Quorum Sensing

Chapter 12

Methods to Study Solo/Orphan Quorum-Sensing Receptors

Vittorio Venturi, Sujatha Subramoni, Anice Sabag-Daigle,

and Brian M.M. Ahmer

Abstract

LuxR solos/orphans are very widespread among Proteobacteria; however they are surprisingly under-
studied given that they are likely to play a major role in cell-cell communication in bacteria. Here we
describe three simple methodologies/approaches that can be used in order to begin to study this subgroup
of quorum sensing-related LuxR receptors.

Key wordsE. coli,Salmonella, LuxR solos, LuxR orphans, SdiA, LuxI, Quorum sensing, Regulon,

Transposon, Transcriptional fusion

1 Introduction

Quorum sensing (QS) is a signaling mechanism that mediates

regulation of bacterial behavior in response to environmental

changes in a population density-dependent manner. In Gram-

negative bacteria the most common and best studied signals thus

far are theN-acyl-homoserine lactones (AHLs); these vary in struc-

ture having acyl chains of different lengths (4–20 carbons) and

different oxidation states at position C3. An archetypical AHL QS

system consists of a LuxI family synthase, which synthesizes the

AHL signal, and a LuxR family regulator, which directly binds the

cognate AHL and consequently affects gene expression [1]. Typi-

cally, LuxI/R AHL QS systems are usually genetically linked either

on the chromosome or the plasmids. AHL QS systems have been

investigated in many Gram-negative proteobacteria and have been

linked with phenotypes that benefit the bacterial AHL-producing

community including production of virulence factors, motility,

nodulation, plasmid transfer, antibiotic production, conjugation,

competence, bioluminescence and biofilm formation [2, 3]. The

increasing availability of new bacterial genomes and their analyses

has revealed several LuxR proteins that lack a cognate LuxI

synthase; these have been named LuxR solos or orphans [4–8].

Livia 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_12,©Springer Science+Business Media LLC 2018

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