Cloning and expression of the hup encoding a histone-like protein of Campylobacter jejuni

The transcriptional landscape of Campylobacter jejuni under iron replete and iron limited growth conditions

The genome-wide Campylobacter jejuni transcriptional response under iron replete and iron limited conditions was characterized using RNA-seq. We have identified 111 novel C. jejuni 5’UTRs and mapped 377 co-transcribed genes into 230 transcriptional operons. In contrast to previous microarray results, the C. jejuni iron stimulon is less extensive than previously believed and consists of 77 iron activated genes and 50 iron repressed genes. As anticipated, the iron repressed genes are primarily those involved in iron acquisition or oxidative stress defense. Interestingly, these experiments have revealed that iron is an important modulator of flagellar biogenesis with almost all the components of the flagella found to be iron activated. Given that motility is a well-known C. jejuni colonization factor, this suggests that there is an important regulatory coupling of flagellar biogenesis and iron level in C. jejuni. In addition we have identified several consensus mutations in the C. jejuni NCTC11168 strain that are widespread in the Campylobacter research community and which may explain conflicting phenotypic reports for this strain. Comparative analysis of iron responsive genes with the known Fur regulon indicates that many iron responsive genes are not Fur responsive; suggesting that additional iron regulatory factors remain to be characterized in C. jejuni. Further analysis of the RNA-seq data identified multiple novel transcripts including 19 potential ncRNAs. The expression of selected ncRNAs was confirmed and quantified with qRT-PCR. The qRT-PCR results indicate that several of these novel transcripts are either Fur and/or iron responsive. The fact that several of these ncRNAs are iron responsive or Fur regulated suggests that they may perform regulatory roles in iron homeostasis.

Campylobacter jejuni CsrA mediates oxidative stress responses, biofilm formation, and host cell invasion

The putative global posttranscriptional regulator csrA was mutated in Campylobacter jejuni 81-176. The csrA mutant was attenuated in surviving oxidative stress. CsrA also contributed to biofilm formation and adherence to and invasion of INT407 intestinal epithelial cells, suggesting a regulatory role for CsrA in C. jejuni pathogenesis.

Speciation of Campylobacter coli, C. jejuni, C. helveticus, C. lari, C. sputorum, and C. upsaliensis by matrix-assisted laser desorption ionization-time of flight mass spectrometry

Multiple strains of Campylobacter coli, C. jejuni, C. helveticus, C. lari, C. sputorum, and C. upsaliensis isolated from animal, clinical, or food samples have been analyzed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Whole bacterial cells were harvested from colonies or confluent growth on agar and transferred directly into solvent and then to a spot of dried 3-methoxy-4-hydroxycinnamic acid (matrix). Multiple ions in the 5,000- to 15,000-Da mass range were evident in spectra for each strain; one or two ions in the 9,500- to 11,000-Da range were consistently high intensity. "Species-identifying" biomarker ions (SIBIs) were evident from analyses of multiple reference strains for each of the six species, including the genome strains C. jejuni NCTC 11168 and C. jejuni RM1221. Strains grown on nine different combinations of media and atmospheres yielded SIBI masses within +/-5 Da with external instrument calibration. The highest-intensity C. jejuni SIBIs were cytosolic proteins, including GroES, HU/HCj, and RplL. Multiple intraspecies SIBIs, corresponding probably to nonsynonymous nucleotide polymorphisms, also provided some intraspecies strain differentiation. MALDI-TOF MS analysis of 75 additional Campylobacter strains isolated from humans, poultry, swine, dogs, and cats revealed (i) associations of SIBI type with source, (ii) strains previously speciated incorrectly, and (iii) "strains" composed of more than one species. MALDI-TOF MS provides an accurate, sensitive, and rapid method for identification of multiple Campylobacter species relevant to public health and food safety.

Substrate specificity of Helicobacter pylori histone-like HU protein is determined by insufficient stabilization of DNA flexure points

The histone-like HU protein is ubiquitous in the eubacteria. A role for Escherichia coli HU in compaction of the bacterial genome has been reported, along with regulatory roles in DNA replication, transposition, repair and transcription. We show here that HU from the human pathogen Helicobacter pylori, which has been implicated in the development of ulcers and gastric cancer, exhibits enhanced thermal stability and distinct DNA substrate specificity. Thermal denaturation of HpyHU (H. pylori HU) measured by CD spectroscopy yields a melting temperature (T(m)) of 56.4+/-0.1 degrees C. HpyHU binds linear duplex DNA with a site size of approximately 19 bp and with low affinity, but in striking contrast to E. coli HU, HpyHU has only modest preference for DNA with mismatches, nicks or gaps. Instead, HpyHU binds stably to four-way DNA junctions with half-maximal saturation of 5 nM. Substitution of two residues adjacent to the DNA-intercalating prolines attenuates both the preference for flexible DNA and the ability to bend and supercoil DNA. These observations suggest that proline intercalation generates hinges that must be stabilized by adjacent residues; insufficient stabilization leads to reduced bending and a failure to bind preferably to DNA with flexure points, such as gaps and mismatches.

RpoD promoters in Campylobacter jejuni exhibit a strong periodic signal instead of a -35 box

We have used a hidden Markov model (HMM) to identify the consensus sequence of the RpoD promoters in the genome of Campylobacter jejuni. The identified promoter consensus sequence is unusual compared to other bacteria, in that the region upstream of the TATA-box does not contain a conserved -35 region, but shows a very strong periodic variation in the AT-content and semi-conserved T-stretches, with a period of 10-11 nucleotides. The TATA-box is in some, but not all cases, preceded by a TGx, similar to an extended -10 promoter. We predicted a total of 764 presumed RpoD promoters in the C.jejuni genome, of which 654 were located upstream of annotated genes. A similar promoter was identified in Helicobacter pylori, a close phylogenetic relative of Campylobacter, but not in Escherichia coli, Vibrio cholerae, or six other Proteobacterial genomes, or in Staphylococcus aureus. We used upstream regions of high confidence genes as training data (n=529, for the C.jejuni genome). We found it necessary to limit the training set to genes that are preceded by an intergenic region of >100bp or by a gene oriented in the opposite direction to be able to identify a conserved sequence motif, and ended up with a training set of 175 genes. This leads to the conclusion that the remaining genes (354) are more rarely preceded by a (RpoD) promoter, and consequently that operon structure may be more widespread in C.jejuni than has been assumed by others. Structural predictions of the regions upstream of the TATA-box indicates a region of highly curved DNA, and we assume that this facilitates the wrapping of the DNA around the RNA polymerase holoenzyme, and offsets the absence of a conserved -35 binding motif.

Bacterial secreted proteins are required for the internaliztion of Campylobacter jejuni into cultured mammalian cells

Presented here is the first evidence that Campylobacter jejuni secrete proteins upon co-cultivation with host cells and in INT 407 cell-conditioned medium. A C. jejuni gene designated ciaB for Campylobacter invasion antigen B was identified, using a differential screening technique, which is required for this secretion process and the efficient entry of this bacterium into a host cell. The C. jejuni ciaB gene encodes a protein of 610 amino acids with a calculated molecular mass of 73 154 Da. The deduced amino acid sequence of the CiaB protein shares similarity with type III secreted proteins associated with the invasion of host cells from other more extensively characterized bacterial pathogens. In vitro binding and internalization assays revealed that the binding of C. jejuni ciaB null mutants was indistinguishable from that of the parental isolate, whereas a significant reduction was noted in internalization. Confocal microscopic examination of C. jejuni-infected cells revealed that CiaB was translocated into the cytoplasm of the host cells. Culturing C. jejuni with INT 407 cells or in INT 407-conditioned medium resulted in the secretion of at least eight proteins, ranging in size from 12.8 to 108 kDa, into the culture medium. C. jejuni ciaB null mutants were deficient in the secretion of all eight proteins, indicating that CiaB is required for the secretion process. The identification of the C. jejuni ciaB gene represents a significant advance in understanding the molecular mechanism of C. jejuni internalization and the pathogenesis of C. jejuni-mediated enteritis.

Identification of the enteropathogens Campylobacter jejuni and Campylobacter coli based on the cadF virulence gene and its product

Campylobacter jejuni and Campylobacter coli are common causes of gastroenteritis in humans. Infection with C. jejuni or C. coli is commonly acquired by eating undercooked chicken. The goal of this study was to develop specific detection assays for C. jejuni and C. coli isolates based on the cadF virulence gene and its product. The cadF gene from C. jejuni and C. coli encodes a 37-kDa outer membrane protein that promotes the binding of these pathogens to intestinal epithelial cells. A fragment of approximately 400 bp was amplified from 38 of 40 (95%) C. jejuni isolates and 5 of 6 (83.3%) C. coli isolates with primers designed to amplify an internal fragment of the cadF gene. PCR was then used to amplify Campylobacter DNA from store-bought chickens. A 400-bp band was amplified from 26 of the 27 chicken carcasses tested by the PCR-based assay. The CadF protein was detected in every C. jejuni and C. coli isolate tested, as judged by immunoblot analysis with a rabbit anti-C. jejuni 37-kDa serum. In addition, methanol-fixed samples of whole-cell C. jejuni and C. coli were detected with the rabbit anti-37-kDa serum by using an indirect-immunofluorescence microscopy assay. These findings indicate that the cadF gene and its product are conserved among C. jejuni and C. coli isolates and that a PCR assay based on the cadF gene may be useful for the detection of Campylobacter organisms in food products.

Identification of Campylobacter jejuni promoter sequences

A promoterless lacZ shuttle vector, which allowed screening of promoters by beta-galactosidase activity in Campylobacter jejuni and Escherichia coli, was developed. Chromosomal DNA fragments from C. jejuni were cloned into this vector; 125 of 1,824 clones displayed promoter activity in C. jejuni. Eleven clones with strong promoter activity in C. jejuni were further characterized. Their nucleotide sequences were determined, and the transcriptional start sites of the putative promoters in C. jejuni were determined by primer extension. Only 6 of these 11 promoters were functional in E. coli. The 11 newly characterized and 10 previously characterized C. jejuni promoters were used to establish a consensus sequence for C. jejuni promoters. The 21 promoters were found to be very similar. They contain three conserved regions, located approximately 10, 16, and 35 bp upstream of the transcriptional start point. The -10 region resembles that of a typical sigma70 E. coli promoter, but the -35 region is completely different. In addition a -16 region typical for gram-positive bacteria was identified.

Antibodies are generated during infection to Coxiella burnetii macrophage infectivity potentiator protein (Cb-Mip)

Antisera from rabbits immunized with formalin inactivated Coxiella burnetii isolates associated with either acute (Nine Mile, phase I or phase II) or chronic (Priscilla) Q fever showed reactivity to a C. burnetii macrophage infectivity potentiator protein (Cb-Mip) cloned in Escherichia coli. Further, antisera generated in BALB/c mice after infection with live Nine Mile phase I or Priscilla isolates also showed reactivity to Cb-Mip by immunoblot analysis. In addition, human serum from an individual with previous serological and clinical evidence of Q fever showed reactivity to Cb-Mip. This study indicates that Cb-Mip is immunogenic in both experimental and natural infections, and is the first report on the presence of antibodies to Mip/Mip-like proteins of intracellular bacteria in human sera. Cb-Mip may serve as a potential target antigen for developing recombinant vaccines or diagnostic assays for Q fever.

Serratia marcescens contains a heterodimeric HU protein like Escherichia coli and Salmonella typhimurium

Homologs of the dimeric HU protein of Escherichia coli can be found in every prokaryotic organism that has been analyzed. In this work, we demonstrate that Serratia marcescens synthesizes two distinct HU subunits, like E. coli and Salmonella typhimurium, suggesting that the heterodimeric HU protein could be a common feature of enteric bacteria. A phylogenetic analysis of the HU-type proteins (HU and IHF) is presented, and a scheme for the origin of the hup genes and the onset of HU heterodimericity is suggested.