botany microbiology

1. QUORUM SENSING IN BACTERIA
Submitted to - Submitted by -
Prof. H. K. Kehri Sameen Zaidi
Prof. A. Dikshit Vandana Kumari
M.Sc. III sem
2014 - 2015

2. WHAT IS QUORUM SENSING ?
• ‘Quorum’ is a Latin word.
• It means the number of members of a group
required to be present to transact business or
carry out an activity legally
• In this process bacteria communicate via secreted
signalling molecules called “autoinducers”, which
contribute to the regulation of the expression of
particular genes.

3. OCCURRENCE –
• Within a single bacterial
species as well as
between diverse species.
• In some local insects use
quorum sensing to
determine where to nest.

4. HISTORY OF QUORUM SENSING
• The first such system was
described in Vibrio
fischeri (Nealson
&Hastings, 1979), a
symbiotic species that
provides its marine
eukaryotic hosts i.e.,
Squid with light.
Euprymna scolopes

5. GENERAL MECHANISM
• Bacteria showing quorum sensing requires two things –
(1) Signalling molecules called autoinducers or
pheromones.
(2) A receptor that can specifically detect the signalling
molecule.

6. • When the inducer binds the receptor , it activates
transcription of certain genes, including those for
inducer synthesis.

7. QUORUM SENSING IN GRAM
NEGATIVE & GRAM POSITIVE
BACTERIA

8. • Quorum sensing in Gram-negative
bacteria - The language of LuxI and LuxR
genes.
• Quorum sensing in Gram- positive
bacteria – Peptide mediated quorum
sensing.

9. In Gram negative bacteria
• Autoinducer – AHL
or N-acyl
homoserne
lactones.
• It is synthesized by
a LuxI homologue
and a LuxR
homologue.

10. Example 1 - Quorum Sensing in Vibrio
fischeri – Bioluminescence.
• Bioluminescence is defined as the emission
of visible light from living organisms.
• Bacteria are the most numerous of the light
emitting life forms.
• One of the most widely studied bacteria is
Vibrio fischeri.

11. Quorum sensing in Vibrio fischeri at low and high cell density

12. Example 2 – Antibiotic Production in Erwinia
carotovora
• Barrie Bycroft, Paul Williams & George Salmond were
studying mutants of Erwenia caratovora that were unable
make carbapenem (CarR) antibiotics
• One class of mutants could not make antibiotics on their own
but could do so when cross fed by a second group of mutants.

14. IN GRAM POSITIVE BACTERIA
• Eg.- Bacillus subtulis & Streptococcus
pneumonia use quorum sensing to develop
bacterial competence.
• Autoinducer – peptide (oligopeptides).
• Secreted by – ABC transporter (ATP
binding cassette transporter

15. MECHANISM
• Peptide signal works by binding to a sensor protein “
histidine kinase “, located in the cell membrane of the
bacterium.
• Histidine kinase become activated .
• Activation of the histidine kinase leads to
phosphorylation of response- regulatory gene, and
interaction with another regulatory protein facilitates
transcriptional activation (for RNA III).

16. GENERAL MECHANISM OF QUORUM
SENSING IN GRAM POSITIVE BACTERIA

17. • RNA III affects the transcription or translation of
the target gene.
• Peptide used as autoinducer in Gram Positive
Quorum Sensing is secreted through ATP Binding
Cassette transporter(ABC).
• ABC transporter are transmembrane proteins that
utilises the energy of ATP binding & hydrolysis to
carry out certain biological processes.

18. Example- ComD/ComE competence system in
Streptococcus pneumoniae
• 5 genes have been implicated in the regulatory
circuit for competence development.
• Auto inducing peptide signal to develop the
competence state is called CSP (Competence
Stimulating Peptide). .
• ATP Binding Cassette transporter of ComAB
processes and secretes the competence
stimulating peptide in the extracellular region.

19. ComD/ComE competence exhibited by Streptococcus
pneumoniae

20. • ComD is a sensor kinase protein which detects
the accumulated CSP at higher cell density.
• Higher than the threshold levels of CSP induce
auto phosphorylation of ComD transferring the
phosphoryl group to the response regulator ComE.
• Phosphorylated ComE activates transcription of
comX gene.

21. WHY DO BACTERIA TALK TO EACH
OTHER? OR WHAT IS THE NEED OF
QUORUM SENSING ?
As environmental conditions often change rapidly,
bacteria need to respond quickly in order to
survive.
1) Quorum sensing enables bacteria to coordinate
their behaviour.
2) It is very important for pathogenic bacteria during
infection of a host to coordinate their virulence in
order to be able to establish a successful
infection.

25. EVOLUTION OF QUORUM SENSING SYSTEMS IN
BACTERIA HAVE BEEN ONE OF THE EARLY STEPS
IN THE DEVELOPMENT OF MULTICELLULARITY
• Although bacterial quorum sensing systems differ in
every case the ability to communicate with one another
allows bacteria to coordinate the gene expression &
therefore coordinate the behaviour of the entire
community
• Presumably this process bestows upon bacteria of the
qualities of higher organisms.
• Evolution of quorum sensing systems in bacteria
could therefore have been one of the early steps in the
development of multicellularity.

26. QUORUM SENSING INHIBITOR
• Efforts to disrupt biofilms have enabled the
identification of bioactive molecules produced by
prokaryotes and eukaryotes.
• These molecules act primarily by quenching the
QS system. The phenomenon is also known as
QUORUM QUENCHING .
• QS inhibitors are molecules that interrupt the
pathway of communication bacteria used to
regulate expression of virulence factors.

27. EXAMPLES
• N-Acyl homoserine lactonase, encoded by aaiiA,
attacks the lactone bond, causing ring opening
of AHLs.
• Transgenic plants harbouring the aiiA gene from
Bacillus thuringenesis were less prone to
maceration by Erwinia carotovora.
• Other bacteria including Arthrobacter sp,
Klebsiella pneumonia, Psedomonas sp.,
Variovorax sp.., etc., harbour enzymes capable of
AHL destruction.

28. • Best studied example of QS inhibition stems from
a marine alga – Delisea pulchra.
• It produce several halogenated furanone
compounds capable of interfering with AHL-
mediated signalling in bacteria.
• It prevent the AHL from binding to the luxR
homologues & eventually cause a rapid
turnover of these proteins.

29. • Manefield et al demonstrated the potential of the
halogenated furanones in preventing the pathogens
Vibrio harveyi from infecting the commercially
important black tiger Paneus mondon.

30. QUORUM SENSING IN SOCIAL INSECTS
1. ANTS - Colonies
of the
Temnothorax
albipennis nest in
small crevices
between rocks.
When the rock
shift & nest is
broken open, these
ants must quickly
chose a new nest to
move into

31. • HONEY BEES –
Apis mellifera also
use quorum sensing
to make decisions
about new sites

32. COMPUTING & ROBOTICS –
• Quorum sensing can also be used to coordinate the
behaviour of autonomous robot swarms.
• Using a process similar to that used by
Temnothorax ants , robots can make rapid group
decisions without the direction of a controller.

33. LIST OF VARIOUS RESEARCH INSTITUE
WORKING ON QUORUM SENSING
• University of Nottingham.
• Princeton university – Department of molecular
biology.
• J. Craig Venter Institute.
• Helmholtz Centre for Infection Research.
• National Institute of General Medical Sciences.

34. IN INDIA –
• Institute of Technology Bombay, Powai,
Mumbai.
• Institute of Technology, Chennai.
• Yenepoya Research Centre, Yenepoya
University, Mangalore.
• National Botanical Research Institute, Lucknow.

35. QUESTIONS
1) Define quorum sensing in bacteria ?
2) Name the bacteria in which quorum sensing was first
discovered and who discovered it.
3) Differentiate between Gram negative and Gram positive
bacteria with reference to quorum sensing only.
4) What are autoinducers ? Explain with reference to both
Gram negative & Gram positive bacteria.
5) How quorum sensing is beneficial to Euprymna
scolopes ?

36. 6) Give a detailed mechanism of quorum sensing in
Gram positive bacteria with reference to
competence in bacteria.
7) What is the full form of ABC ? What is the role of
ABC in quorum sensing?
8) Explain quorum quenching with example.
9) Write short note on quorum sensing in social insects.
10) List various research centres working on quorum
sensing.

37. REFERENCES
• Google.
• Life Sciences – Fundamentals & Practice , Part 1
By – Pranav Kumar & Usha Mina.
• Papers – Bacterial bioluminescence: its control and
ecological significance by Nealson K.H. , Hastings,
J.W.(1979).
• How bacteria talk to each other by quorum sensing
by Bonnie L. Bassler.

38. THANK YOU