Lecture 30 Flashcards
What are the two forms of motility in Myxobacteria? What do they have in common?
They are both forms of gliding motility (not flagellar motility).
S-motility (social):
- Groups of cells move together via twitching/rippling.
- They do this via type 4 pilli (T4P) - they send them out in the direction they want to go and then drag themselves there.
- The cells communicate with each other via contact.
A-motility (adventurous)
- Individual cells move via gliding motility
Explain how Myxobacteria use chemotaxis in their tactic behaviour.
The swarms can detect concentrations of nutreints, lipids, and prey cells via predataxis. This then results in rippling behaviour - period increases as the concentration of prey decreases.
Note that they do not have flagella!
As a point of comparison to Myxobacteria, how does chemotaxis in bacteria take place?
It involves the movement of the bacteria towards an attractant or away from a repellent. It occurs via a change in flagellar rotation direction. In E. Coli, counter clockwise rotation = “run”, clockwise = tumble
Under what circumstances do fruiting bodies form in myxobacteria? Describe how this process works.
A fruiting body is formed in response to starvation. The population collectively decides to enter starvation - this ellicits a stress response (the stringent response).
They will first stop growing, then come together to form a fruiting body. This is only possible if there are enough cells present - a certain quorum (cell density) must be met. If there are enough, the cells will pool their resources to form the fruiting body, and they will differentiate. Some will autolyse to provide their resources.
Some will also form myxospores, which allows for the dispersal of clones in other regions that might still have nutrients (since they are starving in their current location).
Where is the stringent response activated in myxobacteria? Describe how this works.
In the ribosome. When they are doing translation, mRNAs are read and tRNAs bring the amino acids. When cells are replete with nutrients, they continues freely. When cells are starving, there will be a slowdown in the loading of new amino acids attached to tRNA. tRNAs will not get charged with amino acids as quickly, so the rate of extension of the peptide chain will slow down.
There’s a protein, RelA, that will detect this slowdown in the ribosome. The activation of RelA triggers the stringent response.
Explain the effect of RelA in myxobacteria once triggered.
When it detects that the ribosome is no longer functioning, it will:
1. Synthesize pppGpp when cells are starving. Once a threshold concentration of pppGpp has been reached, the stringent response is triggered.
2. pppGpp will stimulate Myxobacteria genes asgABCDE to produce Signal A. It will also turn off certain genes involved in DNA replication.
3. If there are enough Myxobacteria present (quorum), Signal A will accumulate to a threshold level to trigger the next set of signals and, eventually, the fruiting body.
What is Signal A made of? How does it travel between cells?
It is a mixture of peptides and amino acids that is created after pppGpp activates genes asgABCDE.
It is a diffusable and membrane-permeable substance, so it can enter cells through the membrane.
What determines the concentration of Signal A in the Myxobacteria colony?
The population density.
What ultimately determines whether or not a fruiting body is formed in Myxobacteria?
The concentration of signal A, which is determined by the population density. A sufficient quorum-sensing signal (threshold) is required to enter starvation.
If the signal A threshold is met, what 4 events will take place in the Myxobacteria population?
- Aggregation
- Fruiting body formation
- Pooling of resources
- Conversion of vegetative cells into myxospores.
How long does it take for Myxobacteria to go from a starving population to a fruiting body with myxospores?
Around 24 hours.
During fruiting body formation, name 5 factors that must be monitored by Myxoabcteria.
- Cell density
- Timing and developmental events
- Tactic events (movement)
- Developmental autolysis and spore formation
- 3D spatial orientation
What is the purpose of a fruiting body (versus sporulation)?
The formation of a fruiting body allows for pooling of resources and raising of myxospores for better dispersion.
What is the equation dictating Myxobacteria autolysis and sporulation? Explain it.
Phospholipids —- (glucosamine + phospholipase) –> glycerol + AMI (fatty acids).
As the cells are starving and some are dying, there’s phospholipids being released that the other cells will eat. They get broken down by phospholipase into glycerol and fatty acids. The phospholipase is stimulated by glucosamine, which is from cell walls.
What are the two products of the Myxobacteria autolysis and sporulation reaction? What is the function of each?
Glycerol and AMI (fatty acids).
- Glycerol causes spore formation - contributes to the myxospore. Around 50% of the cells that do not autolyse become spores.
- AMI is the signal that causes 65-90% of cells to autolyse - it permeabilizes their membrane and then they pop. Their nutrients are used by the survivors.
