Biology Reference
In-Depth Information
transcription regulators (
Korner, Sofia, &Zumft, 2003
). Mutants of either
fur
or
perR
exposed to GSNO maintained the Cgb expression pattern found in
the parental strain. However, a
fur
mutant was more sensitive to GSNO
(
Elvers et al., 2005
): chemical interaction between exogenous RNS and
endogenously generated ROS was suggested. Indeed, hypersensitivity to
nitrosative stress in the
E. coli fur
mutant has been related to the
de-repression of the iron assimilation system, consequently generating oxida-
tive stress (
Mukhopadhyay et al., 2004
). More recently, the insensitivity of a
C. jejuni fur
mutant to inhibition by NOwas reported, and a role for the Fur-
regulated genes in protection against nitrosative stress, related to augmenta-
tion of iron acquisition for repairing of damaged Fe-S and haemproteins, was
suggested (
Monk et al., 2008
).
Mutation of the
cj0466
locus abolished GSNO-mediated Cgb expres-
sion; since Cgb expression was apparently dependent upon the product of
Cj0466 under nitrosative stress conditions, the protein was designated NssR
(nitrosative stress sensing regulator) (
Elvers et al., 2005
). Nonetheless, an
increased sensitivity of the
nssR
mutant to methyl viologen that, in
Campylo-
bacter
, is related to superoxide production (
Purdy, Cawthraw, Dickinson,
Newell, & Park, 1999
) suggests an additional role for this regulator.
The transcriptional response to nitrosative stress, obtained by compari-
son of microarray data from microaerobic batch cultures of wild-type
C. jejuni
in the absence and presence of GSNO, showed up regulation of
eight genes, encoding Cgb (
cj1586
), Ctb (
cj0565c
), four probable integral
membrane proteins (
cj0830
,
cj0851c
,
cj0313
and
cj0430
), a probable peptide
ABC transport system permease protein (
cj1582c
) and a hypothetical protein
with unknown function (
cj0761
)(
Elvers et al., 2005
). However, microarray
data comparing GSNO-treated cultures of the wild type and the
nssR
mutant defined the scope of the NssR-dependent response;
cgb
,
ctb
,
cj0761
and
cj0830
were upregulated, and this was also confirmed by
RT-PCR (
Elvers et al., 2005
). A more detailed analysis of transcriptional
changes upon addition of GSNO performed in continuous cultures showed
transcriptional up regulation (
2-fold increased) of 97 genes from a total of
1632 genes (
Monk et al., 2008
). Upregulation of the NssR regulon was con-
firmed;
cgb
(320-fold),
ctb
(63.8-fold), Cj0761 (49.7-fold) and Cj0830 (12.3-
fold) and the presence of Cgb and Ctb in cultures treated with GSNO were
demonstrated by proteomic analysis (
Monk et al., 2008
). Interestingly,
nssR
was also modestly upregulated (2.2-fold), suggesting the existence of a
regulatory mechanism affecting the expression of NssR under conditions
of nitrosative stress. Other genes upregulated under this condition were
