Page 2 Plant-Bacteria Interactions Edited by Iqbal Ahmad, John ...

Figure 7.1 LuxI/LuxR quorum-sensing system circuit of V. fisheri [17].
7.2 Acyl-HSL-Based Regulatory System: The Lux Systemj131
with a maximum intensity at 490 nm, accompanying the oxidation reaction has led
to this reaction being referred to as bioluminescence. Different luminescent bacteria
may exhibit differences in the luminescence spectrum and the color of the emitted
light due to differences in sensitizer proteins that cause shifts in wavelength [11].
While luxC–E encode products that form a multienzyme complex responsible for
the synthesis of the aldehyde substrate utilized by luciferase [12], luxG encodes a
probable flavin reductase [13] and is followed by a transcriptional termination site
[14]. The bioluminescence induction involves an interaction between OOHL and
the transcriptional regulator protein luxR. Once the autoinducer is bound to the
N-terminal regulatory domain, multimer formation by luxR is enhanced and the
C-terminal domain activates transcription from both the lux operons. The lux
regulon is subjected to a tight regulation. Expression of luxR is regulated by two