Have you ever wondered the tiny microbes living all around us talks? The answer is yess they do, find out how they do it and how they help each other in the overall growth and development. Its very interesting topic which includes how the bacterial community interacts with each other via quorum sensing. And also there are a few examples of microorganism and the way they carry out quorum sensing and how it helps them. i hope you all find my Presentation informative you can get in touch with me using my email if you are having any suggestions for this work i m kunj patel with best regards. My email is kunjpatel2122001@gmail.com

1. QUORUM SENSING IN GRAM
NEGATIVE BACTERIA
Kunj Patel

2. How do humans Interact?

3. Quorum Sensing
‘Quorum’ is a Latin word
meaning certain number
of members required to
carry out an activity.
Quorum sensing is a way
through which bacteria
communicate with each
other.

4. Quorum Sensing – The “Bacterial” Talk.
Cell-Cell communication mechanism
Density dependent
Produces Signaling molecules
Allteration in gene expression –group behaviour

6. QUORUM SENSING MOLECULES
• Autoinducer used by Gram (-) bacteria for intraspecies communication.
1: Acyl-homoserinelactones (AHLs)
• Autoinducer used by Gram (+) bacteria for intraspecies communication
2: Autoinducerpeptides (AIPs)
• Autoinducer used by many QS bacteria for interspecies communication
3: Autoinducer-2 (AI-2)

7. Quorum sensing
in Vibrio Fischeri
Vibrio Fischeri is a gram
negative bacteria which exist as
free living cells or as symbiot in
light producing organ of animal
host such as Hawaiian Bobtail
squid.
This bioluminescence with help
of Vibrio Fischeri helps squid
escape from predators and in turn
it gets nutrient rich environment.

9. How does it work?
1.PRODUCTION – auto-inducer molecule is produced
In case if vibrio fischeri it is N-(3-oxohexanoyl)-L-
homoserine lactone which is synthesized by LuxI gene
. (Acyl homoserine lactone or AHL)
2.RELEASE- autoinducer is released in surrounding
environment.

10. 3. DIFFUSION AND CHANGES IN GENE
REGULATION
In vibrio fischeri the autoinducer(AHL) directly diffuses in the cells by
AHL Receptors and binds to LuxR gene which is responsible for
expression of genes LuxCDABEG producing Enzymes required for
Bioluminescence.
When a critical level of AHL is reached gene regulation takes place and
the Autoinducer-LuxR complex activates the transcription for lux
operon and organism emits light.

12. Lux Operon

13. .
• The luciferase enzymes required for light production in V. fischeri are encoded by lux
CDABE, which exists as part of the lux ICDABE operon.
• Two regulatory proteins called LuxI and LuxR comprise the quorum sensing apparatus.
• LuxI: autoinducer synthase enzyme, and it acts in the production of an HSL, N-(3-
oxohexanoyl)-homoserine lactone.
• LuxR functions:
-To bind the autoinducer.
-To activate transcription of the lux ICDABE operon.
LUX OPERON

15. Two Component system

16. Quorum sensing in V.harveyi :
Vibrio harveyi---a free-living marine bacterium.
- It produces three distinct AIs to control bioluminescence,
biofilm formation, Type III Secretion (TTS), and
protease production.
The three V. harveyi AIs are:
1)HAI-1, an acyl homoserinelactone
2)AI-2, a furanosyl-borate-diester and
3)CAI-1.

17. Cont…..
• HAI-1 has only been shown to be produced by V. harveyi and its most
closely known relative, Vibrio parahaemolyticus, suggesting that HAI-
1 is an intraspecies signal.
• CAI-1 activity is produced predominantly by vibrios, suggesting it
could be an intra genera signal.
• AI-2 production is widely distributed in the bacterial world,
suggesting this is a relatively nonspecific, interspecies bacterial
communication molecule.

18. Quorum sensing in Vibrio harveyi.
-- The LuxM, LuxS and CqsA enzymes synthesize
the autoinducers harveyi autoinducer 1(HAI-1),
autoinducer 2 (AI-2) and cholerae autoinducer 1
(CAI-1), respectively.
These autoinducers are detected at the cell surface
by the LuxN, LuxQ and CqsS two-component
receptor proteins, respectively. Detection of AI-2 by
LuxQ requires the periplasmic protein LuxP.

20. (a) Low concentration
• In the absence of autoinducers, the receptors
autophosphorylate and transfer phosphate to LuxO via LuxU.
Phosphorylation activates
• LuxO, which together with s54 activates the production of five
small regulatory RNAs (sRNAs). These sRNAs, together with
the
• chaperone Hfq, destabilize the mRNA encoding the
transcriptional regulator LuxRVh. Therefore, in the absence of
autoinducers, the
• LuxRVh protein is not produced.

22. (b) High Concentration..
In the presence of high concentrations of the autoinducers, the
receptor proteins switch from kinases to phosphatases, which
result in dephosphorylation of LuxO.
Dephosphorylated LuxO is inactive and therefore, the sRNAs are
not formed and the transcriptional regulator LuxRVh is produced.

23. Why is quorum sensing required?
For organism it is
beneficial in
following ways
• Biofilm formation
• Virulance
• Acid tolerance
• bioluminecsence
• Competence development

24. For us…
For understanding pathogenicity of
bacterial species .
To understand the symbiosis of bacteria
within human body .
It helps in developing antibiotics

25. Keywords
-Bioluminescence
-interspecies and intraspecies
-Two component system
-biofilm
-symbiot.
-luciferase enzyme
-Transcription
- Gene regulation

26. Any Questions?

27. References
• Microbial Physiology 4th Edition by A.G Moat and J.W Foster .
• QUORUM SENSING IN BACTERIA by Melissa B. Miller and
Bonnie L. Bassler Department of Molecular Biology, Princeton
University, Princeton, New Jersey.
--Quorum sensing and quorum quenching in Vibrio harveyi:
lessons learned from in vivo work. Tom Defoirdt1,2, Nico Boon1,
Patrick Sorgeloos2, Willy Verstraete and Peter Bossier