Bacteria use a process called quorum sensing to communicate with each other using chemical signal molecules called autoinducers. As the population density of bacteria increases, the concentration of autoinducers rises, allowing the bacteria to coordinate behaviors such as bioluminescence and biofilm formation. In the marine bacterium Vibrio fischeri, quorum sensing regulates genes that produce luciferase, the enzyme responsible for bioluminescence. LuxI synthesizes autoinducers that bind to LuxR, activating transcription of genes in the lux operon and producing light when the bacterial population is dense enough.

1. QUORUMSENSING IN LUMINESCENT
BACTERIA
Paper : Marine microbial genomics
Roll no : MM-0914
Name : Smruti Shivram Prabhudesai

2. WHAT IS QUORUM SENSING ?
 Quorum sensing is a mechanism of intercellular
communication within species of bacteria.
 Communicate with one another using chemical
signal molecules called as Autoinducer.
 It is a system of stimulae and response
correlated to population density.
 Quorum sensing process is unproductive when
undertaken by an individual bacterium acting
alone but becomes beneficial when carried out
simultaneously by large no of cells .

3.  Bacteria use quorum sensing to coordinate
certain behaviors such as biofilm formation,
virulence and antibiotic resistance based on
the local density of the bacterial population
http://www.independent.co.uk/www.photobiology.info

4. OCCURANCE
 Occur within a single bacterial species known as
Intraspecies Communication.
 or between different bacterial populations known as
Interspecies communication.
 or between bacteria and other organisms known as
Interkingdom Communication.

5. HISTORY
 The first such system
was described
inVibrio fischeri
(Nealson &
Hastings,1979), a
symbiotic species
that provides its
marine eukaryotic
hosts i.e., Squid with
light.
Euprymna scolopes

6. 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.

7.  The two genes which are essential for
regulatory scheme are
 Lux I gene: which encodes an autoinducer
synthase
 Lux R gene: which encodes an autoinducer
dependent activator of luminescence genes

8. MECHANISM
 Lux I gene synthesizes autoinducer (3-
oxohexanoyl-homoserinelactone)
 Autoinducer is produced continuously and it
diffuses across the cell membrane.
 Concentration of autoinducer rises
rapidlyand it binds to the Lux R protein and
causes the formation of an active dimer
molecule initiating transcription of Lux operon

9.  Lux R gene codes for protein called a
transcriptional activator
 Active Lux R - Autoinducer complex binds at
a site upstream from Lux operon
 RNA polymerase can bind to the LUX
promoter site and transcribe operon.
 Lux c lux D lux E are all involved in
production of substrate oxidised by the
enzyme luciferase in the production of light

10.  Lux A and Lux B are the two subunit of the
luciferase enzyme
 When this joins, the active luciferase enzyme
is completed and bioluminescence
commences

11. MODEL OF QUORUM SENSING IN V. FISCHERI

12. REFRENCES
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bioluminescence. Association for biology laboratory education 2005
.27:201-215
 Miller, M.B., Bassler B. L.(2001). Quorum sensing in bacteria. The
annual review microbiology 55:165-99
 Nealson K., Platt T., Hastings J.W. (1970) The cellular control of the
synthesis and activity of the bacterial luminescent system . Journal of
bacteriology 104:313-22
 Mc Lean R.C., Whitley M.,Stickler D.J. And claiborne W. (1997)
evidence of autoinducer activity in naturally occuring biofilms .FEMS
154:259 -263