Slide set 31

Question 1

Describe the tactic behaviour of myxobacteria?

Answer 1

Movement of flares

• Swarms of ells move toward colonies of other bacteria
  
  • But also toward inert objects
  • Therefore, this behaviour is NOT a chemotaxis
  • Attracted by perturbation in water kind of… Sense perturbation and go towards it

Chemotaxis
- Swarms of myxobacteria can detect concentrations of nutrients, lipids, and prey cells (predataxis)

• Detection of prey results in rippling behaviour
  - Rippling period inc’s as concentration of prey decreases
• Can detect prey aspects i.e. mucoid vs non-mucoid colonies, and respond differently depending upin what is detected

Question 2

Describe the fruiting body step in the lifecycle of myxobacteria

Answer 2

• Fruiting body is formed in response to starvation
  - Population collectively decides it is starving
  - Starvation elicits STRESS RESPONSE
• Individual myxobacterial cells then:
  - STOP GROWING
  - COME TOGETHER then cooperate to form a fruiting body
• Cell-cell communication (chemical and tactile)
• Cellular differentiation, some cells autolyse
• Resources are pooled to form fruiting body and myxospores
• Dispersal of myxospores allows clones to leave region that has been depleted of nutrients (since cells are starving)

Question 3

What is the starvation series of event in myxobacteria?

Answer 3

Starvation a.a. is sensed by ribosomes, activates the RelA enzyme, and thus triggers a series of events:

1. RelA synthesizes pppGgg (guanosine pentaphosphate) and/or ppGpp when cells are STARVING
   - Once treshold concentraiton of pppGpp is reached, indicating true starvation, the “stringent response” is triggered
2. pppGpp stimulates Myxobacteria cells to produce Singnal A
3. if Myxobacteria population is LARGE ENOUGH, Signal A will accumulate to a treshold level and then trigger the next set of signals (B,D,E,C) and responses and so on

Question 4

What is Signal A in myxobacteria?

Answer 4

Type of quorum sensing

• Produced by starving cells via the conversion of proteins into a mixture of peptides and a.a.
• Diffusable, MEMBRANE-PERMEABLE, detactable by all cells
• Concentration is relative to population density
• Quorum sensing singal that allows the population to make collective cell-density-dependant developmental decisions
  - via gene expression
• If population IS LARGE ENOUGH, quorum-sensing leads to:
  - Aggregation
  - Fruiting body formation
  - Pooling of resources
  
  • Conversion of vegetative cells into myxospores

Question 5

What happens if population is large enough and myxobacteria are starving?

Answer 5

• Aggregation
• Fruiting body formation
• Pooling of resources
• Conversion of vegetative cells into myxospores

Question 6

What are the steps in fruiting body formation? What must cells MONITOR?

Answer 6

Must monitor:

• Cell density
• Timing and developmental events
• Tactic events (movement)
• Developmental autolysis, spore formation
• 3D spatial orientation

Question 7

Why are myxobacteria making fruiting bodies? why don’t they just sporulate?

Answer 7

Because fruiting bodyallws for pooling of resources and raising myxospores for better dispersion

Question 8

How do myxobacteria control autolysis and sporulation?

Answer 8

• Glucosamine (cell wall component) stimulates the enzyme PHOSPHOLIPASE to degrade phospholipids into 2 fractions:
  - AMI ( a mixture of F.A.)
  - Glyceril
• AMI is the AUTOLYSIS SIGNAL
  - Stimulates 65-90% of the cells to lyse
  - Released nutrients utilized by the survivors
• 50% of the survivors sporulate
• Sporulation can be artificially-induced by glycerol
  - Glycerol stimulates peptidoglycan break-down in vitro
  
  • Not entirely clear how it is induced in nature …
• Myxospores have a though “Shell”
  - Resist lack of nutrients and harsh conditions
  
  • Survive many years but germination not well understood