Here is a better description of "Quorom Sensing"
See link for full paper.
Given the complex interactions among
plant roots and mutualistic, commensal, and
pathogenic rhizosphere microbes, it follows
that the rhizosphere resounds with a cacophony
of chemical signals. Information is transmitted
by secretion of diverse compounds
mediating biofilm formation, infection of
roots, and modulation of plant immune
response pathways. Likewise, misinformation
is spread among competing populations of
bacteria, by pathogenic microbes interfering
with host defense signaling, and possibly
by plant roots to disrupt biofilm formation
or root colonization by harmful microbes.
(Barnard et al., 2007; Holtsmark et al., 2007;
Hu¨ ckelhoven, 2007; Morris and Monier, 2003;
Pieterse and Dicke, 2007; Ryan et al., 2008;
Somers et al., 2004; Vinale et al., 2008; Williams,
2007). Bacteria use quorum sensing (QS) to regulate
gene expression in response to their population
size.
Each member of the population
constitutively secretes a signaling molecule,
which builds up in the environment, eventually
reaches some threshold concentration, and
activates genes for such functions as bioluminescence,
virulence, or biofilm formation. A wide
variety of QS signaling molecules have been
described. These include peptides (generally
5-20 amino acids in length), acylhomoserine lactones
(AHLs), alkylquinolones, a group of furanones
referred to as autoinducer-2 (AI-2), and
diverse others (Chen et al., 2002; Williams,
2007). Some of these signals appear to be species-specific,
while some are sensed more generally,
allowing communication between bacterial
species. In fact, plants can recognize bacterial signals,
and thereby alter their gene expression
in response to the presence of specific species of
bacteria (Mathesius et al., 2003). Conversely, rhizosphere
bacteria respond to a variety of plantproduced
signals, such as salicylic acid (Yuan
et al., 2007), and it has been proposed that the
plant hormone, indole acetic acid (IAA), may act
as a QS signal in bacteria (Lambrecht et al.,
2000). Rhizobia show chemotactic responses to
nanomolar concentrations of legume-produced
phenolics (Somers et al., 2004). Furthermore,
many rhizosphere bacteria manufacture plant
hormones (Pieterse and Dicke, 2007; Ryan et al.,
2007), and some plants produce analogs of AHLs Au4
(Somers et al., 2004; Teplitski et al., 2000). Competing
bacterial species produce enzymes, such
as AHL-degrading lactonases, that degrade each
other’s QS signals (Somers et al., 2004). Despite
the number of published studies, the full extent
and complexity of communication among the
many inhabitants of the rhizosphere is still only
partially understood.
