Module 6: Reg. of Gene Expression (Quorum Sensing) Flashcards
Quorum Sensing
A chemical signaling system that allows for detection of the PRESENCE and NUMBER of microbes in the environment
Quorum sensing leads to the regulation of what kind of genes?
Density dependent genes!
“Quorum” refers to…
“The number of members of a group that needs to be present in order to conduct business”
In bacteria, what does it mean to “achieve quorum”?
Means that enough cells are present to accomplish a task that individual cells cannot do alone
Quorum sensing involves the release of…
Release of autoinducers into the environment by bacterial cells
Autoinducers
Specific signaling molecules used in quorum sensing that increase in concentration as density of a population increases
What is the relationship between population density and autoinducer concentration?
As population density increases, autoinducer concentration increases
(and same for decreases)
–> They change WITH each other!
How can bacterial cells assess their population density?
WHY?
By detecting autoinducer concentration in their surrounding environment
–> Works because of the relationship between autoinducer concentration and population density!
As detected population density changes, what is likely to occur in the detecting cell?
Change in gene expression!
Quorum sensing specificity
–> What does it depend on?
Communication via quorum sensing CAN BE specific!
–> Different populations use different autoinducers for signaling so molecules that can be detected by one population may not be detectable by another == specificity
What is a prototypical quorum signaling example?
The LUX system within Aliivibrio fischeri
What is special about Aliivibrio fischeri?
This bacterium has a lux system
The lux system was one of the…
FIRST quorum sensing systems to be characterized!
A. fischeri can exist in one of two states:
1) Free-living in the marine environment
2) As a symbiont in the light organ of the Hawaiian Bobtail Squid
In what state can A. fischeri produce light?
In its symbiont state
–> Living within the light organ of the bobtail squid
Why does A. fischeri produce light in its symbiont state but not when it’s free living?
Possibly because when in the light organ, high cell density is achieved (which is needed for lux)
Whereas in free living, the cells are dispersed within the marine environment and don’t have a high enough cell density to produce light
How can A. fischeri be MADE to produce light outside of the bobtail squid light organ?
One of two ways by culture:
1) By plating on agar in HIGH cell densities (mimics the densities found in the light organ)
2) By plating on agar with LOW cell densities and ADDING sufficient amount of AHL
The regulation of light production depends on the production of what?
What type of system regulates this?
Light production depends on the production of LUCIFERASE
–> Quorum sensing system regulates this production
What does AHL stand for?
N-acyl-homoserine lactone
What is AHL?
An autoinducer with the ability to induce luminescence
–> the autoinducer of the lux system in A. fischeri
Other than A. fischeri, where is AHL used and for what?
Used by a # of other members of the PROTEOBACTERIUM phylum for intercellular signalling
What is the structure of AHL?
A lactone (ester in a 5 member ring) substituent of the nitro group on an AMIDE
What differentiates AHL molecules in different organisms and pathways?
Why is this important?
The 1) Length and 2) Chemical modifications of the amide R side chain differentiates between AHL molecules
–> Important for signaling specificity
What type of bacteria do not use AHLs?
Gram (+) Bacteria