Fungi Flashcards
classification
eukaryotes - opisthokonta ‘cells propelled by a single posterior flagella’ although it’s been lost in fungi
name 2 things only recently eliminated from fungi
the slime moulds and oomycetes, traditionally placed in the fungi, are in completely different groups and have only recently (2010!) been eliminated from fungi. Still v controversial among mycologists
fungal phyla
basidiomycota ascomycota glomeromycota zygomycota chytridomycota
IN THAT ORDER
which phyla haven’t moved about
basidiomycota
ascomycota
what are fungi?
• Eukaryotic
• Typically haploid nuclei
▪ They are true diploids but spend most of their time in haploid state
• Reproduce mainly with sexual and asexual spores
• Rigid cell walls with chitin
• Mostly filamentous (hyphal) growth form
• Heterotrophic
▪ All require preformed organic material
▪ There are no known photosynthetic fungi!!!!!
fungal cell wall
mannoproteins B-1,6-glucans and B-1,3-glucans CHITIN (makes it rigid) phospholipid bilyaer of cell membrane
function of fungal cell wall
Functions: • Determines shape • Provides protection • Site of nutrient exchange • Allows system to be pressurised via turgor (osmotic pressure)
what are fungal hyphae?
- Hollow tube containing cytoplasm
- Has a rigid wall
- Lots of CYTOPLASMIC STREAMING which move at quite high rates (allow mixing and transport of contents)
- May be compartmentalised with SEPTA, which roughly divide the tube into different sections
- Growth occurs at the tip and branch points (vesicles!)
- Typical eukaryote with nucleus in membrane, ER, mitochondria, golgi etc.
Model of apical hyphal growth
Model of apical hyphal growth
• Vesicles containing lytic enzymes fuse with the membrane about 10μm from the tip
• Enzymes break down some of the wall polymers – local weakening
→ There is a constant balancing act between stability and chaos
→ The enzymes want to dissolve the wall enough to weaken it without deforming too much so that it fails
• High turgor pressure in the hyphae causes weakened viscoelastic wall to stretch
• Vesicles containing new wall precursors fuse and new material is synthesised
→ The cytoplasmic stream is essential to transport material for forming a new cell wall from far away
• Hyphae re-hardens and tip has moved forwards
Complex 3D hyphal networks
- form by
- gives rise to
These form by…
• apical tip growth and branching
- The extent of branching dep. on the species and the nutritional status of the environment
• hyphal fusion (anastomosis)
- Fusion allows remodulation of transport system. Can do so in optimal fashion
This gives rise to…
• Radially symmetrical colonies on rich media
- Hyphal fusion can remodel these radial colonies
Function of septa
Provides mechanical strength
Mechanism for isolating damaged or ageing hyphal lengths
Allows differentiation e.g. during sporulation
Not all fungi have them!
- zygomycetes don’t, asco and basidio do
hyphae colonies
- diff between inner and outer regions
- regulation of whole colony growth under diff environmental conditions
Inner region = denser, fused hyphae
- Positive autotrophy and anastomosis give good connectivity for transport
Outer region = sparser, unbranched hyphae
- Exploratory hyphae
- Negative autotropy giving good space-filling
• Branching frequency is sensitive to environmental conditions.
- Under nutrient excess, there are more exploratory hyphae (fungal foraging) and there are more dense colonies
Autotropism –
sensing of neighbouring hyphae via O2 or CO2 concentrations followed by growth towards (+ve) or away (-ve) from neighbours
Do zygomytes have septa?
- Normally aseptate, allowing unrestricted cytoplasmic streaming.
- But sometimes form septate to allow isolation
Do Ascomycetes have septa?
Ascomycetes – Woronin body
- Woronin bodies clog septal pores
- Open form allows cytoplasmic streaming and nuclear and major organelle movement
- Closed form provides isolation if compartment damaged
Do Basidiomycetes have septa?
Basidiomycetes – Dolipore septum (looks like a stomata)
- Allows cytoplasmic streaming but restricts nuclear and major organelle movement
- Extent of regulation depends on degree of swelling, which regulates aperture
- Fully swollen form of dolipore septum provides isolation
How big are fungi?
• Microscopic hyphae: 1-10μm in diameter • Macroscopic mycelium: ‘dark honey fungus’ is the largest living organism. - Plant pathogen - It covers an area of 10km - Estimated weight ~20,000kg
What are the two types of fungal growth forms?
filamentous
unicellular division
- budding in yeast
- fission in yeast
Some species are dimorphic – filamentous or unicellular depending on environment
unicellular division
Budding in yeast
- Saccharomyces cerevisiae
- Vegetative cell develops bud, which detaches to form daughter cell
unicellular division
Fission in yeast
- Saccharomyces pombe
- Division is as is in bacteria
- Septum forms in vegetative cell, forming two identical daughter cells
how do fungi get nutrition?
SAPROTROPHIC NUTRITION
- secrete extracellular enzymes and then absorb via diffusion
• Using cell surfaces to absorb nutrients imposes a SA:Vol ratio constraint
→ Forces fungal hyphae to be microscopic in size like bacteria
→ Restricts hyphal diameter but not hyphal length, as we know from Armillaria ostoyae
• Extracellular enzymes released mostly from tip eg. Cellulases, lactases, proteases
Cellulose, lignin, protein are enzymatically depolymerised to simple sigars/a.as etc and absorbed through cell wall and membrane
Do fungi have cells?
• Hard to define fungal cells or their ‘basic unit’
- Septal compartment? – works for ascomycetes and basidiomycetes but many fungi are aseptate
- Hyphal growth unit? – ie. The smallest unit that can regenerate
fungal diversity - how many are there?
• 70,000-100,000 named species so far
• ~1000 new species named every year
• Recent estimates of diversity: 1.5-5.1 million species of fungi in the biosphere
- Only a v small % fungal diversity has been discovered
• They’re very abundant - per m2, length of fungi could wrap round the planet twice
When did fungi evolve?
• There is weak evidence that they were around ~1billion years ago (after higher algae, before the first fossils)
First fossils 400mya in devonian
Fossil fungi support that fungi co-evolved with early vascular plants
