L6 Social lives of bacteria

Question 1

Define supernatant

Answer 1

The liquid portion above a solid or sediment after centrifugation or settling.

Question 2

What are homoserine lactones?

Answer 2

They are produced and released by bacteria. As the population of bacteria increases, the concentration of HSL increases. When HSL levels reach a certain threshold, Quorum sensing is activated, which triggers a cascade that producing different things like virulence factors, biofilm formation, and adaptations to changes in the environment.

Question 3

Give 3 examples of homoserine lactones and say one thing about them.

Answer 3

1. 3-oxo-C6-HSL: produced by gram-pos bacteria (pseudomonas aeruginosa) involved in virulence factor regulation and biofilm formation.

2.3-oxo-C12-HSL: produced by Vibrio fischeri

3. C4-HSL: produced by bacteria. Involved in horizontal gene transfer regulation ie a defence mechanism against foreign DNA.

Question 4

What does homoserine lactone do?

Answer 4

It is an autoinducer of quorum sensing.

Question 5

Why is diffusion important in homoserine lactone?

Answer 5

As the number of bacteria increases in a population, they produce and release more HSL. The HSL diffuses away from the bacteria that produced and released, and binds to cell receptors in nearby bacteria. The increase in HSL concentration, activates QS when it reaches a certain level. The result of this is the triggering of the production of virulence factors, biofilm formation, and adaptions to environmental changes.

Question 6

What is the luxe gene locus?

Answer 6

A specific genetic region that contains the luxE gene.

Question 7

What is the luxCDABE operon?

Answer 7

A genetic unit found in bioluminescent bacteria i.e Vibrio fischeri. It consists of a cluster of genes that are involved in the production of bioluminescent machinery.

Question 8

What is a helix turn helix activator?

Answer 8

A type of DNA binding protein domain that plays a role in gene regulation.

Question 9

Tell me something about Homoserine Lactone synthesis

Answer 9

It is the production of HSL through specific enzymatic reactions in a bacterial cell. They are then released into the environment and diffuse away from the original cell to another cell nearby where they bind to receptors or proteins in the cell wall.

Question 10

What is meant by quorum sensing?

Answer 10

Coordinates how bacteria communicate within populations. It is triggered when HSL concentration reaches a particular threshold.

Question 11

What is quorum sensing control?

Answer 11

the regulation and coordination of gene expression and behaviour in bacteria through the process of quorum sensing.

Question 12

What is quorum sensing in gram positive bacteria, and why is it important?

Answer 12

Gram Negative has HSLs, Gram positive has AIP (Autoinducing peptides).

The mechanism is the same, and AIP also controls behaviours like production of virulence factors, and biofilm formation. It also produces sporulation (learn if you want, otherwise, allow it) and antibiotic production.

Question 13

What is quorum sensing in gram negative bacteria, and why is it important?

Answer 13

The production and release of HSL. t

Question 14

Name 3 key differences between gram positive and gram negative bacteria

Answer 14

GN has thinner peptidogylcan layer in cell wall. GP has thicker.

GN has lipopolysaccharides in their outer membrane. GP does not.

GN more resistant to antibiotics due to presence of outer membrane.

Question 15

What are Luxl/luxR homologues?

Answer 15

They are components of the quorum sensing system originally found in vibrio fischiri.

Question 16

How are virulence factors and quorum sensing important in the context of biofilm formation?

Answer 16

QS modulates the expression of virulence.

VF’s promote initial attachment to surfaces, facilitate the formation of micro-colonies, and contribute to structural integrity of biofilm.

Question 17

what is biofilm?

Answer 17

it is a structured community formed by bacteria after it adheres to a surface.

Question 18

Why is understanding biofilm important in medical microbiolgy?

Answer 18

They are associated with lots of infections, the bacteria in them is resistant to antibiotics, they can form on medical devices like feeding tubes, catheters, prosthetic devices, implants, prosthetic joints, IV tubes, breathing tubes etc.

Question 19

How is biofilm connected to MRSA in a clinical environment.

Answer 19

MRSA biofilms are highly resistant to antibiotics, they can enhance virulence of bacteria, can produce and secrete toxins and enzymes, and can persist on surfaces after initial treatment.

Question 20

What is the cyclic-di-GMP in biofilm formation?

Answer 20

A starvation signal (a type of stressor - there are others but the mechanism is not too dissimilar).

Question 21

Give two reasons why bacteria have a stress response.

Answer 21

A survival mechanism to get through food shortages, temperature fluctuations, environmental changes, to protect from damage.

Question 22

What is DSF in quorum sensing? (You dont need to know the name per se, but know a bit about what it is and what it does).

Answer 22

Unique to quorum sensing in bacteria of the Xanthomonadaceae family.

Question 23

What is the mechanism of quorum sensing in gram positive bacteria.

Answer 23

1. Bacterial population grows.
2. Bacteria produce and release HSL.
3. HSL diffuses away from bacteria that produced it.
4. As more bacteria produce and release HSL, HSL concentration increases.
5. HSL in other bacterial cells is detected by receptors or sensor proteins on cell surfaces that detect and bind to HSL’s - so they can plot together.
6. QS is activated when HSL’s reach a certain threshold which triggers a signalling cascade within bacteria.
7. Cascade = activation or repression of specific genes which can result in production of virulence factors, biofilm formation, and adaptions to environmental changes.