Flashcards in Lecture 9 Deck (14):
How might a bacterial communication system work?
- where does the signal come from
- type of molecule
- regulatory mechanism
- why would the population's gene expression shift at the same time?
Signal genes and transporter genes activate response genes, via various methods.
- Feedback regulation
- Two component system
- Quorum sensing
- Self-regulated positive feedback mechnanisms
In feedback regulation, where does the signal come from?
From the cells, so the signal becomes a measure of the number of cells and the density of cells.
In feedback regulation, how is the signal made?
Could be a product of the cell, made via an enzyme pathway within the cell.
How would the signal in a feedback regulation mechanism be exported from the cell?
Via carrier proteins in the cell membrane.
When lambda is moving toward lysogeny what does the repressor do?
It activates its own expression, pushing itself further toward the pathway producing it.
What is quorum sensing (QS)?
- 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.
What is a biofilm?
- A population of bacteria on an object that adhere and grow into a population that change gene expression as the population grows.
What is bioluminescence? eg) in Vibrio fischeri
- 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.
Luciferase bioluminescence gene expression is a positive regulatory mechanism:
- 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
What is the signal used in luciferase bioluminescence?
- acyl-homoserine lactone
- with a R group that varies between organisms
- lipid-like so they can diffuse across membranes
What are biofilms eg) Pseudomonas aeruginosa
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.
What quorum sensing mechanism does pseudomonas aeruginosa use for biofilm generation?
- 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
Two component feedback system eg) staphylococcus aureus
- 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.