Lecture 9

Question 1

How might a bacterial communication system work?
- where does the signal come from
- type of molecule
- detection
- regulatory mechanism
- why would the population’s gene expression shift at the same time?
(4)

Answer 1

Signal genes and transporter genes activate response genes, via various methods.

• Feedback regulation
• Two component system
• Quorum sensing
• Self-regulated positive feedback mechnanisms

Question 2

In feedback regulation, where does the signal come from?

Answer 2

From the cells, so the signal becomes a measure of the number of cells and the density of cells.

Question 3

In feedback regulation, how is the signal made?

Answer 3

Could be a product of the cell, made via an enzyme pathway within the cell.

Question 4

How would the signal in a feedback regulation mechanism be exported from the cell?

Answer 4

Via carrier proteins in the cell membrane.

Question 5

When lambda is moving toward lysogeny what does the repressor do?

Answer 5

It activates its own expression, pushing itself further toward the pathway producing it.

Question 6

What is quorum sensing (QS)?

2

Answer 6

• A form of density-dependent bacterial cel-cell communication mediating coordinated population-wide changes in gene expression.
• Associated with virulence, biofilm formation, sporulation, antibiotic production, bioluminescence.

Question 7

What is a biofilm?

Answer 7

• A population of bacteria on an object that adhere and grow into a population that change gene expression as the population grows.

Question 8

What is bioluminescence? eg) in Vibrio fischeri

Answer 8

• Vibria fischeri is a gram-negative marine bacterium
• They use ATP in the form of luciferase to form light.
• Often found in symbiosis with fish or squid, in order to find food, avoid predation, or find mates.

Question 9

Luciferase bioluminescence gene expression is a positive regulatory mechanism:

Answer 9

• luxR makes a signal that binds to a regulator, activating expression of luxl
• luciferase genes produce luciferase proteins which produce light
• luxl is a gene which makes an enzyme which makes a small MW signal that is exported from the cell

Question 10

What is the signal used in luciferase bioluminescence?

Answer 10

• acyl-homoserine lactone
• with a R group that varies between organisms
• lipid-like so they can diffuse across membranes

Question 11

What are biofilms eg) Pseudomonas aeruginosa

Answer 11

An opportunistic pathogen that attaches to plastics and metals (especially in a hospital setting) forming micro-colonies, and with quorum sensing mature into a biofilm community.

Question 12

What quorum sensing mechanism does pseudomonas aeruginosa use for biofilm generation?

Answer 12

• LasI produces a signal which binds to
• LasR the early infection genes regulator.
• The early infections genes produced bind to RhII which binds to
• RhIR, the late infection genes regulator

Question 13

Two component feedback system eg) staphylococcus aureus

Answer 13

• A gram-positive bacteria, with a gene encoding the inducer peptide.
• These peptides are transported out of the cell, circularising the ends of them (AIP + signal).
• The circularised peptides are more stable.
• A two component system causes a cascade of gene expression to be induced.

Question 14

Interspecies communication via quorum sensing uses:

Answer 14

• good for anti-microbial agent targets, use of an antagonist and an autoinducer.