The flgE gene of Campylobacter coli is under the control of the alternative sigma factor sigma54

Campylobacter jejuni: targeting host cells, adhesion, invasion, and survival

Campylobacter jejuni, causing strong enteritis, is an unusual bacterium with numerous peculiarities. Chemotactically controlled motility in viscous milieu allows targeted navigation to intestinal mucus and colonization. By phase variation, quorum sensing, extensive O-and N-glycosylation and use of the flagellum as type-3-secretion system C. jejuni adapts effectively to environmental conditions. C. jejuni utilizes proteases to open cell-cell junctions and subsequently transmigrates paracellularly. Fibronectin at the basolateral side of polarized epithelial cells serves as binding site for adhesins CadF and FlpA, leading to intracellular signaling, which again triggers membrane ruffling and reduced host cell migration by focal adhesion. Cell contacts of C. jejuni results in its secretion of invasion antigens, which induce membrane ruffling by paxillin-independent pathway. In addition to fibronectin-binding proteins, other adhesins with other target structures and lectins and their corresponding sugar structures are involved in host-pathogen interaction. Invasion into the intestinal epithelial cell depends on host cell structures. Fibronectin, clathrin, and dynein influence cytoskeletal restructuring, endocytosis, and vesicular transport, through different mechanisms. C. jejuni can persist over a 72-h period in the cell. Campylobacter-containing vacuoles, avoid fusion with lysosomes and enter the perinuclear space via dynein, inducing signaling pathways. Secretion of cytolethal distending toxin directs the cell into programmed cell death, including the pyroptotic release of proinflammatory substances from the destroyed cell compartments. The immune system reacts with an inflammatory cascade by participation of numerous immune cells. The development of autoantibodies, directed not only against lipooligosaccharides, but also against endogenous gangliosides, triggers autoimmune diseases. Lesions of the epithelium result in loss of electrolytes, water, and blood, leading to diarrhea, which flushes out mucus containing C. jejuni. Together with the response of the immune system, this limits infection time. Based on the structural interactions between host cell and bacterium, the numerous virulence mechanisms, signaling, and effects that characterize the infection process of C. jejuni, a wide variety of targets for attenuation of the pathogen can be characterized. The review summarizes strategies of C. jejuni for host-pathogen interaction and should stimulate innovative research towards improved definition of targets for future drug development. KEY POINTS: • Bacterial adhesion of Campylobacter to host cells and invasion into host cells are strictly coordinated processes, which can serve as targets to prevent infection. • Reaction and signalling of host cell depend on the cell type. • Campylobacter virulence factors can be used as targets for development of antivirulence drug compounds.

Flagellar-dependent motility in Mesorhizobium tianshanense is involved in the early stage of plant host interaction: study of an flgE mutant

Bacterial motility is most likely a critical factor for rhizobium to chemotactically colonize on the root surface prior to infecting leguminous plant hosts. Several studies of the rhizobium flagellar filament have been reported, but little is known about the rhizobium flagellum hook. To investigate the roles of the hook protein in flagellum synthesis in Mesorhizobium tianshanense, the hook protein-encoding gene flgE of M. tianshanense was amplified by PCR and sequenced. Comparison of the deduced amino acid sequences revealed pronounced similarities in Domain 1 and lower similarities in Domain 2, which are supposed to be related to hook structure assembly and antigenic diversity, respectively. The level of transcription of flgE increased along with the cell growth and reached its maximum at the middle log phase. Disruption of the flgE gene caused a flagellar-less phenotype, thereby causing complete loss of swimming ability, modified nutrient-related swarming ability and biofilm formation. Moreover, the absence of flagellar caused decreased bacterial attachment on the root hair, suggesting that flagellar is involved in the early stage of symbiosis process.

Change is good: variations in common biological mechanisms in the epsilonproteobacterial genera Campylobacter and Helicobacter

Microbial evolution and subsequent species diversification enable bacterial organisms to perform common biological processes by a variety of means. The epsilonproteobacteria are a diverse class of prokaryotes that thrive in diverse habitats. Many of these environmental niches are labeled as extreme, whereas other niches include various sites within human, animal, and insect hosts. Some epsilonproteobacteria, such as Campylobacter jejuni and Helicobacter pylori, are common pathogens of humans that inhabit specific regions of the gastrointestinal tract. As such, the biological processes of pathogenic Campylobacter and Helicobacter spp. are often modeled after those of common enteric pathogens such as Salmonella spp. and Escherichia coli. While many exquisite biological mechanisms involving biochemical processes, genetic regulatory pathways, and pathogenesis of disease have been elucidated from studies of Salmonella spp. and E. coli, these paradigms often do not apply to the same processes in the epsilonproteobacteria. Instead, these bacteria often display extensive variation in common biological mechanisms relative to those of other prototypical bacteria. In this review, five biological processes of commonly studied model bacterial species are compared to those of the epsilonproteobacteria C. jejuni and H. pylori. Distinct differences in the processes of flagellar biosynthesis, DNA uptake and recombination, iron homeostasis, interaction with epithelial cells, and protein glycosylation are highlighted. Collectively, these studies support a broader view of the vast repertoire of biological mechanisms employed by bacteria and suggest that future studies of the epsilonproteobacteria will continue to provide novel and interesting information regarding prokaryotic cellular biology.

Evaluation of procedures for outer membrane isolation from Campylobacter jejuni

Although infection with Campylobacter jejuni is one of the leading causes of gastroenteritis worldwide, relatively little is known about the factors that are required to elicit a protective immune response. The need for a vaccine against this pathogen is well recognized and a number of vaccine candidates have been tested with varying degrees of success; however, there is still a lack of a suitable vaccine. To gain a better understanding of the outer-membrane protein components of this organism, a 'gold standard' method to purify the outer membrane is needed. Therefore, we attempted to develop a robust and reliable method which resulted in a pure outer-membrane fraction. A total of nine methodologies were examined and analysed by SDS-PAGE and immunoblotting using subcellular markers for the cytoplasm, cytoplasmic membrane and outer membrane. We found that glycine extraction, differential detergent extraction using Triton X-100, serial extraction using 1 M Tris pH 7, spheroplasting by lysozyme and sonication, and carbonate extraction did not produce pure outer-membrane preparations. However, we identified three methods that provided outer-membrane fractions free from subcellular contamination. Isopycnic centrifugation using a 30-60 % sucrose gradient produced seven fractions free from cytoplasmic or cytoplasmic membrane contamination; however, these fractions did not correspond as well as expected with the typical outer-membrane-associated peak (e.g. Escherichia coli or Salmonella). The spheroplast method using lysozyme alone also resulted in pure outer-membrane fraction, as did carbonate washing of this sample. The extraction of outer membranes using N-lauroylsarcosine (Sarkosyl) produced the purest and most reproducible sample. These outer-membrane preparations will be useful for future studies aimed at identifying C. jejuni surface proteins as vaccine components.

Deletion of a previously uncharacterized flagellar-hook-length control gene fliK modulates the sigma54-dependent regulon in Campylobacter jejuni

A previously unannotated, putative fliK gene was identified in the Campylobacter jejuni genome based on sequence analysis; deletion mutants in this gene had a 'polyhook' phenotype characteristic of fliK mutants in other genera. The mutants greatly overexpressed the sigma(54)-dependent flagellar hook protein FlgE, to form unusual filamentous structures resembling straight flagella in addition to polyhooks. The genome sequence reveals only one gene predicted to encode an orthologue of the NtrC-family activator required for sigma(54)-dependent transcription. Hence, all sigma(54)-dependent genes in the genome would be overexpressed in the fliK mutant together with flgE. Microarray analysis of genome-wide transcription in the mutant showed increased transcription of a subset of genes, often downstream of sigma(54)-dependent promoters identified by a quality-predictive algorithm applied to the whole genome. Assessment of genome-wide transcription in deletion mutants in rpoN, encoding sigma(54), and in the sigma(54)-activator gene flgR, showed reciprocally reduced transcription of genes that were overexpressed in the fliK mutant. The fliA (sigma(28))-dependent regulon was also analysed. Together the data clearly define the roles of the alternative sigma factors RpoN and FliA in flagellar biogenesis in C. jejuni, and identify additional putative members of their respective regulons.

Campylobacter flagella: not just for motility

Campylobacter jejuni and Campylobacter coli are among the major causes of diarrheal disease worldwide. The motility imparted by the polar flagella of these pathogens is required for colonization of the mucus lining of the gastrointestinal tract. However, recent studies have revealed a more complex role for flagella in Campylobacter pathogenesis that includes the ability to secrete non-flagellar proteins that modulate virulence and the co-regulation of secreted and non-secreted virulence factors with the flagella regulon. Campylobacter flagellins are heavily glycosylated and changes in glycan composition affect autoagglutination and microcolony formation on intestinal epithelial cells; these traits are associated with disease in an animal model. Here, these recent advances in our understanding of the multifaceted role of flagella in Campylobacter virulence are summarized.

Diverse roles for HspR in Campylobacter jejuni revealed by the proteome, transcriptome and phenotypic characterization of an hspR mutant

Campylobacter jejuni is a leading cause of bacterial gastroenteritis in the developed world. The role of a homologue of the negative transcriptional regulatory protein HspR, which in other organisms participates in the control of the heat-shock response, was investigated. Following inactivation of hspR in C. jejuni, members of the HspR regulon were identified by DNA microarray transcript profiling. In agreement with the predicted role of HspR as a negative regulator of genes involved in the heat-shock response, it was observed that the transcript amounts of 13 genes were increased in the hspR mutant, including the chaperone genes dnaK, grpE and clpB, and a gene encoding the heat-shock regulator HrcA. Proteomic analysis also revealed increased synthesis of the heat-shock proteins DnaK, GrpE, GroEL and GroES in the absence of HspR. The altered expression of chaperones was accompanied by heat sensitivity, as the hspR mutant was unable to form colonies at 44 degrees C. Surprisingly, transcriptome analysis also revealed a group of 17 genes with lower transcript levels in the hspR mutant. Of these, eight were predicted to be involved in the formation of the flagella apparatus, and the decreased expression is likely to be responsible for the reduced motility and ability to autoagglutinate that was observed for hspR mutant cells. Electron micrographs showed that mutant cells were spiral-shaped and carried intact flagella, but were elongated compared to wild-type cells. The inactivation of hspR also reduced the ability of Campylobacter to adhere to and invade human epithelial INT-407 cells in vitro, possibly as a consequence of the reduced motility or lower expression of the flagellar export apparatus in hspR mutant cells. It was concluded that, in C. jejuni, HspR influences the expression of several genes that are likely to have an impact on the ability of the bacterium to successfully survive in food products and subsequently infect the consumer.

Transcription of sigma54-dependent but not sigma28-dependent flagellar genes in Campylobacter jejuni is associated with formation of the flagellar secretory apparatus

We performed a genetic analysis of flagellar regulation in Campylobacter jejuni, from which we elucidated key portions of the flagellar transcriptional cascade in this bacterium. For this study, we developed a reporter gene system for C. jejuni involving astA, encoding arylsulphatase, and placed astA under control of the sigma 54-regulated flgDE2 promoter in C. jejuni strain 81-176. The astA reporter fusion combined with transposon mutagenesis allowed us to identify genes in which insertions abolished flgDE2 expression; genes identified were on both the chromosome and the plasmid pVir. Included among the chromosomal genes were genes encoding a putative sensor kinase and the sigma 54-dependent transcriptional activator, FlgR. In addition, we identified specific flagellar genes, including flhA, flhB, fliP, fliR and flhF, that are also required for transcription of flgDE2 and are presumably at the beginning of the C. jejuni flagellar transcriptional cascade. Deletion of any of these genes reduced transcription of both flgDE2 and another sigma 54-dependent flagellar gene, flaB, encoding a minor flagellin. Transcription of the sigma 28-dependent gene flaA, encoding the major flagellin, was largely unaffected in the mutants. Further examination of flaA transcription revealed significant sigma 28-independent transcription and only weak repressive activity of the putative anti-sigma 28 factor FlgM. Our study suggests that sigma 54-dependent transcription of flagellar genes in C. jejuni is linked to the formation of the flagellar secretory apparatus. A key difference in the C. jejuni flagellar transcriptional cascade compared with other bacteria that use sigma 28 for transcription of flagellar genes is that a mechanism to repress significantly sigma 28-dependent transcription of flaA in flagellar assembly mutants is absent in C. jejuni.

Secretion of virulence proteins from Campylobacter jejuni is dependent on a functional flagellar export apparatus

Campylobacter jejuni, a gram-negative motile bacterium, secretes a set of proteins termed the Campylobacter invasion antigens (Cia proteins). The purpose of this study was to determine whether the flagellar apparatus serves as the export apparatus for the Cia proteins. Mutations were generated in five genes encoding three structural components of the flagella, the flagellar basal body (flgB and flgC), hook (flgE2), and filament (flaA and flaB) genes, as well as in genes whose products are essential for flagellar protein export (flhB and fliI). While mutations that affected filament assembly were found to be nonmotile (Mot-) and did not secrete Cia proteins (S-), a flaA (flaB+) filament mutant was found to be nonmotile but Cia protein secretion competent (Mot-, S+). Complementation of a flaA flaB double mutant with a shuttle plasmid harboring either the flaA or flaB gene restored Cia protein secretion, suggesting that Cia export requires at least one of the two filament proteins. Infection of INT 407 human intestinal cells with the C. jejuni mutants revealed that maximal invasion of the epithelial cells required motile bacteria that are secretion competent. Collectively, these data suggest that the C. jejuni Cia proteins are secreted from the flagellar export apparatus.

Genome-wide Expression Analyses of Campylobacter jejuni NCTC11168 Reveals Coordinate Regulation of Motility and Virulence by flhA

We examined two variants of the genome-sequenced strain, Campylobacter jejuni NCTC11168, which show marked differences in their virulence properties including colonization of poultry, invasion of Caco-2 cells, and motility. Transcript profiles obtained from whole genome DNA microarrays and proteome analyses demonstrated that these differences are reflected in late flagellar structural components and in virulence factors including those involved in flagellar glycosylation and cytolethal distending toxin production. We identified putative sigma(28) and sigma(54) promoters for many of the affected genes and found that greater differences in expression were observed for sigma(28)-controlled genes. Inactivation of the gene encoding sigma(28), fliA, resulted in an unexpected increase in transcripts with sigma(54) promoters, as well as decreased transcription of sigma(28)-regulated genes. This was unlike the transcription profile observed for the attenuated C. jejuni variant, suggesting that the reduced virulence of this organism was not entirely due to impaired function of sigma(28). However, inactivation of flhA, an important component of the flagellar export apparatus, resulted in expression patterns similar to that of the attenuated variant. These findings indicate that the flagellar regulatory system plays an important role in campylobacter pathogenesis and that flhA is a key element involved in the coordinate regulation of late flagellar genes and of virulence factors in C. jejuni.

The FlgS/FlgR two-component signal transduction system regulates the fla regulon in Campylobacter jejuni

The human pathogen Campylobacter jejuni is a highly motile organism that carries a flagellum on each pole. The flagellar motility is regarded as an important trait in C. jejuni colonization of the intestinal tract, however, the knowledge of the regulation of this important colonization factor is rudimentary. We demonstrate by phosphorylation assays that the sensor FlgS and the response regulator FlgR form a two-component system that is on the top of the Campylobacter flagellum hierarchy. Phosphorylated FlgR is needed to activate RpoN-dependent genes of which the products form the hook-basal body filament complex. By real-time reverse transcriptase-PCR we identified that FlgS, FlgR, RpoN, and FliA belong to the early flagellar genes and are regulated by sigma70. FliD and the putative anti-sigma-factor FlgM are regulated by a sigma54- and sigma28-dependent promoters. Activation of the fla regulon is growth phase-dependent, a 100-fold rpoN mRNA reduction is seen in the early stationary phase compared with the early logarithmic phase. Whereas flaB transcription decreases, flaA transcription increases in early stationary phase. Our data show that the C. jejuni flagellar hierarchy largely differs from that of other bacteria. Phenotypical analysis revealed that unflagellated C. jejuni mutants grow three times faster in broth medium compared with wild-type bacteria. In vivo the C. jejuni flagella are needed to pass the gastrointestinal tract of chickens, but not to colonize the ceaca of the chicken.

Pseudaminic acid, the major modification on Campylobacter flagellin, is synthesized via the Cj1293 gene

Flagellins from Campylobacter jejuni 81-176 and Campylobacter coli VC167 are heavily glycosylated. The major modifications on both flagellins are pseudaminic acid (Pse5Ac7Ac), a nine carbon sugar that is similar to sialic acid, and an acetamidino-substituted analogue of pseudaminic acid (PseAm). Previous data have indicated that PseAm is synthesized via Pse5Ac7Ac in C. jejuni 81-176, but that the two sugars are synthesized using independent pathways in C. coli VC167. The Cj1293 gene of C. jejuni encodes a putative UDP-GlcNAc C6-dehydratase/C4-reductase that is similar to a protein required for glycosylation of Caulobacter crescentus flagellin. The Cj1293 gene is expressed either under the control of a sigma 54 promoter that overlaps the coding region of Cj1292 or as a polycistronic message under the control of a sigma 70 promoter upstream of Cj1292. A mutant in gene Cj1293 in C. jejuni 81-176 was non-motile and non-flagellated and accumulated unglycosylated flagellin intracellularly. This mutant was complemented in trans with the homologous C. jejuni gene, as well as the Helicobacter pylori homologue, HP0840, which has been shown to encode a protein with UDP-GlcNAc C6-dehydratase/C4-reductase activity. Mutation of Cj1293 in C. coli VC167 resulted in a fully motile strain that synthesized a flagella filament composed of flagellin in which Pse5Ac7Ac was replaced by PseAm. The filament from the C. coli Cj1293 mutant displayed increased solubility in SDS compared with the wild-type filament. A double mutant in C. coli VC167, defective in both Cj1293 and ptmD, encoding part of the independent PseAm pathway, was also non-motile and non-flagellated and accumulated unglycosylated flagellin intracellularly. Collectively, the data indicate that Cj1293 is essential for Pse5Ac7Ac biosynthesis from UDP-GlcNAc, and that glycosylation is required for flagella biogenesis in campylobacters.

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.

Mutational and transcriptional analysis of the Campylobacter jejuni flagellar biosynthesis gene flhB

A Campylobacter jejuni gene encoding a homologue of the flagellar biosynthesis gene flhB was identified downstream of the peroxide stress defence gene ahpC. Insertional mutagenesis of the flhB gene rendered C. jejuni non-motile, with most cells aflagellate, although a small number expressed truncated flagella. The absence of FlhB also appeared to affect cell shape, as the majority of cells were straight rather than curved rods. Transcription of the flagellin gene flaA was significantly reduced in the C. jejuni flhB mutants, which also did not express significant amounts of flagellin proteins, indicating that FlhB is an essential protein for subsequent expression of flagellar genes. The transcription start site of the flhB gene, as determined by primer extension, was located 91 bp upstream of the flhB start codon, but no recognizable promoter sequence could be identified immediately upstream of this transcription start site. Transcriptional flhB::lacZ reporter gene fusions confirmed that the flhB gene has its own promoter region, is expressed at very low levels and is transcribed independently of ahpC, and that its transcription is not regulated by iron or growth phase.

Transposon mutagenesis of Campylobacter jejuni identifies a bipartite energy taxis system required for motility

Campylobacter jejuni constitutes the leading cause of bacterial gastroenteritis in the United States and a major cause of diarrhoea worldwide. Little is known about virulence mechanisms in this organism because of the scarcity of suitable genetic tools. We have developed an efficient system of in vitro transposon mutagenesis using a mariner-based transposon and purified mariner transposase. Through in vitro transposition of C. jejuni chromosomal DNA followed by natural transformation of the transposed DNA, large random transposon mutant libraries consisting of approximately 16 000 individual mutants were generated. The first genetic screen of C. jejuni using a transposon-generated mutant library identified 28 mutants defective for flagellar motility, one of the few known virulence determinants of this pathogen. We developed a second genetic system, which allows for the construction of defined chromosomal deletions in C. jejuni, and demonstrated the requirement of sigma28 and sigma54 for motility. In addition, we show that sigma28 is involved in the transcription of flaA and that sigma54 is required for transcription of three other flagellar genes, flaB and flgDE. We also identified two previously uncharacterized genes required for motility encoding proteins that we call CetA and CetB, which mediate energy taxis responses. Through our analysis of the Cet proteins, we propose a unique mechanism for sensing energy levels and mediating energy taxis in C. jejuni.

Genetics of swarming motility in Salmonella enterica serovar typhimurium: critical role for lipopolysaccharide

Salmonella enterica serovar Typhimurium can differentiate into hyperflagellated swarmer cells on agar of an appropriate consistency (0.5 to 0.8%), allowing efficient colonization of the growth surface. Flagella are essential for this form of motility. In order to identify genes involved in swarming, we carried out extensive transposon mutagenesis of serovar Typhimurium, screening for those that had functional flagella yet were unable to swarm. A majority of these mutants were defective in lipopolysaccharide (LPS) synthesis, a large number were defective in chemotaxis, and some had defects in putative two-component signaling components. While the latter two classes were defective in swarmer cell differentiation, representative LPS mutants were not and could be rescued for swarming by external addition of a biosurfactant. A mutation in waaG (LPS core modification) secreted copious amounts of slime and showed a precocious swarming phenotype. We suggest that the O antigen improves surface "wettability" required for swarm colony expansion, that the LPS core could play a role in slime generation, and that multiple two-component systems cooperate to promote swarmer cell differentiation. The failure to identify specific swarming signals such as amino acids, pH changes, oxygen, iron starvation, increased viscosity, flagellar rotation, or autoinducers leads us to consider a model in which the external slime is itself both the signal and the milieu for swarming motility. The model explains the cell density dependence of the swarming phenomenon.

Inferring regulatory elements from a whole genome. An analysis of Helicobacter pylori sigma(80) family of promoter signals

Helicobacter pylori is adapted to life in a unique niche, the gastric epithelium of primates. Its promoters may therefore be different from those of other bacteria. Here, we determine motifs possibly involved in the recognition of such promoter sequences by the RNA polymerase using a new motif identification method. An important feature of this method is that the motifs are sought with the least possible assumptions about what they may look like. The method starts by considering the whole genome of H. pylori and attempts to infer directly from it a description for a family of promoters. Thus, this approach differs from searching for such promoters with a previously established description. The two algorithms are based on the idea of inferring motifs by flexibly comparing words in the sequences with an external object, instead of between themselves. The first algorithm infers single motifs, the second a combination of two motifs separated from one another by strictly defined, sterically constrained distances. Besides independently finding motifs known to be present in other bacteria, such as the Shine-Dalgarno sequence and the TATA-box, this approach suggests the existence in H. pylori of a new, combined motif, TTAAGC, followed optimally 21 bp downstream by TATAAT. Between these two motifs, there is in some cases another, TTTTAA or, less frequently, a repetition of TTAAGC separated optimally from the TATA-box by 12 bp. The combined motif TTAAGCx(21+/-2)TATAAT is present with no errors immediately upstream from the only two copies of the ribosomal 23 S-5 S RNA genes in H. pylori, and with one error upstream from the only two copies of the ribosomal 16 S RNA genes. The operons of both ribosomal RNA molecules are strongly expressed, representing an encouraging sign of the pertinence of the motifs found by the algorithms. In 25 cases out of a possible 30, the combined motif is found with no more than three substitutions immediately upstream from ribosomal proteins, or operons containing a ribosomal protein. This is roughly the same frequency of occurrence as for TTGACAx(15-19)TATAAT (with the same maximum number of substitutions allowed) described as being the sigma(70 )promoter sequence consensus in Bacillus subtilis and Escherichia coli. The frequency of occurrence of the new motif obtained, TTAAGCx(19-23)TATAAT, remains high when all protein genes in H. pylori are considered, as is the case for the TTGACAx(15-19)TATAAT motif in B. subtilis but not in E. coli.

Compilation and analysis of sigma(54)-dependent promoter sequences

Promoters recognized by the RNA-polymerase with the alternative sigma factor sigma(54) (Esigma54) are unique in having conserved positions around -24 and -12 nucleotides upstream from the transcriptional start site, instead of the typical -35 and -10 boxes. Here we compile 186 -24/-12 promoter sequences reported in the literature and generate an updated and extended consensus sequence. The use of the extended consensus increases the probability of identifying genuine -24/-12 promoters. The effect of several reported mutations at the -24/-12 elements on RNA-polymerase binding and promoter strength is discussed in the light of the updated consensus.

Expression of the flgFG operon of Campylobacter jejuni in Escherichia coli yields an extra fusion protein

Two Campylobacter jejuni genes with homology to the Escherichia coli flgF and flgG genes encoding two of the basal body rod proteins were isolated, and the nucleotide sequence was determined and analyzed. These two C. jejuni genes were shown, by Northern hybridization analysis, to function as a single operon (flgFG). Two transcriptional start sites were detected upstream of flgF, corresponding to the two RNA transcripts detected in the Northern blot. Western blot immunoassays using anti-FlgF and anti-FlgG antibodies demonstrated the synthesis of FlgF and FlgG proteins in C. jejuni and in Escherichia coli containing the C. jejuni flgF and flgG genes. Maxicell analysis and Western immunoblots using anti-FlgF antibodies to probe flgFG-encoded proteins in E. coli revealed the presence of a protein with a molecular mass of approximately the combined mass of the FlgF and FlgG proteins. Anti-FlgF antibodies detected in C. jejuni cell extracts the native FlgF protein and also a higher-molecular-weight protein that is likely encoded by the flgF and part of the flgG sequences.

The central, surface-exposed region of the flagellar hook protein FlgE of Campylobacter jejuni shows hypervariability among strains

In a previous study, we observed that monoclonal antibodies raised against the hook protein FlgE of Campylobacter jejuni LIO 36, isolate 5226, bound exclusively to this strain. The aim of this study was to elucidate the molecular basis for these binding specificities. The hook protein-encoding gene flgE of C. jejuni was cloned in Escherichia coli and sequenced. The flgE genes of four additional C. jejuni strains were amplified by PCR and also sequenced. Comparison of the deduced amino acid sequences revealed a high degree of variability in the central parts of the FlgE proteins among the strains, including variable and hypervariable domains. These findings may indicate a selective pressure of C. jejuni hosts, forcing the bacteria to generate variations in surface-exposed antigenic determinants.

The Pseudomonas aeruginosa flagellar cap protein, FliD, is responsible for mucin adhesion

Mucin-specific adhesion of Pseudomonas aeruginosa plays an important role in the initial colonization of this organism in the airways of cystic fibrosis patients. We report here that the flagellar cap protein, FliD, participates in this adhesion process. A polar chromosomal insertional mutation in the P. aeruginosa fliD gene made this organism nonadhesive to mucin in an in vitro mucin adhesion assay. The adhesive phenotype was restored by providing the fliD gene alone on a multicopy plasmid, suggesting involvement of this gene in mucin adhesion of P. aeruginosa. Further supporting this observation, the in vitro competition experiments demonstrated that purified FliD protein inhibited the mucin adhesion of nonpiliated P. aeruginosa PAK-NP, while the same concentrations of PilA and FlaG proteins of P. aeruginosa were ineffective in this function. The regulation of the fliD gene was studied and was found to be unique in that the transcription of the fliD gene was independent of the flagellar sigma factor sigma28. Consistent with this finding, no sigma28 binding sequence could be identified in the fliD promoter region. The results of the beta-galactosidase assays suggest that the fliD gene in P. aeruginosa is regulated by the newly described transcriptional regulator FleQ and the alternate sigma factor sigma54 (RpoN).