Chapter 1
Use of Whole-Cell Bioassays for Screening Quorum
Signaling, Quorum Interference, and Biofilm Dispersion
Starla G. Thornhill and Robert J.C. McLean
Abstract
In most bacteria, a global level of regulation, termed quorum sensing (QS), exists involving intercellular
communication via the production and response to cell density-dependent signal molecules. QS has been
associated with a number of important features in bacteria including virulence regulation and biofilm
formation. Consequently, there is considerable interest in understanding, detecting, and inhibiting QS.
N-acylated homoserine lactones (AHLs) are used as extracellular QS signals by a variety of Gram-negative
bacteria.Chromobacterium violaceum, commonly found in soil and water, produces the characteristic
purple pigment violacein, regulated by AHL-mediated QS. Based on this readily observed pigmentation
phenotype,C. violaceumstrains can be used to detect various aspects of AHL-mediated QS activity. In
another commonly used bioassay organism,Agrobacterium tumefaciens, QS can be detected by the use of a
reporter gene such aslacZ. Here, we describe several commonly used approaches incorporatingC.
violaceumandA. tumefaciensthat can be used to detect AHL and QS inhibitors. Due to the inherent
low susceptibility of biofilm bacteria to antimicrobial agents, biofilm dispersion, whereby bacteria reenter
the planktonic community, is another increasingly important area of research. At least one signal, distinct
from traditional QS, has been identified and there are a variety of other environmental factors that also
trigger dispersion. We describe a microtiter-based experimental strategy whereby potential biofilm disper-
sion compounds can be screened.
Key wordsQuorum sensing,N-acyl homoserine lactones, Violacein,Chromobacterium violaceum,
Agrobacterium tumefaciens, Biofilm dispersion1 Introduction
This chapterhas been revisedand updatedfromanearlier version[1].1.1 Quorum
Sensing Detection
in Gram-Negative
Bacteria
Population-dependent gene expression, commonly referred to as
quorum sensing (QS), was first associated with light production
inVibrio fischeri[2]. QS is now recognized as a major component of
gene regulation and intercellular communication in bacteria [3, 4]
and is considered to be involved in other aspects of microorganisms
including competition and biofilm structure [5]. QS is an environ-
mental sensing system that allows bacteria to monitor populationLivia Leoni and Giordano Rampioni (eds.),Quorum Sensing: Methods and Protocols, Methods in Molecular Biology,
vol. 1673,https://doi.org/10.1007/978-1-4939-7309-5_1,©Springer Science+Business Media LLC 2018
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