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

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