Novel virulent and broad-host-range Erwinia amylovora bacteriophages reveal a high degree of mosaicism and a relationship to Enterobacteriaceae phages

Predicting genome terminus sequences of Bacillus cereus-group bacteriophage using next generation sequencing data

Background

Most tailed bacteriophages (phages) feature linear dsDNA genomes. Characterizing novel phages requires an understanding of complete genome sequences, including the definition of genome physical ends.

Result

We sequenced 48 Bacillus cereus phage isolates and analyzed Next-generation sequencing (NGS) data to resolve the genome configuration of these novel phages. Most assembled contigs featured reads that mapped to both contig ends and formed circularized contigs. Independent assemblies of 31 nearly identical I48-like Bacillus phage isolates allowed us to observe that the assembly programs tended to produce random cleavage on circularized contigs. However, currently available assemblers were not capable of reporting the underlying phage genome configuration from sequence data. To identify the genome configuration of sequenced phage in silico, a terminus prediction method was developed by means of ‘neighboring coverage ratios’ and ‘read edge frequencies’ from read alignment files. Termini were confirmed by primer walking and supported by phylogenetic inference of large DNA terminase protein sequences.

Conclusions

The Terminus package using phage NGS data along with the contig circularity could efficiently identify the proximal positions of phage genome terminus. Complete phage genome sequences allow a proposed characterization of the potential packaging mechanisms and more precise genome annotation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3744-0) contains supplementary material, which is available to authorized users.

Bacteriophages and Bacterial Plant Diseases

Losses in crop yields due to disease need to be reduced in order to meet increasing global food demands associated with growth in the human population. There is a well-recognized need to develop new environmentally friendly control strategies to combat bacterial crop disease. Current control measures involving the use of traditional chemicals or antibiotics are losing their efficacy due to the natural development of bacterial resistance to these agents. In addition, there is an increasing awareness that their use is environmentally unfriendly. Bacteriophages, the viruses of bacteria, have received increased research interest in recent years as a realistic environmentally friendly means of controlling bacterial diseases. Their use presents a viable control measure for a number of destructive bacterial crop diseases, with some phage-based products already becoming available on the market. Phage biocontrol possesses advantages over chemical controls in that tailor-made phage cocktails can be adapted to target specific disease-causing bacteria. Unlike chemical control measures, phage mixtures can be easily adapted for bacterial resistance which may develop over time. In this review, we will examine the progress and challenges for phage-based disease biocontrol in food crops.

PhagePhisher: a pipeline for the discovery of covert viral sequences in complex genomic datasets

Obtaining meaningful viral information from large sequencing datasets presents unique challenges distinct from prokaryotic and eukaryotic sequencing efforts. The difficulties surrounding this issue can be ascribed in part to the genomic plasticity of viruses themselves as well as the scarcity of existing information in genomic databases. The open-source software PhagePhisher (http://www.putonti-lab.com/phagephisher) has been designed as a simple pipeline to extract relevant information from complex and mixed datasets, and will improve the examination of bacteriophages, viruses, and virally related sequences, in a range of environments. Key aspects of the software include speed and ease of use; PhagePhisher can be used with limited operator knowledge of bioinformatics on a standard workstation. As a proof-of-concept, PhagePhisher was successfully implemented with bacteria–virus mixed samples of varying complexity. Furthermore, viral signals within microbial metagenomic datasets were easily and quickly identified by PhagePhisher, including those from prophages as well as lysogenic phages, an important and often neglected aspect of examining phage populations in the environment. PhagePhisher resolves viral-related sequences which may be obscured by or imbedded in bacterial genomes.

Protection of Erwinia amylovora bacteriophage Y2 from UV-induced damage by natural compounds

Bacteriophages have regained much attention as biocontrol agents against bacterial pathogens. However, with respect to stability, phages are biomolecules and are therefore sensitive to a number of environmental influences. UV-irradiation can readily inactivate phage infectivity, which impedes their potential application in the plant phyllosphere. Therefore, phages for control of Erwinia amylovora, the causative agent of fire blight, need to be protected from UV-damage by adequate measures. We investigated the protective effect of different light-absorbing substances on phage particles exposed to UV-light. For this, natural extracts from carrot, red pepper, and beetroot, casein and soy peptone in solution, and purified substances such as astaxanthin, aromatic amino acids, and Tween 80 were prepared and tested as natural sunscreens for phage. All compounds were found to significantly increase half-life of UV-irradiated phage particles and they did not negatively affect phage viability or infectivity. Altogether, a range of readily available, natural substances are suitable as UV-protectants to prevent phage particles from UV-light damage.

Taxonomic reassessment of N4-like viruses using comparative genomics and proteomics suggests a new subfamily - "Enquartavirinae"

The GenBank database currently contains sequence data for 33 N4-like viruses, with only one, Escherichia phage N4, being formally recognized by the ICTV. The genus N4likevirus is uniquely characterized by that fact that its members possess an extremely large, virion-associated RNA polymerase. Using a variety of proteomic, genomic and phylogenetic tools, we have demonstrated that the N4-like phages are not monophyletic and that N4 is actually a genomic orphan. We propose to create four new genera: "G7cvirus" (consisting of phages G7C, IME11, KBNP21, vB_EcoP_PhAPEC5, vB_EcoP_PhAPEC7, Bp4, EC1-UPM and pSb-1), "Lit1virus" (LIT1, PA26 and vB_PaeP_C2-10_Ab09), "Sp58virus" (SP058 and SP076), and "Dss3virus" (DSS3φ2 and EE36φ1). We propose that coliphage N4, the members of "G7cvirus", Erwinia phage Ea9-2, and Achromobacter phage JWAlpha should be considered members of the same subfamily, which we tentatively call the "Enquartavirinae".

Novel N4 Bacteriophages Prevail in the Cold Biosphere

Coliphage N4 is a lytic bacteriophage discovered nearly half a century ago, and it was considered to be a "genetic orphan" until very recently, when several additional N4-like phages were discovered to infect nonenteric bacterial hosts. Interest in this genus of phages is stimulated by their unique genetic features and propagation strategies. To better understand the ecology of N4-like phages, we investigated the diversity and geographic patterns of N4-like phages by examining 56 Chesapeake Bay viral communities, using a PCR-clone library approach targeting a diagnostic N4-like DNA polymerase gene. Many new lineages of N4-like phages were found in the bay, and their genotypes shift from the lower to the upper bay. Interestingly, signature sequences of N4-like phages were recovered only from winter month samples, when water temperatures were below 4°C. An analysis of existing metagenomic libraries from various aquatic environments supports the hypothesis that N4-like phages are most prolific in colder waters. In particular, a high number of N4-like phages were detected in Organic Lake, Antarctica, a cold and hypersaline system. The prevalence of N4-like phages in the cold biosphere suggests these viruses possess yet-to-be-determined mechanisms that facilitate lytic infections under cold conditions.

Absence of lysogeny in wild populations of Erwinia amylovora and Pantoea agglomerans

Lytic bacteriophages are in development as biological control agents for the prevention of fire blight disease caused by Erwinia amylovora. Temperate phages should be excluded as biologicals since lysogeny produces the dual risks of host resistance to phage attack and the transduction of virulence determinants between bacteria. The extent of lysogeny was estimated in wild populations of E. amylovora and Pantoea agglomerans with real-time polymerase chain reaction primers developed to detect E. amylovora phages belonging to the Myoviridae and Podoviridae families. Pantoea agglomerans, an orchard epiphyte, is easily infected by Erwinia spp. phages, and it serves as a carrier in the development of the phage-mediated biological control agent. Screening of 161 E. amylovora isolates from 16 distinct geographical areas in North America, Europe, North Africa and New Zealand and 82 P. agglomerans isolates from southern Ontario, Canada showed that none possessed prophage. Unstable phage resistant clones or lysogens were produced under laboratory conditions. Additionally, a stable lysogen was recovered from infection of bacterial isolate Ea110R with Podoviridae phage ΦEa35-20. These laboratory observations suggested that while lysogeny is possible in E. amylovora, it is rare or absent in natural populations, and there is a minimal risk associated with lysogenic conversion and transduction by Erwinia spp. phages.

Characterization of a new ViI-like Erwinia amylovora bacteriophage phiEa2809

Erwinia amylovora is a Gram-negative plant pathogenic bacteria causing fire blight disease in many Rosaceae species. A novel E. amylovora bacteriophage, phiEa2809, was isolated from symptomless apple leaf sample collected in Belarus. This phage was also able to infect Pantoea agglomerans strains. The genome of phiEa2809 is a double-stranded linear DNA 162,160 bp in length, including 145 ORFs and one tRNA gene. The phiEa2809 genomic sequence is similar to the genomes of the Serratia plymutica phage MAM1, Shigella phage AG-3, Dickeya phage vB DsoM LIMEstone1 and Salmonella phage ViI and lacks similarity to described E. amylovora phage genomes. Based on virion morphology (an icosahedral head, long contractile tail) and genome structure, phiEa2809 was classified as a member of Myoviridae, ViI-like bacteriophages group. PhiEa2809 is the firstly characterized ViI-like bacteriophage able to lyse E. amylovora.

Understanding the enormous diversity of bacteriophages: the tailed phages that infect the bacterial family Enterobacteriaceae

Bacteriophages are the predominant biological entity on the planet. The recent explosion of sequence information has made estimates of their diversity possible. We describe the genomic comparison of 337 fully sequenced tailed phages isolated on 18 genera and 31 species of bacteria in the Enterobacteriaceae. These phages were largely unambiguously grouped into 56 diverse clusters (32 lytic and 24 temperate) that have syntenic similarity over >50% of the genomes within each cluster, but substantially less sequence similarity between clusters. Most clusters naturally break into sets of more closely related subclusters, 78% of which are correlated with their host genera. The largest groups of related phages are superclusters united by genome synteny to lambda (81 phages) and T7 (51 phages). This study forms a robust framework for understanding diversity and evolutionary relationships of existing tailed phages, for relating newly discovered phages and for determining host/phage relationships.

Bacteriophage therapy against Enterobacteriaceae

The Enterobacteriaceae are a class of gram-negative facultative anaerobic rods, which can cause a variety of diseases, such as bacteremia, septic arthritis, endocarditis, osteomyelitis, lower respiratory tract infections, skin and soft-tissue infections, urinary tract infections, intra-abdominal infections and ophthalmic infections, in humans, poultry, animals and fish. Disease caused by Enterobacteriaceae cause the deaths of millions of people every year, resulting in enormous economic loss. Drug treatment is a useful and efficient way to control Enterobacteriaceae infections. However, with the abuse of antibiotics, drug resistance has been found in growing number of Enterobacteriaceae infections and, as such, there is an urgent need to find new methods of control. Bacteriophage therapy is an efficient alternative to antibiotics as it employs a different antibacterial mechanism. This paper summarizes the history of bacteriophage therapy, its bacterial lytic mechanisms, and the studies that have focused on Enterobacteriaceae and bacteriophage therapy.

Integration of genomic and proteomic analyses in the classification of the Siphoviridae family

Using a variety of genomic (BLASTN, ClustalW) and proteomic (Phage Proteomic Tree, CoreGenes) tools we have tackled the taxonomic status of members of the largest bacteriophage family, the Siphoviridae. In all over 400 phages were examined and we were able to propose 39 new genera, comprising 216 phage species, and add 62 species to two previously defined genera (Phic3unalikevirus; L5likevirus) grouping, in total, 390 fully sequenced phage isolates. Many of the remainders are orphans which the Bacterial and Archaeal Viruses Subcommittee of the International Committee on Taxonomy of Viruses (ICTV) chooses not to ascribe genus status at the time being.

Novel group of podovirus infecting the marine bacterium Alteromonas macleodii

Four novel, closely related podoviruses, which displayed lytic activity against the gamma-proteobacterium Alteromonas macleodii, have been isolated and sequenced. Alterophages AltAD45-P1 to P4 were obtained from water recovered near a fish farm in the Mediterranean Sea. Their morphology indicates that they belong to the Podoviridae. Their linear and dsDNA genomes are 100–104 kb in size, remarkably larger than any other described podovirus. The four AltAD45-phages share 99% nucleotide sequence identity over 97% of their ORFs, although an insertion was found in AltAD45-P1 and P2 and some regions were slightly more divergent. Despite the high overall sequence similarity among these four phages, the group with the insertion and the group without it, have different host ranges against the A. macleodii strains tested. The AltAD45-P1 to P4 phages have genes for DNA replication and transcription as well as structural genes, which are similar to the N4-like Podoviridae genus that is widespread in proteobacteria. However, in terms of their genomic structure, AltAD45-P1 to P4 differ from that of the N4-like phages. Some distinguishing features include the lack of a large virion encapsidated RNA polymerase gene, very well conserved among all the previously described N4-like phages, a single-stranded DNA binding protein and different tail protein genes. We conclude that the AltAD45 phages characterized in this study constitute a new genus within the Podoviridae.

Comparative genomics defines the core genome of the growing N4-like phage genus and identifies N4-like Roseophage specific genes

Two bacteriophages, RPP1 and RLP1, infecting members of the marine Roseobacter clade were isolated from seawater. Their linear genomes are 74.7 and 74.6 kb and encode 91 and 92 coding DNA sequences, respectively. Around 30% of these are homologous to genes found in Enterobacter phage N4. Comparative genomics of these two new Roseobacter phages and 23 other sequenced N4-like phages (three infecting members of the Roseobacter lineage and 20 infecting other Gammaproteobacteria) revealed that N4-like phages share a core genome of 14 genes responsible for control of gene expression, replication and virion proteins. Phylogenetic analysis of these genes placed the five N4-like roseophages (RN4) into a distinct subclade. Analysis of the RN4 phage genomes revealed they share a further 19 genes of which nine are found exclusively in RN4 phages and four appear to have been acquired from their bacterial hosts. Proteomic analysis of the RPP1 and RLP1 virions identified a second structural module present in the RN4 phages similar to that found in the Pseudomonas N4-like phage LIT1. Searches of various metagenomic databases, including the GOS database, using CDS sequences from RPP1 suggests these phages are widely distributed in marine environments in particular in the open ocean environment.

The arable ecosystem as battleground for emergence of new human pathogens

Disease incidences related to Escherichia coli and Salmonella enterica infections by consumption of (fresh) vegetables, sprouts, and occasionally fruits made clear that these pathogens are not only transmitted to humans via the "classical" routes of meat, eggs, and dairy products, but also can be transmitted to humans via plants or products derived from plants. Nowadays, it is of major concern that these human pathogens, especially the ones belonging to the taxonomical family of Enterobacteriaceae, become adapted to environmental habitats without losing their virulence to humans. Adaptation to the plant environment would lead to longer persistence in plants, increasing their chances on transmission to humans via consumption of plant-derived food. One of the mechanisms of adaptation to the plant environment in human pathogens, proposed in this paper, is horizontal transfer of genes from different microbial communities present in the arable ecosystem, like the ones originating from soil, animal digestive track systems (manure), water and plants themselves. Genes that would confer better adaptation to the phytosphere might be genes involved in plant colonization, stress resistance and nutrient acquisition and utilization. Because human pathogenic enterics often were prone to genetic exchanges via phages and conjugative plasmids, it was postulated that these genetic elements may be hold key responsible for horizontal gene transfers between human pathogens and indigenous microbes in agroproduction systems. In analogy to zoonosis, we coin the term phytonosis for a human pathogen that is transmitted via plants and not exclusively via animals.

First genome sequences of Achromobacter phages reveal new members of the N4 family

BACKGROUND

Multi-resistant Achromobacter xylosoxidans has been recognized as an emerging pathogen causing nosocomially acquired infections during the last years. Phages as natural opponents could be an alternative to fight such infections. Bacteriophages against this opportunistic pathogen were isolated in a recent study. This study shows a molecular analysis of two podoviruses and reveals first insights into the genomic structure of Achromobacter phages so far.

METHODS

Growth curve experiments and adsorption kinetics were performed for both phages. Adsorption and propagation in cells were visualized by electron microscopy. Both phage genomes were sequenced with the PacBio RS II system based on single molecule, real-time (SMRT) technology and annotated with several bioinformatic tools. To further elucidate the evolutionary relationships between the phage genomes, a phylogenomic analysis was conducted using the genome Blast Distance Phylogeny approach (GBDP).

RESULTS

In this study, we present the first detailed analysis of genome sequences of two Achromobacter phages so far. Phages JWAlpha and JWDelta were isolated from two different waste water treatment plants in Germany. Both phages belong to the Podoviridae and contain linear, double-stranded DNA with a length of 72329 bp and 73659 bp, respectively. 92 and 89 putative open reading frames were identified for JWAlpha and JWDelta, respectively, by bioinformatic analysis with several tools. The genomes have nearly the same organization and could be divided into different clusters for transcription, replication, host interaction, head and tail structure and lysis. Detailed annotation via protein comparisons with BLASTP revealed strong similarities to N4-like phages.

CONCLUSIONS

Analysis of the genomes of Achromobacter phages JWAlpha and JWDelta and comparisons of different gene clusters with other phages revealed that they might be strongly related to other N4-like phages, especially of the Escherichia group. Although all these phages show a highly conserved genomic structure and partially strong similarities at the amino acid level, some differences could be identified. Those differences, e.g. the existence of specific genes for replication or host interaction in some N4-like phages, seem to be interesting targets for further examination of function and specific mechanisms, which might enlighten the mechanism of phage establishment in the host cell after infection.

Scrutinizing virus genome termini by high-throughput sequencing

Analysis of genomic terminal sequences has been a major step in studies on viral DNA replication and packaging mechanisms. However, traditional methods to study genome termini are challenging due to the time-consuming protocols and their inefficiency where critical details are lost easily. Recent advances in next generation sequencing (NGS) have enabled it to be a powerful tool to study genome termini. In this study, using NGS we sequenced one iridovirus genome and twenty phage genomes and confirmed for the first time that the high frequency sequences (HFSs) found in the NGS reads are indeed the terminal sequences of viral genomes. Further, we established a criterion to distinguish the type of termini and the viral packaging mode. We also obtained additional terminal details such as terminal repeats, multi-termini, asymmetric termini. With this approach, we were able to simultaneously detect details of the genome termini as well as obtain the complete sequence of bacteriophage genomes. Theoretically, this application can be further extended to analyze larger and more complicated genomes of plant and animal viruses. This study proposed a novel and efficient method for research on viral replication, packaging, terminase activity, transcription regulation, and metabolism of the host cell.

Phage cocktails and the future of phage therapy

Viruses of bacteria, known as bacteriophages or phages, were discovered nearly 100 years ago. Their potential as antibacterial agents was appreciated almost immediately, with the first 'phage therapy' trials predating Fleming's discovery of penicillin by approximately a decade. In this review, we consider phage therapy that can be used for treating bacterial infections in humans, domestic animals and even biocontrol in foods. Following an overview of the topic, we explore the common practice - both experimental and, in certain regions of the world, clinical - of mixing therapeutic phages into cocktails consisting of multiple virus types. We conclude with a discussion of the commercial and medical context of phage cocktails as therapeutic agents. In comparing off-the-shelf versus custom approaches, we consider the merits of a middle ground, which we deem 'modifiable'. Finally, we explore a regulatory framework for such an approach based on an influenza vaccine model.

The complete genome sequence of EC1-UPM, a novel N4-like bacteriophage that infects Escherichia coli O78:K80

BACKGROUND

Bacteriophage EC1-UPM is an N4-like bacteriophage which specifically infects Escherichia coli O78:K80, an avian pathogenic strain that causes colibacillosis in poultry. The complete genome sequence of bacteriophage EC1-UPM was analysed and compared with other closely related N4-like phage groups to assess their genetic similarities and differences.

RESULTS

Bacteriophage EC1-UPM displays a very similar codon usage profile with its host and does not contain any tRNA gene. Comparative genomics analysis reveals close resemblance of bacteriophage EC1-UPM to three N4-like bacteriophages namely vB_EcoP_G7C, IME11 and KBNP21 with a total of 44 protein coding genes shared at 70% identity threshold. The genomic region coding for the tail fiber protein was found to be unique in bacteriophage EC1-UPM. Further annotation of the tail fiber protein using HHpred, a highly sensitive homology detection tool, reveals the presence of protein structure homologous to various polysaccharide processing proteins in its C-terminus. Leveraging on the availability of multiple N4-like bacteriophage genome sequences, the core genes of N4-like bacteriophages were identified and used to perform a multilocus phylogenetic analysis which enabled the construction of a phylogenetic tree with higher confidence than phylogenetic trees based on single genes.

CONCLUSION

We report for the first time the complete genome sequence of a N4-like bacteriophage which is lytic against avian pathogenic Escherichia coli O78:K80. A novel 928 amino acid residues tail fiber protein was identified in EC1-UPM which may be useful to further the understanding of phage-host specificity. Multilocus phylogenetic analysis using core genes of sequenced N4-like phages showed that the evolutionary relationship correlated well with the pattern of host specificity.

Whole genome sequencing and comparative genomic analyses of two Vibrio cholerae O139 Bengal-specific Podoviruses to other N4-like phages reveal extensive genetic diversity

Background

Vibrio cholerae O139 Bengal is the only serogroup other than O1 implicated in cholera epidemics. We describe the isolation and characterization of an O139 serogroup-specific phage, vB_VchP_VchO139-I (ϕVchO139-I) that has similar host range and virion morphology as phage vB_VchP_JA1 (ϕJA1) described previously. We aimed at a complete molecular characterization of both phages and elucidation of their genetic and structural differences and assessment of their genetic relatedness to the N4-like phage group.

Methods

Host-range analysis and plaque morphology screening were done for both ϕJA1 and ϕVchO139-I. Both phage genomes were sequenced by a 454 and Sanger hybrid approach. Genomes were annotated and protein homologies were determined by Blast and HHPred. Restriction profiles, PFGE patterns and data on the physical genome structure were acquired and phylogenetic analyses were performed.

Results

The host specificity of ϕJA1 has been attributed to the unique capsular O-antigen produced by O139 strains. Plaque morphologies of the two phages were different; ϕVchO139-I produced a larger halo around the plaques than ϕJA1. Restriction profiles of ϕJA1 and ϕVchO139-I genomes were also different. The genomes of ϕJA1 and ϕVchO139-I consisted of linear double-stranded DNA of 71,252 and 70,938 base pairs. The presence of direct terminal repeats of around 1974 base pairs was demonstrated. Whole genome comparison revealed single nucleotide polymorphisms, small insertions/deletions and differences in gene content. Both genomes had 79 predicted protein encoding sequences, of which only 59 were identical between the two closely related phages. They also encoded one tRNA-Arg gene, an intein within the large terminase gene, and four homing endonuclease genes. Whole genome phylogenetic analyses of ϕJA1 and ϕVchO139-I against other sequenced N4-like phages delineate three novel subgroups or clades within this phage family.

Conclusions

The closely related phages feature significant genetic differences, in spite of being morphologically identical. The phage morphology, genetic organization, genomic content and large terminase protein based phylogeny support the placement of these two phages in the Podoviridae family, more specifically within the N4-like phage group. The physical genome structure of ϕJA1 could be demonstrated experimentally. Our data pave the way for potential use of ϕJA1 and ϕVchO139-I in Vibrio cholerae typing and control.

The role of prophage in plant-pathogenic bacteria

A diverse set of phage lineages is associated with the bacterial plant-pathogen genomes sequenced to date. Analysis of 37 genomes revealed 5,169 potential genes (approximately 4.3 Mbp) of phage origin, and at least 50% had no function assigned or are nonessential to phage biology. Some phytopathogens have transcriptionally active prophage genes under conditions that mimic plant infection, suggesting an association between plant disease and prophage transcriptional modulation. The role of prophages within genomes for cell biology varies. For pathogens such as Pectobacterium, Pseudomonas, Ralstonia, and Streptomyces, involvement of prophage in disease symptoms has been demonstrated. In Xylella and Xanthomonas, prophage activity is associated with genome rearrangements and strain differentiation. For other pathogens, prophage roles are yet to be established. This review integrates available information in a unique interface ( http://propnav.esalq.usp.br ) that may be assessed to improve research in prophage biology and its association with genome evolution and pathogenicity.

Klebsiella phage vB_KleM-RaK2 - a giant singleton virus of the family Myoviridae

At 346 kbp in size, the genome of a jumbo bacteriophage vB_KleM-RaK2 (RaK2) is the largest Klebsiella infecting myovirus genome sequenced to date. In total, 272 out of 534 RaK2 ORFs lack detectable database homologues. Based on the similarity to biologically defined proteins and/or MS/MS analysis, 117 of RaK2 ORFs were given a functional annotation, including 28 RaK2 ORFs coding for structural proteins that have no reliable homologues to annotated structural proteins in other organisms. The electron micrographs revealed elaborate spike-like structures on the tail fibers of Rak2, suggesting that this phage is an atypical myovirus. While head and tail proteins of RaK2 are mostly myoviridae-related, the bioinformatics analysis indicate that tail fibers/spikes of this phage are formed from podovirus-like peptides predominantly. Overall, these results provide evidence that bacteriophage RaK2 differs profoundly from previously studied viruses of the Myoviridae family.

Complete genome sequence of IME15, the first T7-like bacteriophage lytic to pan-antibiotic-resistant Stenotrophomonas maltophilia

T7-like bacteriophages are a class of virulent bacteriophages which have a clearer genetic background and smaller genomes than other phages. In addition, it grows faster and is easier to culture than other phages. At present, the numbers of available T7-like bacteriophage genomes and Stenotrophomonas maltophilia genomes are small, and IME15 is the first T7-like virulent Stenotrophomonas phage whose sequence has been reported. It shows effective lysis of S. maltophilia. Here we announce its complete genome, and major findings from its annotation are described.

Complete genome sequence of IME11, a new N4-like bacteriophage

N4-like bacteriophages are a class of virulent Podoviridae phages for which few genome sequences are present in GenBank. IME11, a novel lytic Escherichia bacteriophage with a wide host range, was isolated, and the whole genome was sequenced. It has a circular double-stranded DNA genome of 72,570 bp. Genomic analysis showed that it resembles another Escherichia phage, vB_EcoP_G7C. Here we announce its complete genome and major findings from its annotation.

Long tail fibres of the novel broad-host-range T-even bacteriophage S16 specifically recognize Salmonella OmpC

We report isolation and characterization of the novel T4-like Salmonella bacteriophage vB_SenM-S16. S16 features a T-even morphology and a highly modified 160 kbp dsDNA genome with 36.9 mol % G+C, containing 269 putative coding sequences and three tRNA genes. S16 is a virulent phage, and exhibits a maximally broad host range within the genus Salmonella, but does not infect other bacteria. Synthesis of functional S16 full-length long tail fibre (LTF) in Escherichia coli was possible by coexpression of gp37 and gp38. Surface plasmon resonance analysis revealed nanomolar equilibrium affinity of the LTF to its receptor on Salmonella cells. We show that OmpC serves as primary binding ligand, and that S16 adsorption can be transferred to E. coli by substitution of ompC with the Salmonella homologue. S16 also infects 'rough' Salmonella strains which are defective in lipopolysaccharide synthesis and/or its carbohydrate substitution, indicating that this interaction does not require an intact LPS structure. Altogether, its virulent nature, broad host range and apparent lack of host DNA transduction render S16 highly suitable for biocontrol of Salmonella in foods and animal production. The S16 LTF represents a highly specific affinity reagent useful for cell decoration and labelling, as well as bacterial immobilization and separation.

Erwinia amylovora loop-mediated isothermal amplification (LAMP) assay for rapid pathogen detection and on-site diagnosis of fire blight

Several molecular methods have been developed for the detection of Erwinia amylovora, the causal agent of fire blight in pear and apple, but none are truly applicable for on-site use in the field. We developed a fast, reliable and field applicable detection method using a novel target on the E. amylovora chromosome that we identified by applying a comparative genomic pipeline. The target coding sequences (CDSs) are both uniquely specific for and all-inclusive of E. amylovora genotypes. This avoids potential false negatives that can occur with most commonly used methods based on amplification of plasmid gene targets, which can vary among strains. Loop-mediated isothermal AMPlification (LAMP) with OptiGene Genie II chemistry and instrumentation proved to be an exceptionally rapid (under 15 min) and robust method for detecting E. amylovora in orchards, as well as simple to use in the plant diagnostic laboratory. Comparative validation results using plant samples from inoculated greenhouse trials and from natural field infections (of regional and temporal diverse origin) showed that our LAMP had an equivalent or greater performance regarding sensitivity, specificity, speed and simplicity than real-time PCR (TaqMan), other LAMP assays, immunoassays and plating, demonstrating its utility for routine testing.

Complete genomic sequence of Erwinia amylovora phage PhiEaH2

Erwinia amylovora is the causative agent of fire blight, a serious disease of some Rosaceae plants. The newly isolated bacteriophage PhiEaH2 is able to lyse E. amylovora in the laboratory and has reduced the occurrence of fire blight cases in field experiments. This study presents the sequenced complete genome and analysis of phage PhiEaH2.

Erwinia amylovora CRISPR elements provide new tools for evaluating strain diversity and for microbial source tracking

Clustered regularly interspaced short palindromic repeats (CRISPRs) comprise a family of short DNA repeat sequences that are separated by non repetitive spacer sequences and, in combination with a suite of Cas proteins, are thought to function as an adaptive immune system against invading DNA. The number of CRISPR arrays in a bacterial chromosome is variable, and the content of each array can differ in both repeat number and in the presence or absence of specific spacers. We utilized a comparative sequence analysis of CRISPR arrays of the plant pathogen Erwinia amylovora to uncover previously unknown genetic diversity in this species. A total of 85 E. amylovora strains varying in geographic isolation (North America, Europe, New Zealand, and the Middle East), host range, plasmid content, and streptomycin sensitivity/resistance were evaluated for CRISPR array number and spacer variability. From these strains, 588 unique spacers were identified in the three CRISPR arrays present in E. amylovora, and these arrays could be categorized into 20, 17, and 2 patterns types, respectively. Analysis of the relatedness of spacer content differentiated most apple and pear strains isolated in the eastern U.S. from western U.S. strains. In addition, we identified North American strains that shared CRISPR genotypes with strains isolated on other continents. E. amylovora strains from Rubus and Indian hawthorn contained mostly unique spacers compared to apple and pear strains, while strains from loquat shared 79% of spacers with apple and pear strains. Approximately 23% of the spacers matched known sequences, with 16% targeting plasmids and 5% targeting bacteriophage. The plasmid pEU30, isolated in E. amylovora strains from the western U.S., was targeted by 55 spacers. Lastly, we used spacer patterns and content to determine that streptomycin-resistant strains of E. amylovora from Michigan were low in diversity and matched corresponding streptomycin-sensitive strains from the background population.

Fire blight: applied genomic insights of the pathogen and host

The enterobacterial phytopathogen Erwinia amylovora causes fire blight, an invasive disease that threatens a wide range of commercial and ornamental Rosaceae host plants. The response elicited by E. amylovora in its host during disease development is similar to the hypersensitive reaction that typically leads to resistance in an incompatible host-pathogen interaction, yet no gene-for-gene resistance has been described for this host-pathogen system. Comparative genomic analysis has found an unprecedented degree of genetic uniformity among strains of E. amylovora, suggesting that the pathogen has undergone a recent genetic bottleneck. The genome of apple, an important host of E. amylovora, has been sequenced, creating new opportunities for the study of interactions between host and pathogen during fire blight development and for the identification of resistance genes. This review includes recent advances in the genomics of both host and pathogen.