Quorum Sensing

density and to connect cell population density with gene

expression. As part of their normal metabolic activities, bacteria

produce several small diffusible signaling molecules. These signal

molecules often positively regulate their own synthesis and were

originally described as autoinducers (AI). The best known QS

systems are based on the signal moleculesN-acyl homoserine lac-

tones (AHLs), of whichN-3-oxo-hexanoyl homoserine lactone (3-

o-C6 HSL) represents the signal associated withV. fischeri[6].

AHLs represent the first class of AI to be described [7]. The

genes associated with the production of these signals include an

AHL synthase and an AHL-binding transcriptional regulator. InV.

fischerithese genes areluxIandluxR, respectively [8]. Similar genes

in other Gram-negative organisms having AHL-regulated QS are

luxIandluxRhomologues even though the QS-mediated gene

functions in these organisms do not involve bacterial luminescence

[7]. Table1 shows a list of representative AHLs.

Other representative AHLs include the N-butyryl HSL

(C4-HSL) andN-3-oxo-dodecanoyl HSL (3-o-C12 HSL), both

Table 1
Commonly used bioassay strains

Strain Use Reference

Agrobacterium tumefaciens

A136 (pCF218)(pCF372) Detection of broad range of AHLs [29, 35]

(also referred to as WCF47(pCF218)

(pCF372))

(3-o-C4 to 3-o-C12 HSLs, C5 to C10 HSLs)a, b

NTL4 (pCF218)(pCF372) Detection of broad range of AHLs [36, 37]

(3-o-C4 to 3-o-C12 HSLs, C5 to C10 HSLs)a, b

KYC55 (pJZ372)(pJZ384)

(pJZ410)

Detection of broad range of AHLs [30]

(3-o-C4 to 3-o-C18 HSLs, C4-C18 HSLs)a, c

KYC6 (pCF218)(traM-tn5-gusA,

KmR)

3-o-C8 HSL overproducer, positive control for

bioassay

[51]

Chromobacterium violaceum

ATCC 12472 wt, used in quorum signal inhibition screens, indirect

AHL detection

[11, 33]

ATCC 31532 C6 HSL overproducer, used as positive control for

CVO26 bioassay

[11]

CVO26 Detection of C4- and C6-HSLs [11]
aFor details,see[30, 35]. All strains grow at 30C
bFor plasmid maintenance, grow on LB + spectinomycin (50μg/ml) and tetracycline (4.5μg/ml)
cFor plasmid maintenance, grow on LB + spectinomycin (50μg/ml), tetracycline (4.5μg/ml), and gentamycin

(15μg/ml)

4 Starla G. Thornhill and Robert J.C. McLean