Lecture 8 - Multicellularity and Social Behaviour

Question 1

How are multicellular activities coordinated in bacterial communities (Biofilms)?

Answer 1

Bacteria secrete signalling molecules to communicate with eachother in a process known as Quorum Sensing

Question 2

Why is Quorum Sensing Important to Bacteria (Give Examples)?

Answer 2

Enables coordination of their behaviour, allowing them to respond quickly to rapidly-changing environmental conditions e.g.,:
* Nutrient Availability
* Competition from other organisms
* Avoidance of toxic compounds

Question 3

Between what bacterial species does Quorum Sensing occur?

Answer 3

Quorum Sensing can occur both intra-species (within a species) and inter-species (between different species)

Question 4

Define Nanotubes

Answer 4

Tube-like connections that allow exchange of proteins and DNA (plasmids) within and between species

Question 5

Compare the Behaviour of (i) Undomesticated strains and (ii) domesticated strains of bacteria when growing on a surface (e.g., Petri Dish)

Answer 5

(i) Undomesticated strains spread across entire surface using swarming motility
(ii) Domesticated strains produce distinct colonies on surface

Question 6

Describe the process of the development of Swarming Motility

(4 Points)

Answer 6

1. Differentiation of Vegetative cells into specialised swarmer cells (filamentous, multinucleate)
2. Production of Flagella increases as result of contact of of cells with surface
3. Production of Surfactants occurs in response to cell population density signals
4. Rapid Migration across surface in multicellular rafts

Question 7

(i) What are Surfactants?

(ii) How are they produced?

Answer 7

(i) Lipopetides (e.g., Surfactin/srfA) secreted by bacterial cells that promote/assist swarming motility

(ii) Surfactin production is dependent on ComA, a TF that is activated (phosphorylated) by accumulation of ComX and CSF quorum-sensing signal peptides
* CSF gene expression - requires sigma factor H

Question 8

(i) What is Sigma H?

(ii) How is its expression regulated?

Answer 8

(i) Sigma factor involved in controlling expression genes involved in early stages of sporulation

(ii) Encoded by SigH, which is controlled by Spo0A due to it repressing AbrB, the repressor of SigH expression

Question 9

Describe Aerial Structures in terms of:
(i) Function
(ii) Structure (Give Example)

Answer 9

(i) Tree-like structures built by communities during later phases of sporulation, with cells at the top of the tree sporulating so that the wind carries spores away

(ii) Multicellular Aerial Structures supported by ECM e.g.,:
* B. Subtilis - ECM consists of Exopolysaccharides (Eps) and TasA (secreted EC protein), both of which are under the repression of SinR

Question 10

How does SinR regulate expression of TasA / Eps?

Answer 10

SinR competes with SinI for binding to operon, with this competition determining eps expression (SinR bound = inhibited expression)

Question 11

What are the two proposed mechanism by which yIbF and ymcA can promote aerial structure formation?

Answer 11

• yIbF and ymcA may:
  1. Act upstream of SinR and counteract SinR-mediated repression, either separately or as a heteromeric complex with SinI/SinR

2. Stimulate Synthesis/Stability of SinI

Question 12

How does Spo0A regulate expression of ECM required for Aerial Structure Formation?

(2 Points)

Answer 12

• Spo0A active (Spo0A-P) cells - SinI is expressed and counteracts SinR, relieving repression TasA and Eps
• Spo0A inactive cells - SinR represses formation of matrix, and indirectly favours vegetative state (division and motility)

Question 13

(i) Other than Swarming Motility, what other behaviours do bacteria display during very early sporulation?

(i) what does this involve?

Answer 13

• Fratricidal Behaviour is observed in genetically identical populations when nutrients are scarce, with toxins being used to kill siblings and release the nutrients they contain
• Cannibalism system - involves two independent gene clusters (both highly expressed at sporulation onset):
  1. Sporulating Killing Factor (SKF)
  2. Sporulation Delaying protein (SDP)

Question 14

(i) When do Bacteria secrete toxins?

(ii) Why does it only kill certain members of the population?

Answer 14

(i) During nutrient starvation, Spo0A is activated, which leads to inhibition of AbrB and subsequent activation of toxin-encoding genes

(ii) Spo0A inactive cells are killed by this toxin because AbrB inhibits the expression of sdpRI, which confers immunity to the SdpC toxin

Question 15

Why do Bacteria Secrete Toxins during Sporulation?

(3 Points)

Answer 15

1. Toxins kill Spo0A-inactive cells, which release nutrients that allow the cell to delay sporulation
2. Toxins may kill competitors, thereby promoting survival
3. Toxins may kill cells which are not genetically “fit” (i.e. are unable to enter sporulation)