Bacterial development Flashcards
Which functions can cells acquire through development?
Stress survival, Physiological specialisation, Cell dispersal, Symbiotic relationships
Why is Myxococcus a model organisation for investigating bacterial development?
One of the first bacteria to develop multicellularity. It has a very large genome (10Mb) with many regulatory and sensory systems which other bacteria do not have.
over 100 serine/threonine kinases (E. coli has none), 8 chemosensory systems (E. coli has none), 43 σ-factors.
Can form rafts, swarms, mounds, fruiting bodies etc
How does Myxoccocus behave in high nutrient conditions?
Forms swarming bodies of up to 1 million cells. They move and eat together and can also kill other bacteria.
How does Myxococcus behave in low nutrient conditions?
Aggregate into mounds and form a fruiting body. Cells in fruiting bodies differentiate into 3 different types of cells:
80% of cells undergo autolysis to supply nutrients to differentiating spore cells
15% of cells differentiate into spores which are highly resistant to heat, dessication, radiation and other conditions. Develop a thick carbohydrate coat and have a 2N geome.
5% of cells differentiate into periphery rods which act as scouts remaining vegetative but rarely dividing. If they sense high nutrient conditions they can reinitiate swarming.
What are the candidates for pheromones that stimulate the formation of fruiting bodies in Myxoccocus xanthus?
- C-signal, it is produced by cleaving CsgA, a short chain (227aa) alcohol dehydrogenase (C-signal is the terminal part). C-signal interacts with receptors on adjacent cells aligning them.
- SocA, has no homology to the C-signal, overexpression of SocA induces fruiting body formation in the absence of C-signal.
CsgA has homology to HSD10, a human developmental signal.
Describe kin recognition in Myxococcus
Many strains of Myxococcus can predate on other strains. They have evolved a defence mechanism to identify similar strains; Surface glycan receptors interact with surface protein TraA on adjacent cells. If the two adjacent cells express similar TraA alleles, e.g., they are the same/similar strain, the outer membranes can fuse allowing the exchange of genetic material and cellular components (like a repair).
If the alleles are different, there is no membrane fusion & they do not form fruiting bodies.
What are cyanobacteria and why are they useful for researching bacterial development?
Cyanobacteria are a diverse group of photosynthetic prokaryotes. They are gram negative photoautotrophs which show gliding motility without any flagella.
They show complex differentiation & have polymorphic cell cycles which are often nutritionally controlled, such as by the availability of nitrogen
What are Chroococacean cyanobacteria?
They are unicellular rods & cocci which are non-motile. They divide via binary fission
What are Pleurocapsalean cyanobacteria?
Unicellular but can form cell aggregates. Multiple fission of vegetative cells form Baeocytes a type of reproductive cell. (basically a load of spores in a thick capsule)
What are Oscillatorian cyanobacteria?
They form filaments called trichomes. Filaments can break up into groups of motile cells called hormogonia
What are Heterocystous cyanobacteria?
Trichomes which contain vegetative cells, heterocysts which fix atmospheric nitrogen into ammonium to supply vegetative cells and akinetes which are a type of resting cell formed in low nutrient conditions (anabaena species of heterocystous cyanobacteria).
Like Oscillatorian, filaments can break up and form hormogonia.
Tell me about heterocyst properties
Terminally differentiated cells, cannot divide; have a finite lifespan.
No calvin cycle, they can’t fix CO2; ferredoxin is supplied by adjacent vegetative cells. They fix atmospheric nitrogen to ammonium via nitrogenases which is exchanged for ferredoxin with neighbouring cells.
Thick envelope restricts O2 diffusion into heterocysts, important as nitrogenases are oxygen-sensitive.
Explain the process of heterocyst differentiation
- NtcA senses nitrogen deficiency as a ratio of 2-oxoglutarate:ammonium
- NtcA activates HetR, HetR is further activated by HetF
- HetR activates het gene transcription which induces heterocyst formation
- HetN and PatS are diffusable peptide signals inhibiting heterocyst formation in adjacent cells. PatS can not affect heterocysts.
