Transcript Slide 1

Bacterial Quorum Sensing
APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Jan. 2008, p. 437–445
Many species of bacteria use quorum sensing to
coordinate their gene expression according to the
local density of their population.
Quorum sensing was first observed in Vibrio fischeri, a
bioluminiscent bacterium that lives as a mutualistic
symbiont in the photophore (or light-producing organ)
of the Hawaiian bobtail squid.
When V. fischeri cells are free-living (or planktonic), the
autoinducer is at low concentration and thus cells do
not luminesce.
However, when they are highly concentrated in the
photophore (about 1011 cells/ml) transcription of
luciferase is induced, leading to bioluminescence.
acylhomoserine lactone
(acyl-HSL synthase)
synthesize
LuxI
3-oxohexanoyl-DL-homoserine lactones
(3OC6HSL)
LuxR
To stabilize the transcription factor
Results and Discussion
The modeling suggests:
(i) A threshold response results from positive feed
back on a single, noncooperatively bound
regulatory element (either a LuxR or LuxI
homolog)
(ii) Bistability results from either positive feedback
on two noncooperatively bound regulatory
elements or positive feedback on one or more
cooperatively bound regulatory elements
In Drosophila, temporal gradients of regulatory
proteins drive differential patterning of the embryo
by using , for example, bistability generated by
positive feedback on a signaling receptor
In mammalian cells, interferon molecules secreted
by virus-infected cells lead uninfected cells to upregulated antiviral defenses via interferonstimulated positive feedback.