Micro - fungal growth and development

What is the basic unit of growth for fungi?

• The hypha

• Can form coenocytic/aseptate hyphae (no cross walls) or septate hyphae (cross walled)

How do septa in the hyphae affect flow of materials?

• Permit regulated flow of material

• Complete septa are imperforate

• Incomplete septa are perforate

• Simple perforate septa in ascomycota often contain a proteinaceous body - Woronin body

• Septa in basidiomycota are protected by a cap known as the parenthosome - septa are called dolipores

• Septa permit compartmentalisation of cells and differentiation

How is hyphal extension driven?

• Internal turgor pressure within the hypha

• Steady state or balanced lysis using the Vesicle Supply Centre (VSC) or Spitzenkorper

How do hyphal cells divide?

• No necessary quantitative or spatial relationship between the division of nuclei and cytoplasmic separation

• Hyphal cells grow and lengthen

• Nuclei divide

• New cell walls are formed within the hyphal compartment

What are different responses that can be exhibited by hyphae?

• Thigmotropic responses - touch sensitive

• Chemotropic responses - chemical sensitive

• Autotropic responses - responses to itself

• Galvanotropic responses - electrical field response

How can a mycelium be produced from individual hyphae?

• Hyphae can fuse (anastomose)

• Form a complex interconnected network - the fungal mycelium

What are different types of differentiated hyphae?

• Generative hyphae - hyphae that bear clamp connections or spores

• Skeletal hyphae - long, unbranched, thin or thick-walled hyphae

• Binding hyphae - thick-walled hyphae that branch frequently

• Fruitbodies with only generative hyphae are monomitic

• Fruitbodies with multiple types of hyphae are dimitic (two types) or trimitic (three types)

How do fungal cell walls protect the cell?

• Maintain the cell wall

• Stabilise internal osmotic conditions

• Protect against physical stress

• Scaffold for extracellular proteins and secreted enzymes

How does the mycelium grow?

• Exhibits growth phases

• Growth of the culture is followed by measuring biomass such as a growth pattern

• Shown to occur in the conventional sequence of growth phases

What are the growth phases exhibited by the fungal mycelium?

• Lag phase

• Exponential phase

• Linear phase

• Deceleration phase

How do mature mycelia show growth differently to young mycelia?

• Matured mycelia become affected by nutrient limitation, change in pH and growth inhibitors (metabolic waste products and secondary metabolites)

• Fungi show heterogenous growth patterns under resource unit restricted conditions

How does the fungal mycelium age?

• Different parts of the colony are at different physiological ages

• Youngest is actively extending hyphae at the edge of the colony

• Oldest is non-extending, sporulating mycelium at the centre

How do the Zygomycota reproduce?

• Utilise sexual reproduction

• Requires co-operative metabolism between + and - mating types

How do the Ascomycota reproduce?

• Filamentous Ascomycota mate with themselves to form sexual spores in ascomycetes

• Typical ascus contains 8 ascospores

How do the Basidiomycetes reproduce?

• Has thousands of sexes

• Homothallic - self fertile

• Heterothallic - sex requires a partner

• Monokaryon - uninucleate haploid (n)

• Homokaryon - uni- or multi-nucleate haploid (n)

• Dikaryon - binucleate haploid (n + n)

• Heterkaryon - multinucleate diploid (2n)

What are the different types of fungal breeding systems?

• Primary homothallism - mycelium is sexually self-fertile (clonal offspring)

• Heterothallism - mycelium is sexually self-fertile, requires another mycelium of another mating type

• Secondary homothallism - spores segregate both mating types together so mycelium is self-fertile

• Outcrossing - mating between different haploid strains

• Non-outcrossing - self mating between identical haploid strains

What are the different types of heterothallic breeding?

• Bipolar heterothallism - one mating-type gene with two alleles that are compatible but homogenic incompatibility

• Tetrapolar heterothallism - two mating-type genes with two (or more) alleles, only compatible combination is different at all 4 genes

What are the different types of outbreeding?

• Outbreeding - mating between different haploid strains from different spore sources

• Inbreeding - mating between different haploid strains from the same spore source