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QUORUM SENSING IN LUMINESCENT BACTERIA
Paper : Marine microbial genomicsRoll no : MM-0914Name : Smruti Shivram Prabhudesai
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 .
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
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.
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
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.
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
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
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
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
MODEL OF QUORUM SENSING IN V. FISCHERI
REFRENCES
Waters C.M., Bassler B.L.,(2005). Quorum sensing : cell to cell
communication in bacteria. Annu. Rev. Cell Dev. Biol. 2005. 21:319–46
Popham D.L.,Stevens A.M.,(2006). Bacterial quorum sensing and
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