Sequence divergence and conservation in genomes of Helicobacter cetorum strains from a dolphin and a whale

A Preliminary Comparison on Faecal Microbiomes of Free-Ranging Large Baleen (Balaenoptera musculus, B. physalus, B. borealis) and Toothed (Physeter macrocephalus) Whales

Large baleen and toothed whales play crucial ecological roles in oceans; nonetheless, very little is known about their intestinal microbiomes. Based on striking differences in natural history and thus in feeding behaviours, it can be expected that intestinal microbiomes of large baleen whales and toothed whales are different. To test this hypothesis, the phylogenetic composition of faecal microbiomes was investigated by a 16S rRNA gene amplicon sequence-based approach for Bacteria and Archaea. Faecal samples from free-ranging large whales collected off the Azores Archipelago (Portugal) were used, comprising 13 individual baleen whales (one sei, two blue and ten fin whales) and four sperm whales. The phylogenetic composition of the Bacteria faecal microbiomes of baleen and toothed whales showed no significant differences at the phylum level. However, significant differences were detected at the family and genus levels. Most abundant phyla were Firmicutes, Bacteroidetes, Proteobacteria, Tenericutes and Spirochaeta. Few highly abundant bacterial genera were identified as key taxa with a high contribution to differences among baleen and toothed whales microbiomes. Only few archaeal sequences were detected, primarily Methanomassiliicoccales representing potential methanogenic Archaea. This is the first study that directly compares the faecal bacterial and archaeal microbiomes of free-ranging baleen and toothed whales which represent the two parvorders of Cetacea which members are fully aquatic large mammals which were evolutionary split millions of years ago.

Helicobacter delphinicola sp. nov., isolated from common bottlenose dolphins Tursiops truncatus with gastric diseases

Gastritis and gastric ulcers are well-recognized symptoms in cetaceans, and the genus Helicobacter is considered as the main cause. In this study, we examined the gastric fluid of captive common bottlenose dolphins Tursiops truncatus with gastric diseases in order to isolate the organisms responsible for diagnosis and treatment. Four Gram-negative, rod-shaped isolates (TSBT, TSH1, TSZ, and TSH3) with tightly coiled spirals with 2-4 turns and 2-6 bipolar, sheathed flagella, were obtained from gastric fluids of common bottlenose dolphins with gastric diseases. Phylogenetic analysis, based on 16S rRNA, atpA, and 60 kDa heat-shock protein (hsp60) genes, demonstrated that these isolates form a novel lineage within the genus Helicobacter. Analyses of 16S rRNA, atpA, and hsp60 gene sequences showed that isolate TSBT was most closely related to H. cetorum MIT99-5656T (98.5% similarity), H. pylori ATCC 43504T (76.7% similarity), and H. pylori ATCC 43504T (78.0% similarity), respectively. Type strains of Helicobacter showing resistance to 2% NaCl have not been reported previously; however, these novel isolates were resistant to 2% NaCl. Culture supernatant of some isolates induced intracellular vacuolization in mammalian cultured cells. These data, together with the different morphological and biochemical characteristics of the isolates, reveal that these isolates represent a novel species for which we propose the name Helicobacter delphinicola sp. nov. with type strain TSBT (= JCM 32789T = TSD-183T). Future studies will confirm whether H. delphinicola plays a role in lesion etiopathogenesis in cetaceans.

Complete Genome Sequencing of Four Arcobacter Species Reveals a Diverse Suite of Mobile Elements

Arcobacter species are recovered from a wide variety of sources, including animals, food, and both fresh and marine waters. Several Arcobacter species have also been recovered from human clinical samples and are thus associated tentatively with food- and water-borne human illnesses. Genome sequencing of the poultry isolate Arcobacter cibarius H743 and the Arcobacter acticola, Arcobacter pacificus, and Arcobacter porcinus type strains identified a large number and variety of insertion sequences. This study presents an analysis of these A. acticola, A. cibarius, A. pacificus, and A. porcinus IS elements. The four genomes sequenced here contain 276 complete and degenerate IS elements, representing 13 of the current 29 prokaryotic IS element families. Expansion of the analysis to include 15 other previously sequenced Arcobacter spp. added 73 complete and degenerate IS elements. Several of these IS elements were identified in two or more Arcobacter species, suggesting movement by horizontal gene transfer between the arcobacters. These IS elements are putatively associated with intragenomic deletions and inversions, and tentative movement of antimicrobial resistance genes. The A. cibarius strain H743 megaplasmid contains multiple IS elements common to the chromosome and, unusually, a complete ribosomal RNA locus, indicating that larger scale genomic rearrangements, potentially resulting from IS element-mediated megaplasmid cointegration and resolution may be occurring within A. cibarius and possibly other arcobacters. The presence of such a large and varied suite of mobile elements could have profound effects on Arcobacter biology and evolution.

Comparison of α2,6-sialyltransferases for sialylation of therapeutic proteins

The development of therapeutic proteins for the treatment of numerous diseases is one of the fastest growing areas of biotechnology. Therapeutic efficacy and serum half-life are particularly important, and these properties rely heavily on the glycosylation state of the protein. Expression systems to produce authentically fully glycosylated therapeutic proteins with appropriate terminal sialic acids are not yet perfected. The in vitro modification of therapeutic proteins by recombinant sialyltransferases offers a promising and elegant strategy to overcome this problem. Thus, the detailed expression and characterization of sialyltransferases for completion of the glycan chains is of great interest to the community. We identified a novel α2,6-sialyltransferase from Helicobacter cetorum and compared it to the human ST6Gal1 and a Photobacterium sp. sialyltransferase using glycoprotein substrates in a 96-well microtiter-plate-based assay. We demonstrated that the recombinant α2,6-sialyltransferase from H. cetorum is an excellent catalyst for modification of N-linked glycans of different therapeutic proteins.

Detection and variability analyses of CRISPR-like loci in the H. pylori genome

Helicobacter pylori is a human pathogenic bacterium with a high genomic plasticity. Although the functional CRISPR-Cas system has not been found in its genome, CRISPR-like loci have been recently identified. In this work, 53 genomes from different geographical areas are analyzed for the search and analysis of variability of this type of structure. We confirm the presence of a locus that was previously described in the VlpC gene in al lgenomes, and we characterize new CRISPR-like loci in other genomic locations. By studying the variability and gene location of these loci, the evolution and the possible roles of these sequences are discussed. Additionally, the usefulness of this type of sequences as a phylogenetic marker has been demonstrated, associating the different strains by geographical area.

In silico proteomic and phylogenetic analysis of the outer membrane protein repertoire of gastric Helicobacter species

Helicobacter (H.) pylori is an important risk factor for gastric malignancies worldwide. Its outer membrane proteome takes an important role in colonization of the human gastric mucosa. However, in zoonotic non-H. pylori helicobacters (NHPHs) also associated with human gastric disease, the composition of the outer membrane (OM) proteome and its relative contribution to disease remain largely unknown. By means of a comprehensive survey of the diversity and distribution of predicted outer membrane proteins (OMPs) identified in all known gastric Helicobacter species with fully annotated genome sequences, we found genus- and species-specific families known or thought to be implicated in virulence. Hop adhesins, part of the Helicobacter-specific family 13 (Hop, Hor and Hom) were restricted to the gastric species H. pylori, H. cetorum and H. acinonychis. Hof proteins (family 33) were putative adhesins with predicted Occ- or MOMP-family like 18-stranded β-barrels. They were found to be widespread amongst all gastric Helicobacter species only sporadically detected in enterohepatic Helicobacter species. These latter are other members within the genus Helicobacter, although ecologically and genetically distinct. LpxR, a lipopolysaccharide remodeling factor, was also detected in all gastric Helicobacter species but lacking as well from the enterohepatic species H. cinaedi, H. equorum and H. hepaticus. In conclusion, our systemic survey of Helicobacter OMPs points to species and infection-site specific members that are interesting candidates for future virulence and colonization studies.

Macroevolution of gastric Helicobacter species unveils interspecies admixture and time of divergence

Since the discovery of the human pathogen Helicobacter pylori, various other Helicobacter species have been identified in the stomach of domesticated and wild mammals. To better understand the evolutionary history of these ecologically similar but genetically distinct species, we analyzed 108 gastric Helicobacter genomes and included 54 enterohepatic Helicobacter genomes for comparison purposes. An admixture analysis supported the presence of an ecological barrier, preventing the genetic exchange between the gastric and enterohepatic Helicobacter species, and unraveled many gene flow events within and across species residing in the stomach. As pets can be colonized by multiple gastric Helicobacter species, the genetic exchange between the canine and feline strains was evident, with H. heilmannii and H. bizzozeronii showing the highest interspecies recombination. An admixture between H. pylori (in particular, the ancestral African strains), H. acinonychis from wild felines and H. cetorum from marine mammals was also identified. Because these latter species do not share the same host, this phenomenon is most likely a remaining signal of shared ancestry. A reconstruction of the time of divergence of the gastric Helicobacter spp. revealed that the domestic animal-related Helicobacter species evolved in parallel with H. pylori and its two closest relatives (H. acinonychis and H. cetorum), rather than together.

Relating Phage Genomes to Helicobacter pylori Population Structure: General Steps Using Whole-Genome Sequencing Data

The review uses the Helicobacter pylori, the gastric bacterium that colonizes the human stomach, to address how to obtain information from bacterial genomes about prophage biology. In a time of continuous growing number of genomes available, this review provides tools to explore genomes for prophage presence, or other mobile genetic elements and virulence factors. The review starts by covering the genetic diversity of H. pylori and then moves to the biologic basis and the bioinformatics approaches used for studding the H. pylori phage biology from their genomes and how this is related with the bacterial population structure. Aspects concerning H. pylori prophage biology, evolution and phylogeography are discussed.

Phylogeographic diversity and mosaicism of the Helicobacter pylori tfs integrative and conjugative elements

Background

The genome of the gastric pathogen Helicobacter pylori is characterised by considerable variation of both gene sequence and content, much of which is contained within three large genomic islands comprising the cag pathogenicity island (cagPAI) and two mobile integrative and conjugative elements (ICEs) termed tfs3 and tfs4. All three islands are implicated as virulence factors, although whereas the cagPAI is well characterised, understanding of how the tfs elements influence H. pylori interactions with different human hosts is significantly confounded by limited definition of their distribution, diversity and structural representation in the global H. pylori population.

Results

To gain a global perspective of tfs ICE population dynamics we established a bioinformatics workflow to extract and precisely define the full tfs pan-gene content contained within a global collection of 221 draft and complete H. pylori genome sequences. Complete (ca. 35-55kbp) and remnant tfs ICE clusters were reconstructed from a dataset comprising > 12,000 genes, from which orthologous gene complements and distinct alleles descriptive of different tfs ICE types were defined and classified in comparative analyses. The genetic variation within defined ICE modular segments was subsequently used to provide a complete description of tfs ICE diversity and a comprehensive assessment of their phylogeographic context. Our further examination of the apparent ICE modular types identified an ancient and complex history of ICE residence, mobility and interaction within particular H. pylori phylogeographic lineages and further, provided evidence of both contemporary inter-lineage and inter-species ICE transfer and displacement.

Conclusions

Our collective results establish a clear view of tfs ICE diversity and phylogeographic representation in the global H. pylori population, and provide a robust contextual framework for elucidating the functional role of the tfs ICEs particularly as it relates to the risk of gastric disease associated with different tfs ICE genotypes.

Electronic supplementary material

The online version of this article (10.1186/s13100-018-0109-4) contains supplementary material, which is available to authorized users.

Genomic structure and insertion sites of Helicobacter pylori prophages from various geographical origins

Helicobacter pylori genetic diversity is known to be influenced by mobile genomic elements. Here we focused on prophages, the least characterized mobile elements of H. pylori. We present the full genomic sequences, insertion sites and phylogenetic analysis of 28 prophages found in H. pylori isolates from patients of distinct disease types, ranging from gastritis to gastric cancer, and geographic origins, covering most continents. The genome sizes of these prophages range from 22.6–33.0 Kbp, consisting of 27–39 open reading frames. A 36.6% GC was found in prophages in contrast to 39% in H. pylori genome. Remarkably a conserved integration site was found in over 50% of the cases. Nearly 40% of the prophages harbored insertion sequences (IS) previously described in H. pylori. Tandem repeats were frequently found in the intergenic region between the prophage at the 3′ end and the bacterial gene. Furthermore, prophage genomes present a robust phylogeographic pattern, revealing four distinct clusters: one African, one Asian and two European prophage populations. Evidence of recombination was detected within the genome of some prophages, resulting in genome mosaics composed by different populations, which may yield additional H. pylori phenotypes.

Comparative Genomics of H. pylori and Non-Pylori Helicobacter Species to Identify New Regions Associated with Its Pathogenicity and Adaptability

The genus Helicobacter is a group of Gram-negative, helical-shaped pathogens consisting of at least 36 bacterial species. Helicobacter pylori (H. pylori), infecting more than 50% of the human population, is considered as the major cause of gastritis, peptic ulcer, and gastric cancer. However, the genetic underpinnings of H. pylori that are responsible for its large scale epidemic and gastrointestinal environment adaption within human beings remain unclear. Core-pan genome analysis was performed among 75 representative H. pylori and 24 non-pylori Helicobacter genomes. There were 1173 conserved protein families of H. pylori and 673 of all 99 Helicobacter genus strains. We found 79 genome unique regions, a total of 202,359bp, shared by at least 80% of the H. pylori but lacked in non-pylori Helicobacter species. The operons, genes, and sRNAs within the H. pylori unique regions were considered as potential ones associated with its pathogenicity and adaptability, and the relativity among them has been partially confirmed by functional annotation analysis. However, functions of at least 54 genes and 10 sRNAs were still unclear. Our analysis of protein-protein interaction showed that 30 genes within them may have the cooperation relationship.

An Overview of Helicobacter pylori VacA Toxin Biology

The VacA toxin secreted by Helicobacter pylori enhances the ability of the bacteria to colonize the stomach and contributes to the pathogenesis of gastric adenocarcinoma and peptic ulcer disease. The amino acid sequence and structure of VacA are unrelated to corresponding features of other known bacterial toxins. VacA is classified as a pore-forming toxin, and many of its effects on host cells are attributed to formation of channels in intracellular sites. The most extensively studied VacA activity is its capacity to stimulate vacuole formation, but the toxin has many additional effects on host cells. Multiple cell types are susceptible to VacA, including gastric epithelial cells, parietal cells, T cells, and other types of immune cells. This review focuses on the wide range of VacA actions that are detectable in vitro, as well as actions of VacA in vivo that are relevant for H. pylori colonization of the stomach and development of gastric disease.

Divergence between the Highly Virulent Zoonotic Pathogen Helicobacter heilmannii and Its Closest Relative, the Low-Virulence "Helicobacter ailurogastricus" sp. nov

Helicobacter heilmannii naturally colonizes the stomachs of dogs and cats and has been associated with gastric disorders in humans. Nine feline Helicobacter strains, classified as H. heilmannii based on ureAB and 16S rRNA gene sequences, were divided into a highly virulent and a low-virulence group. The genomes of these strains were sequenced to investigate their phylogenetic relationships, to define their gene content and diversity, and to determine if the differences in pathogenicity were associated with the presence or absence of potential virulence genes. The capacities of these helicobacters to bind to the gastric mucosa were investigated as well. Our analyses revealed that the low-virulence strains do not belong to the species H. heilmannii but to a novel, closely related species for which we propose the name Helicobacter ailurogastricus. Several homologs of H. pylori virulence factors, such as IceA1, HrgA, and jhp0562-like glycosyltransferase, are present in H. heilmannii but absent in H. ailurogastricus. Both species contain a VacA-like autotransporter, for which the passenger domain is remarkably larger in H. ailurogastricus than in H. heilmannii. In addition, H. ailurogastricus shows clear differences in binding to the gastric mucosa compared to H. heilmannii. These findings highlight the low-virulence character of this novel Helicobacter species.

Transmission of the PabI family of restriction DNA glycosylase genes: mobility and long-term inheritance

Background

R.PabI is an exceptional restriction enzyme that functions as a DNA glycosylase. The enzyme excises an unmethylated base from its recognition sequence to generate apurinic/apyrimidinic (AP) sites, and also displays AP lyase activity, cleaving the DNA backbone at the AP site to generate the 3’-phospho alpha, beta-unsaturated aldehyde end in addition to the 5’-phosphate end. The resulting ends are difficult to religate with DNA ligase. The enzyme was originally isolated in Pyrococcus, a hyperthermophilic archaeon, and additional homologs subsequently identified in the epsilon class of the Gram-negative bacterial phylum Proteobacteria, such as Helicobacter pylori.

Results

Systematic analysis of R.PabI homologs and their neighboring genes in sequenced genomes revealed co-occurrence of R.PabI with M.PabI homolog methyltransferase genes. R.PabI and M.PabI homolog genes are occasionally found at corresponding (orthologous) loci in different species, such as Helicobacter pylori, Helicobacter acinonychis and Helicobacter cetorum, indicating long-term maintenance of the gene pair. One R.PabI and M.PabI homolog gene pair is observed immediately after the GMP synthase gene in both Campylobacter and Helicobacter, representing orthologs beyond genera. The mobility of the PabI family of restriction-modification (RM) system between genomes is evident upon comparison of genomes of sibling strains/species. Analysis of R.PabI and M.PabI homologs in H. pylori revealed an insertion of integrative and conjugative elements (ICE), and replacement with a gene of unknown function that may specify a membrane-associated toxin (hrgC). In view of the similarity of HrgC with toxins in type I toxin-antitoxin systems, we addressed the biological significance of this substitution. Our data indicate that replacement with hrgC occurred in the common ancestor of hspAmerind and hspEAsia. Subsequently, H. pylori with and without hrgC were intermixed at this locus, leading to complex distribution of hrgC in East Asia and the Americas. In Malaysia, hrgC was horizontally transferred from hspEAsia to hpAsia2 strains.

Conclusions

The PabI family of RM system behaves as a mobile, selfish genetic element, similar to the other families of Type II RM systems. Our analysis additionally revealed some cases of long-term inheritance. The distribution of the hrgC gene replacing the PabI family in the subpopulations of H. pylori, hspAmerind, hspEAsia and hpAsia2, corresponds to the two human migration events, one from East Asia to Americas and the other from China to Malaysia.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2021-3) contains supplementary material, which is available to authorized users.

Dormant phages of Helicobacter pylori reveal distinct populations in Europe

Prophages of Helicobacter pylori, a bacterium known to co-evolve in the stomach of its human host, were recently identified. However, their role in the diversity of H. pylori strains is unknown. We demonstrate here and for the first time that the diversity of the prophage genes offers the ability to distinguish between European populations, and that H. pylori prophages and their host bacteria share a complex evolutionary history. By comparing the phylogenetic trees of two prophage genes (integrase and holin) and the multilocus sequence typing (MLST)-based data obtained for seven housekeeping genes, we observed that the majority of the strains belong to the same phylogeographic group in both trees. Furthermore, we found that the Bayesian analysis of the population structure of the prophage genes identified two H. pylori European populations, hpNEurope and hpSWEurope, while the MLST sequences identified one European population, hpEurope. The population structure analysis of H. pylori prophages was even more discriminative than the traditional MLST-based method for the European population. Prophages are new players to be considered not only to show the diversity of H. pylori strains but also to more sharply define human populations.

Complete Genome Sequences of Two Helicobacter pylori Strains from a Canadian Arctic Aboriginal Community

We report here the complete genome sequences of two Amerind Helicobacter pylori strains from Aklavik, Northwest Territories, Canada. One strain contains extra iron-cofactored urease genes and ~140 rearrangements in its chromosome relative to other described strains (typically differing from one another by <10 rearrangements), suggesting that it represents a novel lineage of H. pylori.

Evaluation of two commercially available immunological kits for the diagnosis of Helicobacter spp. in bottlenose dolphins (Tursiops truncatus)

Helicobacter pylori is considered to be responsible for the most common gastric infections in humans worldwide. In animals, other Helicobacter species are linked to gastritis with and without the presence of ulcers in their respective hosts. Moreover, gastric ulcers have been reported for decades in wild and captive dolphins. Clinical signs include lack of appetite, anorexia, abdominal tenderness, depression, and occasional unresponsiveness. In this study, serum and stool of nine bottlenose dolphins from Loro Parque collection Tenerife, Spain were examined for the presence of Helicobacter spp. The aim of our study was to evaluate the use of two commercially available kits for the detection of H. pylori in humans: a stool antigen immunoassay (Letitest H. pylori CARD) and a Western blot assay (EUROLINE-WB H. pylori) that were adapted to identify specific Helicobacter spp. antibodies in the tested Loro Parque bottlenose dolphin collection. The utility of these diagnostic kits for their application in dolphins is demonstrated, and their use in the future for the diagnosis of Helicobacter spp. in both wild and captive dolphins is proposed in this study.

Gastric and enterohepatic helicobacters other than Helicobacter pylori

During the past year, research on non-Helicobacter pylori species has intensified. H. valdiviensis was isolated from wild birds, and putative novel species have been isolated from Bengal tigers and Australian marsupials. Various genomes have been sequenced: H. bilis, H. canis, H. macacae, H. fennelliae, H. cetorum, and H. suis. Several studies highlighted the virulence of non-H. pylori species including H. cinaedi in humans and hyperlipidemic mice or H. macacae in geriatric rhesus monkeys with intestinal adenocarcinoma. Not surprisingly, increased attention has been paid to the position of Helicobacter species in the microbiota of children and animal species (mice, chickens, penguins, and migrating birds). A large number of experimental studies have been performed in animal models of Helicobacter induced typhlocolitis, showing that the gastrointestinal microbial community is involved in modulation of host pathways leading to chronic inflammation. Animal models of H. suis, H. heilmannii, and H. felis infection have been used to study the development of severe inflammation-related pathologies, including gastric MALT lymphoma and adenocarcinoma.

A comprehensive analysis of Helicobacter pylori plasticity zones reveals that they are integrating conjugative elements with intermediate integration specificity

BACKGROUND

The human gastric pathogen Helicobacter pylori is a paradigm for chronic bacterial infections. Its persistence in the stomach mucosa is facilitated by several mechanisms of immune evasion and immune modulation, but also by an unusual genetic variability which might account for the capability to adapt to changing environmental conditions during long-term colonization. This variability is reflected by the fact that almost each infected individual is colonized by a genetically unique strain. Strain-specific genes are dispersed throughout the genome, but clusters of genes organized as genomic islands may also collectively be present or absent.

RESULTS

We have comparatively analysed such clusters, which are commonly termed plasticity zones, in a high number of H. pylori strains of varying geographical origin. We show that these regions contain fixed gene sets, rather than being true regions of genome plasticity, but two different types and several subtypes with partly diverging gene content can be distinguished. Their genetic diversity is incongruent with variations in the rest of the genome, suggesting that they are subject to horizontal gene transfer within H. pylori populations. We identified 40 distinct integration sites in 45 genome sequences, with a conserved heptanucleotide motif that seems to be the minimal requirement for integration.

CONCLUSIONS

The significant number of possible integration sites, together with the requirement for a short conserved integration motif and the high level of gene conservation, indicates that these elements are best described as integrating conjugative elements (ICEs) with an intermediate integration site specificity.