The first discovery of environmental QSIs came from the Aus-
tralian red macro algae,Delisea pulchrawhich was found to pro-
duce an antifouling cocktail of halogenated furanone compounds
of which some were able to inhibit QS [8]. To increase the effect
against the opportunistic human pathogenP. aeruginosa, synthetic
derivatives where synthesized. Two such halogenated furanone
compounds, C30 [6] and C56 [5, 7] showed significant activity
against QS inP. aeruginosa. The discovery of the ability of haloge-
nated furanones to inhibit QS gave rise to the idea that other
compounds with similar capability could be found in a variety of
ecological niches. Our further search revealed that QSIs can be
extracted from many different natural sources including fungi [9],
herbs [10–13], corals, and sponges [14] (Fig.1).
A multitude of synthetic QSI compounds have been described
in following articles [15–21].
This chapter describes methods we have invented and routinely
use to identify and test the potency of QSIs for their ability to
attenuate transcription of the bulk of QS controlled genes inP.
aeruginosa. We present simple, quantitative LasR and RhlR con-
trolled monitor systems [5], as well as a qualitative method to
identify interference or disruption of important biofilm pheno-
types. Finally, the chapter contains a description of how to evaluate
the target specificity of QSI compounds using DNA microarray
based transcriptomics.2 Materials
2.1 QS Monitor
Screens
- Bacterial monitor strains: LasB-GFP,P. aeruginosa(PAO1-
ATCC) harboring alasB-gfp(ASV) fusion together with Plac-
lasR-mini-Tn5 inserted upstream to enhance the sensitivity
[5], and RhlA-GFP,P. aeruginosa(PAO1-ATCC) harboring a
rhlA-gfp(ASV) fusion together with Plac-lasR-mini-Tn5
inserted upstream to enhance the sensitivity [22]. - Black 96 wells microtiter plates. Black microtiter plates are used
to hinder interference between the wells.
Fig. 1Chemical structures of QS inhibitors produced byPenicilliumspecies (a,b) and synthetic halogenated
furanones (c,d). (a) Patulin, (b) penicillic acid, (c) furonone C30, and (d) furanone C56
276 Tim Holm Jakobsen et al.