Cell-Cell Communication and Development in Bacteria

Question 1

What are the four types of behaviours controlled by quorum sensing?

Answer 1

1) Bioluminescence in Vibrio fischeri (squid)
2) Biofilm formation
3) Conjugation
4) Virulence

Question 2

What is the name of the operon that regulates the bioluminescence in Vibrio fischeri?

Answer 2

The lux operon encodes genes for self-regulation and for the production of luminescent proteins.

Question 3

At what level is the lux operon normally expressed?

Answer 3

Low basal level

Question 4

Name two lux proteins that the lux operon produces?

Answer 4

Lux proteins (Lux I and Lux R)

Question 5

What is the name of the bacteria that uses quorum sensing for bioluminescence?

Answer 5

Vibrio fischeri

Question 6

What are autoinducers?

Answer 6

Autoinducers are signaling molecules that are produced in response to changes in cell-population density. As the density of quorum sensing bacterial cells increases so does the concentration of the autoinducer. … Autoinducers allow bacteria to communicate both within and between different species

Question 7

What are autoinducers?

Answer 7

signaling molecules that are produced in response to changes in cell-population density. Autoinducers allow bacteria to communicate both within and between different species

Question 8

What does the luxI gene produce in the lux operon in vibrio fischeri?

Answer 8

Autoinducer - acyl homoserine lactone

Question 9

What are AHL’s?

Answer 9

autoinducers known as acyl homoserine lactone molecules which are the primary quorum sensing signals used by Gram-negative bacteria

Question 10

What does the luxR gene produce in the lux operon in vibrio fischeri?

Answer 10

Regulatory molecule that binds to

Question 11

What synthesises the autoinducer (AHL) in quroum sensing of vibrio fishceri?

Answer 11

LuxI protein

Question 12

Describe the benefit existing between vibria fischeri and squid?

Answer 12

The host provides a safe, nutrient rich environment for the bacteria and in turn, the bacteria provide light. Although bioluminescence can be used for mating and other purposes, in E. scolopes it is used for counter illumination to avoid predation(camouflage on moonlit night)

Question 13

How is luciferase produced in the lux operon in vibrio fischeri?

Answer 13

Products of LuxB and luxA

Question 14

How is the expression of the target genes in the lux system induced?

Answer 14

AHL’s attach to the regulatory molecule produced by LuxR and initiates transcription by activating the regulatory protein (changing its confirmation). This enhances the expression of the target genes and thus more luxI and more autoinducer produce.

Question 15

How does luciferase aid in producing light for vibrio fischeri?

Answer 15

Catalyses a redox reaction that produces oxidised and reduced chemical products as well as blue-green light

Question 16

Why is the reaction that produces light only turned on when appropriate in vibrio fisheri?

Answer 16

Costs a lot of energy to run - only happens when appropriate such as when they are all crowded together

Question 17

What is the principle behind bioluminescence?

Answer 17

Bioluminescence - switching light genes on requires quorum to be present. Lives in water and can turn on lights when there’s other vibrio fischeri bacteria around them.

Question 18

What synthesises the AHL’s in quorum sensing (bioluminescence)?

Answer 18

LuxI family signal synthases

Question 19

What do the AHL’s interact with to initiate transcription of lux operon in vibria fischeri?

Answer 19

luxR homologues

Question 20

Describe in detail how vibrio fischeri turn on the light for squid?

Answer 20

By quorum sensing
reaches concentration - activation of lux genes
LuxI produces a protein and synthesises the autoinducer (acyl homoserine lactone). Lux R gene produces a regulatory protein that combines with AHL’s to change it’s confirmation and activate it. This initiates transcription and enhances the expression of the target genes and thus more luxI and more autoinducer produce.

Question 21

What are the different steps in biofilm formation?

Answer 21

1) Attachment

Question 22

What occurs in attachment stage of planktonic bacteria to substrate (biofilm formation)?

Answer 22

Specific environmental signal induces a genetic program in free living planktonic cells.
In response to signal, the planktonic bacteria attach to nearby surfaces by means of flagella, pillai, lipopollysaccharides or other surface appendages.
As cells enter biofilm formation, they no longer maintain flagella and instead move along surfaces using twitching motility that involves extension and retraction of specific type of pillas. Stop moving and firmly attach to surface.

Question 23

What occurs in the colonisation stage in biofilm formation?

Answer 23

More and more cells bind to surface and divide to form microcolonies and can begin to communicate with eachother by sending and receiving chemical signals (quorum sensing)
Chemical signal molecules are made and secreted by individual cells but once population reaches certain number, the chemical signal reaches a specific concentration that the cells can sense which triggers genetically regulated changes that cause cells to bind to substrate and eachother. This influences amount of extracellular matrix produced by cell

Question 24

What occurs during the growth and matrix production phase in biofilm formation?

Answer 24

Quorum sensing influences the amount of extracellular matrix produced by cell. Thick slimy material consists of polysaccharide polymers called Exopolysaccharides and entrapped inorganic and organic materials. The extracellular matrix protects the cells from damage from environmental assaults.

Question 25

How does quorum sensing serve the biofilm?

Answer 25

Increasing resistance of biofilms to antibiotics

Maturation of biofilm into 3d forms such as columns and streamers to form channels through which nutrients flow

Question 26

What controls biofilm detachment?

Answer 26

Quorum sensing system

Question 27

How can differerent stresses in bacterial biofilm be detrimental to antibiotics?

Answer 27

The architecture of biofilm plays an important role in protecting bacteria under physical, chemical, and biological stress. Antibiotics usually target a bacteria cell’s ability to grow, which means that a hibernating bacterium is exempt from attack.

Question 28

How can differerent stresses in bacterial biofilm be detrimental to antibiotics?

Answer 28

The architecture of biofilm plays an important role in protecting bacteria under physical, chemical, and biological stress - allow to go to dormant state. Antibiotics usually target a bacteria cell’s ability to grow, which means that a hibernating bacterium is exempt from attack.

Question 29

What is bioluminescence in bacteria?

Answer 29

How some bacteria (e.g. Aliivibrio fischeri) generate light.

Question 30

What is biofilm formation under quorum sensing?

Answer 30

The transition from a planktonic (free-swimming) to a community-based lifestyle within a matrix constructed from biomolecules is often guided by quorum sensing

Question 31

What is conjugation under quorum sensing?

Answer 31

DNA transfer from one bacterium to another is governed by quorum sensing in the Gram-positive organism Enterococcus.

Question 32

What is virulence behavior under quorum sensing?

Answer 32

The expression of a virulent phenotype by pathogenic bacteria may occur under the influence of quorum sensing molecules. This may occur when a large number of bacteria is needed to establish a successful infection.

Question 33

What is the conjugation of the pCF10 plasmid transfer in Enterococcus

Answer 33

Expression of a large set of gene products required for conjugative transfer of the antibiotic resistance plasmid pCF10 is controlled by cell-cell communication between plasmid-free recipient cells and plasmid-carrying donor cellsusing a peptide mating pheromone cCF10.

Question 34

Describe the principle behind conjugation and quorum sensing

Answer 34

plasmids that produce their conjugative systems responding to stimuli from small peptides, called pheromones or autoinducers. These small peptides frequently regulate cellular signaling processes according to the population density, a process denoted as quorum sensing (QS) - enables bacteria to sense information about the surrounding species composition and to adapt their expression profiles. This process encompasses the production, elease, and detection of autoinducers

Question 35

What are the autoinducers found in conjugation of pCF10 plasmid transfer in Enterococcus

Answer 35

oligopeptide pheromone cCf10

Question 36

Describe the process behind the conjugation of pCF10 plasmid transfer in Enterococcus

Answer 36

This transfer of plasmid is mediated by pheromone signalling between the two cell types.

Question 37

The transfer of plasmid pCF10 from donor cells to recipient cells is mediated by what?

Answer 37

Pheromone signalling between the two cell types
Recipient cells secrete chromosomally encoded peptide cCF10 which is internalized by donor cells and induces the expression of genes involved in the conjugative process - Asc10 or “aggregation substance” which mediates a stable interaction between the donor and recipient cells. Subsequent transfer of the pCF10 plasmid from donor cells to recipient cells occurs

Question 38

What cells secrete the peptide cCf10 in pCF10 plasmid transfer in Enterococcus

Answer 38

Recipient cells

Question 39

What induces the expression of genes involved in the conjugative process of pCF10 plasmid transfer in Enterococcus

Answer 39

cCf10 - induces expression of Asc10

Question 40

What is the purpose of the expression of Asc10 by cCf10?

Answer 40

Asc10 or “aggregation substances” mediates a stable interaction between the donor and recipient cells to alllow transfer of the pCF10 plasmid from donor cells to recipient cells occurs