Genetic Diversity as Consequence of a Microaerobic and Neutrophilic Lifestyle

Profiling of the Helicobacter pylori redox switch HP1021 regulon using a multi-omics approach

The gastric human pathogen Helicobacter pylori has developed mechanisms to combat stress factors, including reactive oxygen species (ROS). Here, we present a comprehensive study on the redox switch protein HP1021 regulon combining transcriptomic, proteomic and DNA-protein interactions analyses. Our results indicate that HP1021 modulates H. pylori's response to oxidative stress. HP1021 controls the transcription of 497 genes, including 407 genes related to response to oxidative stress. 79 proteins are differently expressed in the HP1021 deletion mutant. HP1021 controls typical ROS response pathways (katA, rocF) and less canonical ones, particularly DNA uptake and central carbohydrate metabolism. HP1021 is a molecular regulator of competence in H. pylori, as HP1021-dependent repression of the comB DNA uptake genes is relieved under oxidative conditions, increasing natural competence. Furthermore, HP1021 controls glucose consumption by directly regulating the gluP transporter and has an important impact on maintaining the energetic balance in the cell.

DNA Transport through the Dynamic Type IV Secretion System

The versatile type IV secretion system (T4SS) nanomachine plays a pivotal role in bacterial pathogenesis and the propagation of antibiotic resistance determinants throughout microbial populations. In addition to paradigmatic DNA conjugation machineries, diverse T4SSs enable the delivery of multifarious effector proteins to target prokaryotic and eukaryotic cells, mediate DNA export and uptake from the extracellular milieu, and in rare examples, facilitate transkingdom DNA translocation. Recent advances have identified new mechanisms underlying unilateral nucleic acid transport through the T4SS apparatus, highlighting both functional plasticity and evolutionary adaptations that enable novel capabilities. In this review, we describe the molecular mechanisms underscoring DNA translocation through diverse T4SS machineries, emphasizing the architectural features that implement DNA exchange across the bacterial membrane and license transverse DNA release across kingdom boundaries. We further detail how recent studies have addressed outstanding questions surrounding the mechanisms by which nanomachine architectures and substrate recruitment strategies contribute to T4SS functional diversity.

Strategies adopted by gastric pathogen Helicobacter pylori for a mature biofilm formation: Antimicrobial peptides as a visionary treatment

Enormous efforts in recent past two decades to eradicate the pathogen that has been prevalent in half of the world's population have been problematic. The biofilm formed by Helicobacter pylori provides resistance towards innate immune cells, various combinatorial antibiotics, and human antimicrobial peptides, despite the fact that these all are potent enough to eradicate it in vitro. Biofilm provides the opportunity to secrete various virulence factors that strengthen the interaction between host and pathogen helping in evading the innate immune system and ultimately leading to persistence. To our knowledge, this review is the first of its kind to explain briefly the journey of H. pylori starting with the chemotaxis, the mechanism for selecting the site for colonization, the stress faced by the pathogen, and various adaptations to evade these stress conditions by forming biofilm and the morphological changes acquired by the pathogen in mature biofilm. Furthermore, we have explained the human GI tract antimicrobial peptides and the reason behind the failure of these AMPs, and how encapsulation of Pexiganan-A(MSI-78A) in a chitosan microsphere increases the efficiency of eradication.

Cj0683 Is a Competence Protein Essential for Efficient Initialization of DNA Uptake in Campylobacter jejuni

C. jejuni is an important food-borne pathogen displaying high genetic diversity, substantially based on natural transformation. The mechanism of DNA uptake from the environment depends on a type II secretion/type IV pilus system, whose components are partially known. Here, we quantified DNA uptake in C. jejuni at the single cell level and observed median transport capacities of approximately 30 kb per uptake location. The process appeared to be limited by the initialization of DNA uptake, was finite, and, finalized within 30 min of contact to DNA. Mutants lacking either the outer membrane pore PilQ or the inner membrane channel ComEC were deficient in natural transformation. The periplasmic DNA binding protein ComE was negligible for DNA uptake, which is in contrast to its proposed function. Intriguingly, a mutant lacking the unique periplasmic protein Cj0683 displayed rare but fully functional DNA uptake events. We conclude that Cj0683 was essential for the efficient initialization of DNA uptake, consistent with the putative function as a competence pilus protein. Unravelling features important in natural transformation might lead to target identification, reducing the adaptive potential of pathogens.

The Helicobacter pylori UvrC Nuclease Is Essential for Chromosomal Microimports after Natural Transformation

Helicobacter pylori is a Gram-negative bacterial carcinogenic pathogen that infects the stomachs of half of the human population. It is a natural mutator due to a deficient DNA mismatch repair pathway and is naturally competent for transformation. As a result, it is one of the most genetically diverse human bacterial pathogens. The length of chromosomal imports in H. pylori follows an unusual bimodal distribution consisting of macroimports with a mean length of 1,645 bp and microimports with a mean length of 28 bp. The mechanisms responsible for this import pattern were unknown. Here, we used a high-throughput whole-genome transformation assay to elucidate the role of nucleotide excision repair pathway (NER) components on import length distribution. The data show that the integration of microimports depended on the activity of the UvrC endonuclease, while none of the other components of the NER pathway was required. Using H. pylori site-directed mutants, we showed that the widely conserved UvrC nuclease active sites, while essential for protection from UV light, one of the canonical NER functions, are not required for generation of microimports. A quantitative analysis of recombination patterns based on over 1,000 imports from over 200 sequenced recombinant genomes showed that microimports occur frequently within clusters of multiple imports, strongly suggesting they derive from a single strand invasion event. We propose a hypothetical model of homologous recombination in H. pylori, involving a novel function of UvrC, that reconciles the available experimental data about recombination patterns in H. pylori. IMPORTANCE Helicobacter pylori is one of the most common and genetically diverse human bacterial pathogens. It is responsible for chronic gastritis and represents the main risk factor for gastric cancer. In H. pylori, DNA fragments can be imported by recombination during natural transformation. The length of those fragments determines how many potentially beneficial or deleterious alleles are acquired and thus influences adaptation to the gastric niche. Here, we used a transformation assay to examine imported fragments across the chromosome. We show that UvrC, an endonuclease involved in DNA repair, is responsible for the specific integration of short DNA fragments. This suggests that short and long fragments are imported through distinct recombination pathways. We also show that short fragments are frequently clustered with longer fragments, suggesting that both pathways may be mechanistically linked. These findings provide a novel basis to explain how H. pylori can fine-tune the genetic diversity acquired by transformation.

Persistent advanced periductal fibrosis is associated with cagA-positive Helicobacter pylori infection in post-praziquantel treatment of opisthorchiasis

BACKGROUND

Liver fluke infection caused by Opisthorchis viverrini is associated with several hepatobiliary diseases including advanced periductal fibrosis (APF) and cholangiocarcinoma. Recently, we demonstrated a persistent APF in over one-third of opisthorchiasis patients after worm removal by praziquantel (PZQ) treatment. However, the underlying mechanism(s) of this phenomena is unclear. Given a co-infection with Helicobacter pylori (H. pylori) especially cagA-positive strain enhances APF, we hypothesized that H. pylori with CagA virulent factor contributes to persistent APF.

MATERIALS AND METHODS

Seventy-five opisthorchiasis patients who underwent ultrasonography and treatment with PZQ were recruited in the 2-year follow-up study. Helicobacter and its cagA in the feces were examined by conventional and qPCR. Correlations between prevalence or bacterial loads of Helicobacter spp., H. pylori, and cagA-positive H. pylori before and after PZQ treatment were analyzed among resolved, slowly resolved, relapsed, and persistent APF groups.

RESULTS

Overall, prevalence of Helicobacter spp., H. pylori, and cagA-positive H. pylori declined after PZQ treatment. However, only the prevalence and bacterial loads of cagA-positive H. pylori detected at 2-year post-treatment were significantly lower than those before treatment (p < .05). In addition, both prevalence and bacterial loads of cagA-positive H. pylori were significantly lower in the resolved APF group after PZQ treatment, while there were no significant changes in the slowly resolved, relapsed, and persistent APF groups. Among the APF subgroups, cagA-positive H. pylori prevalence in both relapsed and persistent APF groups were significantly higher than the resolved APF group.

CONCLUSION

The results support our hypothesis that H. pylori, especially cagA-positive strain, contributes to the relapsed and persistent APF. A supplementary antibiotic treatment for H. pylori to reduce persistent APF and eventually CCA is warranted.

"Take It or Leave It"-Factors Regulating Competence Development and DNA Uptake in Campylobacter jejuni

Campylobacter jejuni has a large adaptive potential due to enormous genetic exchange. Factors regulating natural transformation in this food-borne pathogen are largely unknown but of interest for the application of sustained reduction strategies in the food-processing industry. Using a single cell DNA uptake assay, we visualized that recognition of methylated C. jejuni DNA was essential for the first step of DNA uptake into a DNase resistant state. Transformation rates using a resistance marker correlated with the fraction of competent bacteria, harboring one to maximally four locations of active DNA uptake, not necessarily being located at the cell pole. Competence developed with rising pH between 6.5 and 7.5 under microaerobic conditions and was nearly insensitive towards growth temperatures between 32 °C and 42 °C, CO₂ concentrations ranging from 0 to 50% and growth rates. However, competence development was abolished at pH 5 or under aerobic stress conditions, in which the bacteria ceased growth but fully survived. The DNA uptake machinery in competent bacteria shut down at slightly acidic pH and was reversibly switched on upon neutralization. It was dependent on the proton motive force and, in contrast to competence development, slightly enhanced under aerobic conditions. The results suggest that natural transformation in C. jejuni occurs in the neutral and microaerobic intestinal environment for enhanced genetic diversity and pre-adaption before host switch. In addition, highly competent bacteria might be shed into the environment, still able to acquire genetic material for increased survival.

Evolved to vary: genome and epigenome variation in the human pathogen Helicobacter pylori

Helicobacter pylori is a Gram-negative, spiral shaped bacterium that selectively and chronically infects the gastric mucosa of humans. The clinical course of this infection can range from lifelong asymptomatic infection to severe disease, including peptic ulcers or gastric cancer. The high mutation rate and natural competence typical of this species are responsible for massive inter-strain genetic variation exceeding that observed in all other bacterial human pathogens. The adaptive value of such a plastic genome is thought to derive from a rapid exploration of the fitness landscape resulting in fast adaptation to the changing conditions of the gastric environment. Nevertheless, diversity is also lost through recurrent bottlenecks and H. pylori's lifestyle is thus a perpetual race to maintain an appropriate pool of standing genetic variation able to withstand selection events. Another aspect of H. pylori's diversity is a large and variable repertoire of restriction-modification systems. While not yet completely understood, methylome evolution could generate enough transcriptomic variation to provide another intricate layer of adaptive potential. This review provides an up to date synopsis of this rapidly emerging area of H. pylori research that has been enabled by the ever-increasing throughput of Omics technologies and a multitude of other technological advances.

HP1021 is a redox switch protein identified in Helicobacter pylori

Helicobacter pylori is a gram-negative, microaerophilic, pathogenic bacterium and a widespread colonizer of humans. H. pylori has developed mechanisms that enable it to overcome the harsh environment of the human stomach, including reactive oxygen species (ROS). Interestingly, up to now no typical regulator dedicated to the oxidative-stress response has been discovered. In this work, we reveal that the inhibitor of replication initiation HP1021 functions as a redox switch protein in H. pylori and plays an important role in response to oxidative stress of the gastric pathogen. Each of the two predicted HP1021 domains contains three cysteine residues. We show that the cysteine residues of HP1021 are sensitive to oxidation both in vitro and in vivo, and we demonstrate that HP1021 DNA-binding activity to oriC depends on the redox state of the protein. Moreover, Zn²⁺ modulates HP1021 affinity towards oriC template DNA. Transcription analysis of selected H. pylori genes by RT-qPCR indicated that HP1021 is directly involved in the oxygen-dependent control of H. pylori fecA3 and gluP genes, which are implicated in response to oxidative stress. In conclusion, HP1021 is a redox switch protein and could be a target for H. pylori control strategies.

Biofilm Formation as a Complex Result of Virulence and Adaptive Responses of Helicobacter pylori

Helicobacter pylori is a bacterium that is capable of colonizing a host for many years, often for a lifetime. The survival in the gastric environment is enabled by the production of numerous virulence factors conditioning adhesion to the mucosa surface, acquisition of nutrients, and neutralization of the immune system activity. It is increasingly recognized, however, that the adaptive mechanisms of H. pylori in the stomach may also be linked to the ability of this pathogen to form biofilms. Initially, biofilms produced by H. pylori were strongly associated by scientists with water distribution systems and considered as a survival mechanism outside the host and a source of fecal-oral infections. In the course of the last 20 years, however, this trend has changed and now the most attention is focused on the biomedical aspect of this structure and its potential contribution to the therapeutic difficulties of H. pylori. Taking into account this fact, the aim of the current review is to discuss the phenomenon of H. pylori biofilm formation and present this mechanism as a resultant of the virulence and adaptive responses of H. pylori, including morphological transformation, membrane vesicles secretion, matrix production, efflux pump activity, and intermicrobial communication. These mechanisms will be considered in the context of transcriptomic and proteomic changes in H. pylori biofilms and their modulating effect on the development of this complex structure.

Four Chromosomal Type IV Secretion Systems in Helicobacter pylori: Composition, Structure and Function

The pathogenic bacterium Helicobacter pylori is genetically highly diverse and a major risk factor for the development of peptic ulcer disease and gastric adenocarcinoma in humans. During evolution, H. pylori has acquired multiple type IV secretion systems (T4SSs), and then adapted for various purposes. These T4SSs represent remarkable molecular transporter machines, often associated with an extracellular pilus structure present in many bacteria, which are commonly composed of multiple structural proteins spanning the inner and outer membranes. By definition, these T4SSs exhibit central functions mediated through the contact-dependent conjugative transfer of mobile DNA elements, the contact-independent release and uptake of DNA into and from the extracellular environment as well as the secretion of effector proteins in mammalian host target cells. In recent years, numerous features on the molecular functionality of these T4SSs were disclosed. H. pylori encodes up to four T4SSs on its chromosome, namely the Cag T4SS present in the cag pathogenicity island (cagPAI), the ComB system, as well as the Tfs3 and Tfs4 T4SSs, some of which exhibit unique T4SS functions. The Cag T4SS facilitates the delivery of the CagA effector protein and pro-inflammatory signal transduction through translocated ADP-heptose and chromosomal DNA, while various structural pilus proteins can target host cell receptors such as integrins or TLR5. The ComB apparatus mediates the import of free DNA from the extracellular milieu, whereas Tfs3 may accomplish the secretion or translocation of effector protein CtkA. Both Tfs3 and Tfs4 are furthermore presumed to act as conjugative DNA transfer machineries due to the presence of tyrosine recombinases with cognate recognition sequences, conjugational relaxases, and potential origins of transfer (oriT) found within the tfs3 and tfs4 genome islands. In addition, some extrachromosomal plasmids, transposons and phages have been discovered in multiple H. pylori isolates. The genetic exchange mediated by DNA mobilization events of chromosomal genes and plasmids combined with recombination events could account for much of the genetic diversity found in H. pylori. In this review, we highlight our current knowledge on the four T4SSs and the involved mechanisms with consequences for H. pylori adaptation to the hostile environment in the human stomach.

Identification of the periplasmic DNA receptor for natural transformation of Helicobacter pylori

Horizontal gene transfer through natural transformation is a major driver of antibiotic resistance spreading in many pathogenic bacterial species. In the case of Gram-negative bacteria, and in particular of Helicobacter pylori, the mechanisms underlying the handling of the incoming DNA within the periplasm are poorly understood. Here we identify the protein ComH as the periplasmic receptor for the transforming DNA during natural transformation in H. pylori. ComH is a DNA-binding protein required for the import of DNA into the periplasm. Its C-terminal domain displays strong affinity for double-stranded DNA and is sufficient for the accumulation of DNA in the periplasm, but not for DNA internalisation into the cytoplasm. The N-terminal region of the protein allows the interaction of ComH with a periplasmic domain of the inner-membrane channel ComEC, which is known to mediate the translocation of DNA into the cytoplasm. Our results indicate that ComH is involved in the import of DNA into the periplasm and its delivery to the inner membrane translocator ComEC.

Some bacteria can take up DNA molecules from the environment. Here, Damke et al. identify a DNA-binding protein in Helicobacter pylori that is required for DNA import into the periplasm and that interacts with an inner-membrane channel that translocates the DNA into the cytoplasm.

Curcumin Mitigates Immune-Induced Epithelial Barrier Dysfunction by Campylobacter jejuni

Campylobacter jejuni (C. jejuni) is the most common cause of foodborne gastroenteritis worldwide. The bacteria induce diarrhea and inflammation by invading the intestinal epithelium. Curcumin is a natural polyphenol from turmeric rhizome of Curcuma longa, a medical plant, and is commonly used in curry powder. The aim of this study was the investigation of the protective effects of curcumin against immune-induced epithelial barrier dysfunction in C. jejuni infection. The indirect C. jejuni-induced barrier defects and its protection by curcumin were analyzed in co-cultures with HT-29/B6-GR/MR epithelial cells together with differentiated THP-1 immune cells. Electrophysiological measurements revealed a reduction in transepithelial electrical resistance (TER) in infected co-cultures. An increase in fluorescein (332 Da) permeability in co-cultures as well as in the germ-free IL-10^−/− mouse model after C. jejuni infection was shown. Curcumin treatment attenuated the C. jejuni-induced increase in fluorescein permeability in both models. Moreover, apoptosis induction, tight junction redistribution, and an increased inflammatory response—represented by TNF-α, IL-1β, and IL-6 secretion—was observed in co-cultures after infection and reversed by curcumin. In conclusion, curcumin protects against indirect C. jejuni-triggered immune-induced barrier defects and might be a therapeutic and protective agent in patients.

Excision and transfer of an integrating and conjugative element in a bacterial species with high recombination efficiency

Horizontal transfer of mobile genetic elements, such as integrating and conjugative elements (ICEs), plays an important role in generating diversity and maintaining comprehensive pan-genomes in bacterial populations. The human gastric pathogen Helicobacter pylori, which is known for its extreme genetic diversity, possesses highly efficient transformation and recombination systems to achieve this diversity, but it is unclear to what extent these systems influence ICE physiology. In this study, we have examined the excision/integration and horizontal transfer characteristics of an ICE (termed ICEHptfs4) in these bacteria. We show that transfer of ICEHptfs4 DNA during mating between donor and recipient strains is independent of its conjugation genes, and that homologous recombination is much more efficient than site-specific integration into the recipient chromosome. Nevertheless, ICEHptfs4 excision by site-specific recombination occurs permanently in a subpopulation of cells and involves relocation of a circularization-dependent promoter. Selection experiments for excision indicate that the circular form of ICEHptfs4 is not replicative, but readily reintegrates by site-specific recombination. Thus, although ICEHptfs4 harbours all essential transfer genes, and typical ICE functions such as site-specific integration are active in H. pylori, canonical ICE transfer is subordinate to the more efficient general DNA uptake and homologous recombination machineries in these bacteria.

Inhibiting bacterial secretion systems in the fight against antibiotic resistance

Antimicrobial resistance is a mounting global health crisis that threatens a resurgence of life-threatening bacterial infections. Despite intensive drug discovery efforts, the rate of antimicrobial resistance outpaces the discovery of new antibiotic agents. One of the major mechanisms driving the rapid propagation of antibiotic resistance is bacterial conjugation mediated by the versatile type IV secretion system (T4SS). The search for therapeutic compounds that prevent the spread of antibiotic resistance via T4SS-dependent mechanisms has identified several promising molecular scaffolds that disrupt resistance determinant dissemination. In this brief review, we highlight the progress and potential of conjugation inhibitors and anti-virulence compounds that target diverse T4SS machineries. These studies provide a solid foundation for the future development of potent, dual-purpose molecular scaffolds that can be used as biochemical tools to probe type IV secretion mechanisms and target bacterial conjugation in clinical settings to prevent the dissemination of antibiotic resistance throughout microbial populations.

Prokaryotic Information Games: How and When to Take up and Secrete DNA

Besides transduction via bacteriophages natural transformation and bacterial conjugation are the most important mechanisms driving bacterial evolution and horizontal gene spread. Conjugation systems have evolved in eubacteria and archaea. In Gram-positive and Gram-negative bacteria, cell-to-cell DNA transport is typically facilitated by a type IV secretion system (T4SS). T4SSs also mediate uptake of free DNA in Helicobacter pylori, while most transformable bacteria use a type II secretion/type IV pilus system. In this chapter, we focus on how and when bacteria "decide" that such a DNA transport apparatus is to be expressed and assembled in a cell that becomes competent. Development of DNA uptake competence and DNA transfer competence is driven by a variety of stimuli and often involves intricate regulatory networks leading to dramatic changes in gene expression patterns and bacterial physiology. In both cases, genetically homogeneous populations generate a distinct subpopulation that is competent for DNA uptake or DNA transfer or might uniformly switch into competent state. Phenotypic conversion from one state to the other can rely on bistable genetic networks that are activated stochastically with the integration of external signaling molecules. In addition, we discuss principles of DNA uptake processes in naturally transformable bacteria and intend to understand the exceptional use of a T4SS for DNA import in the gastric pathogen H. pylori. Realizing the events that trigger developmental transformation into competence within a bacterial population will eventually help to create novel and effective therapies against the transmission of antibiotic resistances among pathogens.

The type IV secretion system in Helicobacter pylori

Helicobacter pylori (H. pylori) has an essential role in the pathogenesis of gastritis, peptic ulcer disease, mucosa-associated lymphoid tissue lymphoma and gastric cancer. The severity of the host inflammatory responses against the bacteria have been straightly associated with a special bacterial virulence factor, the cag pathogenicity island, which is a type IV secretion system (T4SS) to deliver CagA into the host cells. Besides cag-T4SS, the chromosomes of H. pylori can encode another three T4SSs, including comB, tfs3 and tfs4. In this review, we systematically reviewed the four T4SSs of H. pylori and explored their roles in the pathogenesis of gastroduodenal diseases. The information summarized in this review might provide valuable insights into the pathogenic mechanism for H. pylori.

The use of stool specimens reveals Helicobacter pylori strain diversity in a cohort of adolescents and their family members in a developed country

Helicobacter pylori infection occurs within families but the transmission route is unknown. The use of stool specimens to genotype strains facilitates inclusion of complete families in transmission studies. Therefore, we aimed to use DNA from stools to analyze strain diversity in H. pylori infected families. We genotyped H. pylori strains using specific biprobe qPCR analysis of glmM, recA and hspA. Concentration of H. pylori organisms before DNA isolation enhanced subsequent DNA amplification. We isolated H. pylori DNA from 50 individuals in 13 families. T_m data for at least 2 of the 3 genes and sequencing of the glmM amplicon were analyzed. Similar strains were commonly found in both mothers and children and in siblings. However, 20/50 (40%) individuals had multiple strains and several individuals harbored strains not found in other family members, suggesting that even in developed countries sources of infection outside of the immediate family may exist. Whether infection occurs multiple times or one transmission event with several strains occurs is not known but future studies should aim to analyze strains from children much closer to infection onset. The presence of multiple stains in infected persons has implications for antibiotic sensitivity testing and treatment strategies.

DNA Transfer and Toll-like Receptor Modulation by Helicobacter pylori

Helicobacter pylori is the most common bacterial infection worldwide, and virtually all infected persons develop co-existing gastritis. H. pylori is able to send and receive signals from the gastric mucosa, which enables both host and microbe to engage in a dynamic equilibrium. In order to persist within the human host, H. pylori has adopted dichotomous strategies to both induce inflammation as a means of liberating nutrients while simultaneously tempering the immune response to augment its survival. Toll-like receptors (TLRs) and Nod proteins are innate immune receptors that are present in epithelial cells and represent the first line of defense against pathogens. To ensure persistence, H. pylori manipulates TLR-mediated defenses using strategies that include rendering its LPS and flagellin to be non-stimulatory to TLR4 and TLR5, respectively; translocating peptidoglycan into host cells to induce NOD1-mediated anti-inflammatory responses; and translocating DNA into host cells to induce TLR9 activation.

Recent Advances in Helicobacter pylori Replication: Possible Implications in Adaptation to a Pathogenic Lifestyle and Perspectives for Drug Design

DNA replication is an important step in the life cycle of every cell that ensures the continuous flow of genetic information from one generation to the next. In all organisms, chromosome replication must be coordinated with overall cell growth. Helicobacter pylori growth strongly depends on its interaction with the host, particularly with the gastric epithelium. Moreover, H. pylori actively searches for an optimal microniche within a stomach, and it has been shown that not every microniche equally supports growth of this bacterium. We postulate that besides nutrients, H. pylori senses different, unknown signals, which presumably also affect chromosome replication to maintain H. pylori propagation at optimal ratio allowing H. pylori to establish a chronic, lifelong infection. Thus, H. pylori chromosome replication and particularly the regulation of this process might be considered important for bacterial pathogenesis. Here, we summarize our current knowledge of chromosome and plasmid replication in H. pylori and discuss the mechanisms responsible for regulating this key cellular process. The results of extensive studies conducted thus far allow us to propose common and unique traits in H. pylori chromosome replication. Interestingly, the repertoire of proteins involved in replication in H. pylori is significantly different to that in E. coli, strongly suggesting that novel factors are engaged in H. pylori chromosome replication and could represent attractive drug targets.

ComB proteins expression levels determine Helicobacter pylori competence capacity

Helicobacter pylori chronically colonises half of the world’s human population and is the main cause of ulcers and gastric cancers. Its prevalence and the increase in antibiotic resistance observed recently reflect the high genetic adaptability of this pathogen. Together with high mutation rates and an efficient DNA recombination system, horizontal gene transfer through natural competence makes of H. pylori one of the most genetically diverse bacteria. We show here that transformation capacity is enhanced in strains defective for recN, extending previous work with other homologous recombination genes. However, inactivation of either mutY or polA has no effect on DNA transformation, suggesting that natural competence can be boosted in H. pylori by the persistence of DNA breaks but not by enhanced mutagenesis. The transformation efficiency of the different DNA repair impaired strains correlates with the number of transforming DNA foci formed on the cell surface and with the expression of comB8 and comB10 competence genes. Overexpression of the comB6-B10 operon is sufficient to increase the transformation capacity of a wild type strain, indicating that the ComB complex, present in the bacterial wall and essential for DNA uptake, can be a limiting factor for transformation efficiency.