Affiliation:
1. Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
Abstract
ABSTRACT
The Gram-positive obligate anaerobe
Clostridium difficile
causes potentially fatal intestinal diseases. How this organism regulates virulence gene expression is poorly understood. In many bacterial species, the second messenger cyclic di-GMP (c-di-GMP) negatively regulates flagellar motility and, in some cases, virulence. c-di-GMP was previously shown to repress motility of
C. difficile
. Recent evidence indicates that flagellar gene expression is tightly linked with expression of the genes encoding the two
C. difficile
toxins TcdA and TcdB, which are key virulence factors for this pathogen. Here, the effect of c-di-GMP on expression of the toxin genes
tcdA
and
tcdB
was determined, and the mechanism connecting flagellar and toxin gene expressions was examined. In
C. difficile
, increasing c-di-GMP levels reduced the expression levels of
tcdA
and
tcdB
, as well as that of
tcdR
, which encodes an alternative sigma factor that activates
tcdA
and
tcdB
expression. We hypothesized that the
C. difficile
orthologue of the flagellar alternative sigma factor SigD (FliA; σ
28
) mediates regulation of toxin gene expression in response to c-di-GMP. Indeed, ectopic expression of
sigD
in
C. difficile
resulted in increased expression levels of
tcdR
,
tcdA
, and
tcdB
. Furthermore,
sigD
expression enhanced toxin production and increased the cytopathic effect of
C. difficile
on cultured fibroblasts. Finally, evidence is provided that SigD directly activates
tcdR
expression and that SigD cannot activate
tcdA
or
tcdB
expression independent of TcdR. Taken together, these data suggest that SigD positively regulates toxin genes in
C. difficile
and that c-di-GMP can inhibit both motility and toxin production via SigD, making this signaling molecule a key virulence gene regulator in
C. difficile
.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
108 articles.
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