which enters plant cells and takes their nutrients
What are oomycetes?
Hyphae-like growth but often with motile spores. Some produce conidia. However, they are no fungi as they have cellulose cell walls
Describe fungal reproduction
Fungi produce spores, which can be either single or multicellular structures
Asexual spores are called conidia
Sexual spores are named after the fungal group - asco-/basidio-/zygospore
Spores can remain dormant until conditions are optimal for survival
How are spores dispersed?
Wind Rain Flies Shock-waves Water-splash Water-pistol
What type of fungus has it’s spores dispersed by flies?
Phallus impudicus (stink horn)
What fungus spreads it’s spores with a shock wave?
Puffball fungus
What fungus dispersed it’s spores when water splashes it?
Cyathus sp. (birds nest)
Features of microsporidia
Primitive fungi that are intracellular parasites
Microsporidiosis occurs when a spore tube contacts the host cell and the cytoplasmic contents infect the host cells. These contents replicate and then cause cell lysis, releasing spores for reproduction
Why are microsporidia potentially the cause of bee decline?
They cause nosema, a disease affecting honey bees
What are the symptoms of a host infected with microsporidia?
Diahorrea, fever, reduced vigour
What is the other name for water moulds?
Chytridiomycetes
Features of chytridiomycetes
- Motile zoospores with flagella
- Rarely studied, the smallest and most primitive of the four phyla (now separated into four distinct phyla)
- Anaerobic
- Found in rumen of cattle where they help digest cellulose
What genus of chytridiomycetes is found in the rumen of cattle?
Neocallimastix sp.
What is an example of a typical species of chytridiomycete?
Allomyces macrogynus
Terminal gametangia are male and sub terminal gametangia are female
What are the features of Allomyces gametes?
- Female gametes released 2-3 minutes before male gametes to reduce chance of self-fertilisation
- Carotene pigment in male gametes gives gametangia orange colour
- Chemotaxis in the gametes
- Females release sirenin
- Males release parisin
What is frog chytrid?
Batrachochytrium dendrobatidis
Infects frog skin, causing loss of homeostasis
Poses a severe threat to from biodiversity
What is another name for pin moulds?
Zygomycetes
Features of zygomycetes
-Commonly encountered
-Sexual gametes are immobile
-Produces temporarily dormant zygosporangia
-Sexual reproduction occurs by fusion of gametangia
-Asexual reproduction is most common - hyphae produce clumps of erect stalks called sporangiophores, which form sporangia
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What are the two mating types of zygomycetes?
- Homothallic - self-fertile
2. Heterothallic - has different mating types and must mate with a compatible partner of a different type
What is a glomeromycete?
- Vecisular / arbuscular mycorrhizal fungi
- Roots about 90% of all vascular plants involved in mutualistic symbiotic relationships
- Only around 160 species found so far
- Many genetically different nuclei within the same mycelium
What are the two types of mycorrhizae formed by the plants?
- Endomycorrhizae - fungal hyphae penetrates outer cells of plant root. Most common and mainly found in glomeromycetes
- Ectomycorrhizae - hyphae surround, but do not penetrate, cell walls of roots - mainly Ascomycetes and Basidiomycetes
What is another name for sac fungi?
Ascomycetes
Features of Ascomycetes
- Produce sexual spores inside a sac-like cell then shoots the spores to disperse them
- Hyphae are usually septate (divided by cross walls)
- Sexual reproduction is by ascospores
How do Ascomycete hyphae respond to damage?
The septa have a pore which allows organelles and cytoplasm to move through the hyphae. If one of the hyphal cells is damaged, the Woronin bodies block the septal pore, preventing cytoplasm from being lost
Features of sexual reproduction in Ascomycetes
- Usually 8 ascospores, but sometimes 4, produced within the ascus
- Controlled by mating-type genes a and alpha
- Diploid cell divides by meiosis to give four ascospores inside an ascus
- When hyphae meet they swell up and a trichogyne forms between them
- The nuclei of one hypha migrates to the other hypha, forming pairs of nuclei
- At the tip of the hypha, a hook forms containing a pair of nuclei
- The nuclei go through a coordinated nuclear division, where they both undergo mitosis at the same time
- Septa are laid down dividing off the two hyphae in the crook of the top from the top of the tip and the rest of the hyphae
- The hyphal wall dissolves between the tip of the hook and the rest of the hypha, allowing the two remaining nuclei to reunite and continue to grow another hypha
- The two nuclei in the new hypha undergo karyogamy, forming a diploid nucleus
- This diploid nucleus undergoes meiosis I, meiosis II and then mitosis to form 8 ascospores within an ascus
What are the three types of asexual reproduction in ascomycetes?
Budding
Fission
Fragmentation
What are the two thick-walled resting spores of Ascomycetes? What are the they adapted for and what produces them?
Chlamydospores and conidia
Adapted to survive adverse environmental conditions
Produced by conidiophores (asexual reproductive bodies)
What is the name for spores stored within hyphae?
Endospores
What is the name for spores stored outside hyphae?
Exospores
What gives ascomycetes colour?
Hyphae are colourless so colour is provided by spores, which are coloured as an adaptation for better survival e.g. UV protection
What is the ascocarp?
The sexual fruiting body
What are ascospores?
The sexually derived spores
What’s is an ascus (plural asci)?
The sac that contains the ascospores
What is a conidium?
The asexual spore
How is grouping done in Ascomycetes?
According to sexual fruiting form
What are the 4 main groups of Ascomycetes? What are each of their sexual fruiting forms?
- Archiascomycetes - no specialised structure
- Plectomycetes - bell shaped fruiting body
- Pyrenomycetes - flask shaped (Perithecium), with an opening (operculum) growing from a basal mycelium
- Discomycetes - cup/disc shaped, with a supporting stalk. Asci produced on upper surface
How many cells is the diploid stage of an Ascomycete’s life cycle restricted to?
A few
What are lichens?
Associations between ascomycete fungi and algae, important in weathering rock surfaces allowing soil formation
What are soredia?
Propagules containing both fungus and algae together so new lichens can be established
What are endophytes?
Ascomycete fungi which grow inside plants and produce toxins to deter grazing by herbivores, protecting the plant
What are the groups of basidiomycetes?
Mushrooms Rusts Smuts and bunts Bracket fungi Puff balls and earth stars Jelly fungi Stinkhorns
Features of mushrooms
Basidiomycetes
Circular cap called a pileus
Supported by stalk called stipe
What is an agaric mushroom?
A type of fungal fruiting body characterised by the presence of a pileus that is clearly differentiated from the stipe, with lamellae on the underside of the pileus
What are rusts?
Basidiomycetes
Plant pathogenic fungi
Several spore forms
Often many types of host
What are smuts and bunts?
Basidiomycetes
Plant pathogens
Dark spores
Teliospores (thick-walled resting spores) formed in place of or inside developing seeds
What are bracket fungi?
Basidiomycetes
Usually growing out of standing timber
Stipe not always present
Indicate a heart rot in the tree
What are puff balls and earth stars?
Basidiomycetes Spores formed inside a chamber Released by pressure ‘shock’ e.g. rain splash Central cavity has sponge-like structure Produces billions of basidiospores
What are jelly fungi?
Basidiomycetes
Undifferentiated fruiting body
Sporulation (type of asexual reproduction) all over outer surfaces
What are stinkhorns?
Basidiomycetes
Smell of rotting flesh to attract carrion flies e.g. Phallus impudicus
Can grow through tarmac - very forceful
What is the specialisation of septa in basidiomycetes?
Septa have pore cap membranes surrounding the septal pore
Possesses dolipores - specialised dividing septal walls between cells with swellings by the septal pores
Features of basidiomycete nucleus
Nuclear envelope partially or totally dispersed
Dumbbell-shaped spindle-pole body
Astral microtubules
What is an example of a Basidiomycete species with over 30,000 mating types?
Coprinus cinereus
They are not compatible with their own mating type, but are compatible with any other mating type, meaning that there is a high chance that any spore meeting another will be compatible
What are clamp connections (form of fungal growth)?
Only occurs in dikaryotic fungi (cells with two genetically distinct but allelically compatible nuclei)
Ensures there is a copy of both of the genetically distinct nucleicin every cell
Formed by the terminal hypha during elongation. Clamp connection forms as each nucleus undergoes mitotic division. Septa separate each set of nuclei
Describe meiosis in basidia
- The two distinct nuclei fuse
- They then undergo meiosis, giving four nuclei
- One of each of these nuclei migrate into one of four spores, which are external to the basidium
- This is different to Ascomycetes, where the spores are internal to the ascus
What are the different types of gills in Basidiomycetes?
- Some have gills that are continuous with the stalk of the fruiting body
- Other have a thin veil which protects the gills during development, then breaks when they are complete, leaving a ring around the stalk and a grilled edge around the mushroom cap
What is an example of a basidomycete with a filament projecting the gills until the spores are ready to be released?
Agarius bisporus
What is a species of basidiomycete that has a universal wall which protects the whole mushroom (including the stalk and cap) until growth is complete, and an inner veil protecting the gills?
Amanita phalloides
What is a unique quality of basidiospores?
They are able to detect light and grow towards it
They are able to detect gravity and grow away from it - they can reoirientate themselves when grown on their side
Why is it so important that the cap is completely vertical in basidiomycetes?
If they are not completely vertical, tilted by as little as 5 degrees, 50% of spores can be lost as they will not be able to leave the gills
What do some basidiomycetes have instead of gills?
Pores or spikes with an equally large surface area
How do fungi acquire and digest nutrients?
- Nutrients acquired by absorption
- Nutrients must be small and soluble to be adsorbed
- Digestion occurs outside the body
- Enzymes secreted that digest polymers to give soluble products that can be absorbed
- They feed mainly on organic waste such as dead animal/plant matter
What are the three types of coloniser and how do they acquire nutrients?
- Primary coloniser - uses simple compounds. Short-lived organisms such as yeast, the initial fungi present when organic matter becomes available
- Secondary coloniser - can break down and absorb starches and proteins. They invest more in their environment and must secrete enzymes and wait to absorb the products
- Tertiary coloniser - use complex polymers such as lignin and cellulose (structural material in plants). They work very slowly as these polymers take a long time to break down
What animal products can fungi degrade?
Woollens
Leather
Bone
Gelatin
What plant materials can fungi degrade?
Cellulose and lignin
Many products including cotton, canvas, hemp, linen and timber
What types of rot can affect timber?
Soft/wet rots (high nitrogen levels required) Brown rot (breakdown of cellulose by hydrogen peroxide) White rot (bleaching of lignin as it is broken down Causes problems in construction, shipping and mining
What man-made products can fungi degrade?
Petrol/oil/diesel (fungus grows and divide between water and fuel)
Rubber (used in sewage pipe seals and air-tight seals on space stations)
Glass
Concrete/stonework
What are the methods of preventing food spoilage by fungi?
Drying Low humidity storage Cooling Reduced oxygen / increased CO2 Sterilisation by heat or UV Waxes to prevent entry of fungus Fungicides
How to prevent fungal disease outbreaks in plants
Quality controlled seed Hygiene Crop rotation Resistant varieties Chemicals
What does diseases can fungi cause in animals?
- Farmers lung: allergic reaction to inhaled spores
- Skin diseases: athlete’s foot, ringworm, candida
- Localised infection: fungi can infect puncture wounds and grow but remain localised due to the immune response
- Mycoses/systematic infection: spreading throughout the body
- White nose syndrome of bats: causes bats to awake during hibernation, reducing their fat reserves. If they wake up too many times, they will die
What fungus causes white nose syndrome of bats?
Geomyces destructans
How to control fungi
- It can be difficult to isolate and destroy eukaryotic cells within a eukaryotic host
- Differential toxicity: fungus has nkcwas to break down toxin so dies, whilst humans can survive toxin
- Unique pathways: drugs can be used to target pathways which are present in fungi but not in eukaryotic host
Common fungicides
- Benzimidazoles
- Strobilurins
- Carboxins
- Azoles
- Morpholines
- Echinocandins (inibit chitin synthesis)
How much is the production of Agaricus bisporus (common button mushroom) worth per year in the UK?
£350 million
Production process of mushrooms
- Straw and manure is composted by microbial fermentation then pasteurised
- The compost is ‘spawned’ using grain on which mycelia have developed, and the fungus is allowed to grow through the compost
- Capping: cover compost with peat/chalk mix to induce fruiting
- Requires controlled temperature and humidity
What is the other process of growing fungi and what are the costs and benefits?
‘Solid state fermentation’ - fungi grown in solid substrate
Variable and difficult to control but low-tech so inexpensive
Products of solid-state fermentation
- Breads
- Cheeses
- Soybean
- Rice
Bread production
- Saccharimyces cerevisiae (yeast) added to dough
- Aerobic restoration of free sugars in bread releases CO2, putting bubbles in the dough
- Limited enzyme secretion alters the proteins responsible for the texture of dough
- Yeast cells give additional flavour
- Too much salt or too low a temperature stops yeast from growing and gives hard flat bread
Cheese production
- The rind on cheese is fungal: the fungi begins digesting the cheese from the edge towards the centre
- The fungus secretes proteases which digest the casein, liquefying the cheese
- They also secrete lipases which alter the lipid profile of milk fats
- Fungi therefore alter the taste and texture of cheese
- In stilton and blue cheese, P. roquefortii grows within the cheese as veins and alters the cheese’s taste due to low oxygen levels
Other preserved products
Salami
Tempeh
Soy sauce
Sake and rice beers
Liquid-based fermentation
- Alcohol production by Saccharomyces cerevisiae: anaerobic fermentation of glucose to give ethanol
- Wines and ciders produced from natural sugars in ripe fruits
- Yeast cannot break down starch so cereals must be malted or mashed before fermentation can occur
Making Quorn:
- Mycoprotein is protein-rich food produced by fungi
- An air-lift fermenter uses air to create a flow around the vessel. The mixture is not stirred to maintain a better texture of hyphae
- The fermenter runs for 6-16 weeks
- The fungus is Fusarium venenatum
- The carbon source is corn steep liquor
- The nitrogen source is ammonium
- Potassium phosphate, magnesium sulphates, iron, calcium and sodium chloride also added
- Culture grown in lab, and allowed to grow until there is enough microbes to go in main fermenter. After 6-10 weeks, fresh medinis added and the fungus is harvested continually
What fungus causes sweating and stomach cramps in some people?
Agaricus xanthodermus (yellow-staining mushroom) Basidiomycete
What fungi causes hallucinations?
Psilocybe semilanceata (Liberty cap) Basidiomycete
What fungi can kill a human and how?
Amanita phalloides (Death cap) Produces alpha-amanitan and phalloidin, which are easily ingested. These cause nuclear RNA degradation in liver cells, preventing protein synthesis. Liver failure occurs within 10-14 days, mortality rate 50-90%
What are mycotoxins?
Fungally produced toxins Produced on cereals and oil-rich seeds Non-transmissible, seasonal Liver damage Carcinogenic
What fungi produces penicillin?
Penicillium notatum
What useful enzymes do fungi produce?
Amylases, glucanases and invertases - break starch into sugar Pectinases - clearing fruit juices Proteases - for washing powder Rennets - vegetarian cheese Hydrophobins - detergent additives Medical proteins - insulin, factor VIII
What was the first eukaryotic genome sequenced and what fungi was it?
1996
Yeast - Saccharomyces cerevisiae
