Quorum sensing in bacteria.

17 Aug 2001 12:48 AR AR135-07.tex AR135-07.SGM ARv2(2001/05/10) P1: GDL
Annu. Rev. Microbiol. 2001. 55:165–99
Copyright c 2001 by Annual Reviews. All rights reserved
QUORUM SENSING IN BACTERIA
Melissa B. Miller and Bonnie L. Bassler
Department of Molecular Biology, Princeton University, Princeton, New Jersey
08544-1014; e-mail: mmiller@molbio.princeton.edu, bbassler@molbio.princeton.edu
Key Words autoinducer, homoserine lactone, two-component system, cell-cell
communication, virulence
s Abstract Quorum sensing is the regulation of gene expression in response
to ?uctuations in cell-population density. Quorum sensing bacteria produce and
release chemical signal molecules called autoinducers that increase in concentration
as a function of cell density. The detection of a minimal threshold stimulatory con-
centration of an autoinducer leads to an alteration in gene expression. Gram-positive
and Gram-negative bacteria use quorumsensing communication circuits to regulate a
diverse array of physiological activities. These processes include symbiosis, virulence,
competence, conjugation, antibiotic production, motility, sporulation, and bio?lmfor-
mation. In general, Gram-negative bacteria use acylated homoserine lactones as au-
toinducers, and Gram-positive bacteria use processed oligo-peptides to communicate.
Recent advances in the ?eld indicate that cell-cell communication via autoinducers
occurs bothwithinandbetweenbacterial species. Furthermore, there is mounting data
suggesting that bacterial autoinducers elicit speci?c responses from host organisms.
Althoughthe nature of the chemical signals, the signal relay mechanisms, andthe target
genes controlledby bacterial quorumsensing systems differ, inevery case the ability to
communicate with one anotherallows bacteria to coordinate the gene expression, and
therefore the behavior, of the entire community. Presumably, this process bestows upon
bacteriasome of the qualities of higherorganisms. The evolutionof quorumsensingsys-
tems inbacteriacould, therefore, have beenone of the early steps inthe development of
multicellularity.
CONTENTS
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
GRAM-NEGATIVEBACTERIA: LUXI/LUXR-TYPEQUORUM
SENSING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
The Vibrio ?scheri LuxI/LuxRBioluminescence System . . . . . . . . . . . . . . . . . . . . . 167
The Pseudomonas aeruginosa LasI/LasR-RhlI/RhlRVirulence System . . . . . . . . . 168
The Agrobacterium tumefaciens TraI/TraR Virulence System . . . . . . . . . . . . . . . . . 171
The Erwinia carotovora ExpI/ExpR-CarI/CarRVirulence/Antibiotic
System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
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