Quorum Sensing Videos with Bonnie Bassler

We found this extremely helpful video explaining quorum sensing and its implications on the scientific community: http://www.youtube.com/watch?v=azq6P0he2Xg

We also found a talk given by Bonnie Bassler that helped us in our understanding of quorum sensing.  She explains how it works in a very simplified manner.  Here are the links:  http://www.youtube.com/watch?v=nw2os1s0Hjw&feature=related and http://www.youtube.com/watch?v=ruP_Ap7DhwQ&feature=relmfu

She is extremely knowledgeable about quorum sensing!!

Quorum Sensing with Auto Inducer 2

1. Auto Inducer 2 (AI2) is formed by recylcing the molecule S-adenosylmethionine in the adenyl methyl cycle until 4, 5-dihydroxy-2, 3-pentanedione (DPD) is produced.
2. 4, 5-dihydroxy-2, 3-pentanedione (DPD) is then converted into one of two forms via hydration.
3. AI2 passively diffuses through the membrane.
4. The Lsr transporter brings AI2 into the cell.
5. AI2 is phosphorylated by LsrK.
6. The AI2-phosphate binds to LsrR and causes it to release DNA which decreases transcription of the Lsr gene.

Sources:
Image: http://www.grin.com/en/doc/264621/biological-nanofactories-altering-cellular-response-via-localized-synthesis

Quorum Sensing in Gram Positive Bacteria

1. Oligopeptides are cleaved into small functional units and secreted out of the bacterium through a transporter protein.
2. Signal oligopeptides are detected by a sensor protein on the bacterium's surface when they reach a significant concentration.
3. The protein becomes phosphorylated and the phosphate is transferred to a response regulator protein.
4. The phosphorylated regulator protein binds to a specific DNA site and alters transcription in the target gene.

An interactive video may be found here: http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::500::500::/sites/dl/free/0073375225/594358/QuorumSensing.swf::Quorum%20Sensing

(Gram positive quorum sensing may be found approximately halfway through the video)

Sources:

Image: http://www.sciencedirect.com/science/article/pii/S1369527499000259

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::500::500::/sites/dl/free/0073375225/594358/QuorumSensing.swf::Quorum%20Sensing

Quorum Sensing in Gram Negative Bacteria

1. Acyl homoserine lactoses are synthesized by enzymes and move through the bacterium membrane via passive diffusion.
2. When a significant concentration of lactoses is reached, it binds and activates a regulatory protein on the cell membrane.
3. The regulatory protein then binds to a specific DNA site and influences the target gene. It also induces more production of the lactose signaling molecules.

An interactive video may be found here: http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::500::500::/sites/dl/free/0073375225/594358/QuorumSensing.swf::Quorum%20Sensing

(Gram negative quorum sensing may be found approximately a third of the way through the video)

Sources:

Image: http://www.sciencedirect.com/science/article/pii/S1369527499000259

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::500::500::/sites/dl/free/0073375225/594358/QuorumSensing.swf::Quorum%20Sensing

Quorum Sensing Molecules

The concentration of the low weight extracellular molecules which facilitate quorum sensing is proportional to the size of the bacterial population. A small population produces a low concentration of sensing molecules, while a large population produces a high concentration of sensing molecules. These molecules are responsible for information exchange and inducing gene expression among bacterial populations.



Acyl homoserine lactones are present mainly in Gram negative bacteria and are in control of their own synthesis. There is a lot of diversity in this group, with different bacteria species being able to produce unique lactones; however, some bacteria species produce the same lactones. The head group consists of the homoserine lactone and is conserved among all types of lactones; the tail goup is the acyl function group and is a variable region that determines the specificity of the receptor.





Oligopeptide molecules are present mainly in Gram positive bacteria. Their synthesis is dependent on ribosomes and their peptides can be modified.




Pseudomonas quinolone signal is a quorum sensing molecule specific to the Psuedomonas species. High concentrations of these molecules are produced. They are transported via membrane vesicles.




Auto inducer two is a quorum sensing molecule used by many Gram negative bacteria to facilitate communication between different species.








Image sources:
Oligopeptide and Auto inducer two: http://www.grin.com/en/doc/264621/biological-nanofactories-altering-cellular-response-via-localized-synthesis
Psuedomonas quinolone signal: http://www.sciencedirect.com/science/article/pii/S0968000411001605

Helpful Articles

We have found a few articles that are extremely informative.  It will take us a few days to read through this information and figure out what pieces we can utilize, but read up! This is exciting!

ftp://www.daba.lv/grozs/Mikrobiologijas/BiotehIII/Kvorums/Genu_ep_kvor.pdf

http://www.sciencedirect.com/science/article/pii/S0092867402007493

Quorum Sensing Overview

Quorum Sensing is a type of communication in bacteria that is used to recognize self and induce specific gene expression in contained bacterial populations. This is done by producing various sensing molecules, which can influence or induce a change in phenotype for the entire population.  Bacterial populations can communicate about population size, metabolic state, or producing an end product such as bioluminescence. Quorum sensing is apparent in both single species populations and mixed species populations.  It can be used as a decision-making tool is the individuals have the capability to assess the number of other components they interact with and have a standard response once a threshold number of individuals is reached.

There are many examples of quorum sensing now known in the bacterial world, but the best known is Vibrio fischeri which is a bioluminescent bacteria.  When this bacteria is free-living and the auto-inducer is at high concentrations, the transcription of luciferase is induced causing bioluminescence.

Recent research into quorum sensing is working with antibiotics to target bacteria's ability to communicate with one another.  If the communication is interrupted, the bacteria do not have the ability to replicate to high enough levels to become pathogenic within a host and offer a chance for the host immune system to fight off the remainder bacteria.

There are three mechanisms in which bacteria conduct quorum sensing.  We are still attempting to understand these mechanisms and will post about them later.