Quorum Sensing

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based on AHL synthesis (i.e.,luxI-directed inhibition) or AHL
regulation (i.e.,luxR-directed inhibition) is shown in Fig.2 and
examples of quorum inhibition usingC. violaceumare shown in
Fig.3.A. tumefaciensandC. violaceumbiosensors are compared in
Figs.4 and 5.
Here we describe several approaches in whichA. tumefaciens
andC. violaceumcan be used for QS detection. The first section
describes extraction and concentration of AHLs using an ethyl
acetate protocol [35, 38]. Chemical extraction is not required but
can increase the sensitivity of bioassays and also provides material
for downstream applications, including the detection of individual
AHLs from environmental samples. The second section describes
theA. tumefaciensbioassays, which are generally used for detecting
C6-C12 HSLs, although C14-C18 HSLs have been detected at


Fig. 1Cross-feeding plate assays for AHL detection. (a) shows indicator strain
C. violaceumCVO26 producing violacein in response toC. violaceum 31532
(C6-HSL overproducer, positive control) andC. violaceumATCC12472 (wt) (a)
[11, 33]. No violacein is produced when strain CVO26 (cviImutant) is streaked
against itself (b). TheA. tumefaciensplate assay is shown in (c) and (d). (c)A.
tumefaciens A136 (PCF218)(PCF372) (bioassay strain) expressing lacZ in
response toA. tumefaciensKYC6 (3-o-C8 HSL overproducer), but not when
streaked against itself; (d) strain A136 (PCF218)(PCF372) expressinglacZin
response toP. aeruginosaPAO1 and Pseudomonas chlororaphis(formerly
P. aureofaciens) 30-84 [33]


Bioassays of Quorum and Biofilm Dispersion Signals 7
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