[Show abstract][Hide abstract] ABSTRACT: The Escherichia coli NsrR protein is a nitric oxide-sensitive repressor of transcription. The NsrR-binding site is predicted to comprise two copies of an 11 bp motif arranged as an inverted repeat with 1 bp spacing. By mutagenesis we confirmed that both 11 bp motifs are required for maximal NsrR repression of the ytfE promoter. We used chromatin immunoprecipitation and microarray analysis (ChIP-chip) to show that NsrR binds to 62 sites close to the 5' ends of genes. Analysis of the ChIP-chip data suggested that a single 11 bp motif (with the consensus sequence AANATGCATTT) can function as an NsrR-binding site in vivo. NsrR binds to sites in the promoter regions of the fliAZY, fliLMNOPQR and mqsR-ygiT transcription units, which encode proteins involved in motility and biofilm development. Reporter fusion assays confirmed that NsrR negatively regulates the fliA and fliL promoters. A mutation in the predicted 11 bp NsrR-binding site in the fliA promoter impaired repression by NsrR and prevented detectable binding in vivo. Assays on soft-agar confirmed that NsrR is a negative regulator of motility in E. coli K12 and in a uropathogenic strain; surface attachment assays revealed decreased levels of attached growth in the absence of NsrR.
Full-text · Article · Aug 2009 · Molecular Microbiology
[Show abstract][Hide abstract] ABSTRACT: Chromatin immunoprecipitation and microarray (ChIP-chip) analysis showed that the nitric oxide (NO)-sensitive repressor NsrR
from Escherichia coli binds in vivo to the promoters of the tynA and feaB genes. These genes encode the first two enzymes of a pathway that is required for the catabolism of phenylethylamine (PEA)
and its hydroxylated derivatives tyramine and dopamine. Deletion of nsrR caused small increases in the activities of the tynA and feaB promoters in cultures grown on PEA. Overexpression of nsrR severely retarded growth on PEA and caused a marked repression of the tynA and feaB promoters. Both the growth defect and the promoter repression were reversed in the presence of a source of NO. These results
are consistent with NsrR mediating repression of the tynA and feaB genes by binding (in an NO-sensitive fashion) to the sites identified by ChIP-chip. E. coli was shown to use 3-nitrotyramine as a nitrogen source for growth, conditions which partially induce the tynA and feaB promoters. Mutation of tynA (but not feaB) prevented growth on 3-nitrotyramine. Growth yields, mutant phenotypes, and analyses of culture supernatants suggested that
3-nitrotyramine is oxidized to 4-hydroxy-3-nitrophenylacetate, with growth occurring at the expense of the amino group of
3-nitrotyramine. Accordingly, enzyme assays showed that 3-nitrotyramine and its oxidation product (4-hydroxy-3-nitrophenylacetaldehyde)
could be oxidized by the enzymes encoded by tynA and feaB, respectively. The results suggest that an additional physiological role of the PEA catabolic pathway is to metabolize nitroaromatic
compounds that may accumulate in cells exposed to NO.
Full-text · Article · Sep 2008 · Journal of bacteriology
[Show abstract][Hide abstract] ABSTRACT: NsrR is a nitric oxide-sensitive regulator of transcription. In Escherichia coli, NsrR is a repressor of the hmp gene encoding the flavohemoglobin that detoxifies nitric oxide. Three other transcription units (ytfE, ygbA, and hcp-hcr) are known to be subject to regulation by NsrR. This chapter describes experimental and statistical protocols used to identify NsrR-binding sites in the E. coli chromosome using chromatin immunoprecipitation and microarray analysis. The methods are applicable, with suitable modifications, to any regulatory protein and any organism.
No preview · Article · Feb 2008 · Methods in Enzymology
[Show abstract][Hide abstract] ABSTRACT: Microarray studies of the Escherichia coli response to nitric oxide and nitrosative stress have suggested that additional transcriptional regulators of this response
remain to be characterized. We identify here the product of the yjeB gene as a negative regulator of the transcription of the ytfE, hmpA and ygbA genes, all of which are known to be upregulated by nitrosative stress. Transcriptional fusions to the promoters of these
genes were expressed constitutively in a yjeB mutant, indicating that all three are targets for repression by YjeB. An inverted repeat sequence that overlaps the −10 element
of all three promoters is proposed to be a binding site for the YjeB protein. A similar inverted repeat sequence was identified
in the tehA promoter, which is also known to be sensitive to nitrosative stress. The ytfE, hmpA, ygbA, and tehA promoters all caused derepression of a ytfE-lacZ transcriptional fusion when present in the cell in multiple copies, presumably by a repressor titration effect, suggesting
the presence of functional YjeB binding sites in these promoters. However, YjeB regulation of tehA was weak, as judged by the activity of a tehA-lacZ fusion, perhaps because YjeB repression of tehA is masked by other regulatory mechanisms. Promoters regulated by YjeB could be derepressed by iron limitation, which is consistent
with an iron requirement for YjeB activity. The YjeB protein is a member of the Rrf2 family of transcriptional repressors
and shares three conserved cysteine residues with its closest relatives. We propose a regulatory model in which the YjeB repressor
is directly sensitive to nitrosative stress. On the basis of similarity to the nitrite-responsive repressor NsrR from Nitrosomonas europaea, we propose that the yjeB gene of E. coli be renamed nsrR.
Preview · Article · Mar 2006 · Journal of Bacteriology
[Show abstract][Hide abstract] ABSTRACT: Caulobacter crescentus has a dimorphic life cycle composed of a motile stage and a sessile stage. In the sessile stage, C. crescentus is often found tightly attached to a surface through its adhesive holdfast. In this study, we examined the contribution of
growth and external structures to the attachment of C. crescentus to abiotic surfaces. We show that the holdfast is essential but not sufficient for optimal attachment. Rather, adhesion in
C. crescentus is a complex developmental process. We found that the attachment of C. crescentus to surfaces is cell cycle regulated and that growth or energy or both are essential for this process. The initial stage of
attachment occurs in swarmer cells and is facilitated by flagellar motility and pili. Our results suggest that strong attachment
is mediated by the synthesis of a holdfast as the swarmer cell differentiates into a stalked cell.
Full-text · Article · Apr 2004 · Journal of Bacteriology
[Show abstract][Hide abstract] ABSTRACT: The differentiating bacterium Caulobacter crescentus produces two different cell types at each cell division, a motile swarmer cell and an adhesive stalked cell. The stalked cell harbours a stalk, a thin cylindrical extension of the cell surface. The tip of the stalk is decorated with a holdfast, an adhesive organelle composed at least in part of polysaccharides. The synthesis of the stalk and holdfast occur at the same pole during swarmer cell differentiation. Mutations in the hfaABDC gene cluster had been shown to disrupt the attachment of the holdfast to the tip of the stalk, but the role of individual genes was unknown. We used lacZ fusions of various DNA fragments from the hfaABDC region to show that these genes form an operon. In order to analyse the relative contribution of the different genes to holdfast attachment, mutations were constructed for each gene. hfaC was not required for holdfast attachment or binding to surfaces. The hfaA and hfaD mutants shed some holdfast material into the surrounding medium and were partially deficient in binding to surfaces. Unlike hfaA and hfaB mutants, hfaD mutants were still able to form rosettes efficiently. Cells with insertions in hfaB were unable to bind to surfaces, and lectin binding studies indicated that the hfaB mutants had the strongest holdfast shedding phenotype. We determined that HfaB and HfaD are membrane-associated proteins and that HfaB is a lipoprotein. Purification of stalks and cell bodies indicated that both HfaB and HfaD are enriched in the stalk as compared to the cell body. These results suggest that HfaB and HfaD, and probably HfaA, serve to anchor the holdfast to the tip of the stalk.
Preview · Article · Oct 2003 · Molecular Microbiology
[Show abstract][Hide abstract] ABSTRACT: Adhesion to both abiotic and biotic surfaces by the gram-negative prothescate bacterium Caulobacter crescentus is mediated by a polar organelle called the “holdfast,” which enables the bacterium to form stable monolayer biofilms. The
holdfast, a complex polysaccharide composed in part of N-acetylglucosamine, localizes to the tip of the stalk (a thin cylindrical extension of the cell wall and membranes). We report
here the isolation of adhesion mutants with transposon insertions in an uncharacterized gene cluster involved in holdfast
biogenesis (hfs) as well as in previously identified polar development genes (podJ and pleC), and the holdfast attachment genes (hfa). Clean deletions of three of the four genes in the hfs gene cluster (hfsDAB) resulted in a severe holdfast biogenesis phenotype. These mutants do not bind to surfaces or to a fluorescently labeled
lectin, specific for N-acetylglucosamine. Transmission electron microscopy indicated that the hfsDAB mutants fail to synthesize a holdfast at the stalk tip. The predicted hfs gene products have significant sequence similarity to proteins necessary for exopolysaccharide export in gram-negative bacteria.
HfsA has sequence similarity to GumC from Xanthomonas campestris, which is involved in exopolysaccharide export in the periplasm. HfsD has sequence similarity to Wza from Escherichia coli, an outer membrane protein involved in secretion of polysaccharide through the outer membrane. HfsB is a novel protein involved
in holdfast biogenesis. These data suggest that the hfs genes play an important role in holdfast export.
Full-text · Article · Mar 2003 · Journal of Bacteriology