Affiliation:
1. Institute of Infection, Immunity and Inflammation, Centre for Biomolecular
Sciences, University of Nottingham, Nottingham NG7 2RD
2. School of Biosciences, Sutton Bonington Campus, University of Nottingham, Loughborough, Leicestershire LE12 5RD, United Kingdom
3. School of Biology, University of Nottingham, Nottingham NG7 2RD
Abstract
ABSTRACT
Many gram-negative bacteria employ
N
-acylhomoserine lactone
(AHL)-mediated quorum sensing to control virulence. To determine
whether gram-positive bacteria such as
Staphylococcus aureus
respond to AHLs, we used a growth-dependent
lux
reporter
fusion. Exposure of
S. aureus
to different AHLs revealed that
3-oxo-substituted AHLs with C
10
to C
14
acyl
chains inhibited light output and growth in a concentration-dependent
manner, while short-chain AHLs had no effect.
N
-(3-Oxododecanoyl)-
l
-homoserine lactone
(3-oxo-C
12
-HSL) inhibited the production of exotoxins and
cell wall fibronectin-binding proteins but enhanced protein A
expression. Since these processes are reciprocally regulated via the
S. aureus agr
quorum-sensing system, which in turn, is
regulated via
sar
, we examined the effect of AHLs on
sarA
and
agr
. At sub-growth-inhibitory concentrations
of 3-oxo-C
12
-HSL, both
sarA
expression and
agr
expression were inhibited, indicating that the action of
3-oxo-C
12
-HSL is mediated at least in part through
antagonism of quorum sensing in
S. aureus
. Spent culture
supernatants from
Pseudomonas aeruginosa
, which produces both
3-oxo-C
12
-HSL and
N
-butanoyl-homoserine lactone
(C
4
-HSL), also inhibited
agr
expression, although
C
4
-HSL itself was inactive in this assay. Since quorum
sensing in
S. aureus
depends on the activities of
membrane-associated proteins, such as AgrB, AgrC, and AgrD, we
investigated whether AHLs perturbed
S. aureus
membrane
functionality by determining their influence on the membrane dipole
potential. From the binding curves obtained, a dissociation constant of
7 μM was obtained for 3-oxo-C
12
-HSL, indicating the
presence of a specific saturable receptor, whereas no binding was
observed for C
4
-HSL. These data demonstrate that long-chain
3-oxo-substituted AHLs, such as 3-oxo-C
12
-HSL, are capable
of interacting with the
S. aureus
cytoplasmic membrane in a
saturable, specific manner and at sub-growth-inhibitory concentrations,
down-regulating exotoxin production and both
sarA
and
agr
expression.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Immunology,Microbiology,Parasitology
Cited by
134 articles.
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