Grey wolf genomic history reveals a dual ancestry of dogs.

The grey wolf (Canis lupus) was the first species to give rise to a domestic population, and they remained widespread throughout the last Ice Age when many other large mammal species went extinct. Little is known, however, about the history and possible extinction of past wolf populations or when and where the wolf progenitors of the present-day dog lineage (Canis familiaris) lived1-8. Here we analysed 72 ancient wolf genomes spanning the last 100,000 years from Europe, Siberia and North America. We found that wolf populations were highly connected throughout the Late Pleistocene, with levels of differentiation an order of magnitude lower than they are today. This population connectivity allowed us to detect natural selection across the time series, including rapid fixation of mutations in the gene IFT88 40,000-30,000 years ago. We show that dogs are overall more closely related to ancient wolves from eastern Eurasia than to those from western Eurasia, suggesting a domestication process in the east. However, we also found that dogs in the Near East and Africa derive up to half of their ancestry from a distinct population related to modern southwest Eurasian wolves, reflecting either an independent domestication process or admixture from local wolves. None of the analysed ancient wolf genomes is a direct match for either of these dog ancestries, meaning that the exact progenitor populations remain to be located.

Ophiodimyces ophiodiicola, Etiologic Agent of Snake Fungal Disease, in Europe since Late 1950s.

The fungus Ophiodimyces ophiodiicola is the etiologic agent of snake fungal disease. Recent findings date US occurrence at least as far back as 1945. We analyzed 22 free-ranging snakes with gross lesions consistent with snake fungal disease from museum collections from Europe. We found 5 positive samples, the oldest collected in 1959.

Host Range, Morphology and Sequence Analysis of Ten Temperate Phages Isolated from Pathogenic Yersinia enterocolitica Strains.

Yersinia enterocolitica is a heterogeneous species comprising highly pathogenic, weakly pathogenic and non-pathogenic strains. Previous data suggest that gene exchange may occur in Yersinia. Only scarce information exists about temperate phages of Y. enterocolitica, even though many prophage sequences are present in this species. We have examined 102 pathogenic Y. enterocolitica strains for the presence of inducible prophages by mitomycin C treatment. Ten phages were isolated from nine strains belonging to the bio (B)/serotypes (O) B2/O:5,27, B2/O:9 and 1B/O:8. All phages are myoviruses showing lytic activity only at room temperature. Whole-genome sequencing of the phage genomes revealed that they belong to three groups, which, however, are not closely related to known phages. Group 1 is composed of five phages (type phage: vB_YenM_06.16.1) with genome sizes of 43.8 to 44.9 kb, whereas the four group 2 phages (type phage: vB_YenM_06.16.2) possess smaller genomes of 29.5 to 33.2 kb. Group 3 contains only one phage (vB_YenM_42.18) whose genome has a size of 36.5 kb, which is moderately similar to group 2. The host range of the phages differed significantly. While group 1 phages almost exclusively lysed strains of B2/O:5,27, phages of group 2 and 3 were additionally able to lyse B4/O:3, and some of them even B2/O:9 and 1B/O:8 strains.

Unexpectedly high levels of lineage diversity in Sundaland puddle frogs (Dicroglossidae: Occidozyga Kuhl and van Hasselt, 1822).

One of the most urgent contemporary tasks for taxonomists and evolutionary biologists is to estimate the number of species on earth. Recording alpha diversity is crucial for protecting biodiversity, especially in areas of elevated species richness, which coincide geographically with increased anthropogenic environmental pressures - the world's so-called biodiversity hotspots. Although the distribution of Puddle frogs of the genus Occidozyga in South and Southeast Asia includes five biodiversity hotspots, the available data on phylogeny, species diversity, and biogeography are surprisingly patchy. Samples analyzed in this study were collected throughout Southeast Asia, with a primary focus on Sundaland and the Philippines. A mitochondrial gene region comprising ~ 2000 bp of 12S and 16S rRNA with intervening tRNA Valine and three nuclear loci (BDNF, NTF3, POMC) were analyzed to obtain a robust, time-calibrated phylogenetic hypothesis. We found a surprisingly high level of genetic diversity within Occidozyga, based on uncorrected p-distance values corroborated by species delimitation analyses. This extensive genetic diversity revealed 29 evolutionary lineages, defined by the > 5% uncorrected p-distance criterion for the 16S rRNA gene, suggesting that species diversity in this clade of phenotypically homogeneous forms probably has been underestimated. The comparison with results of other anuran groups leads to the assumption that anuran species diversity could still be substantially underestimated in Southeast Asia in general. Many genetically divergent lineages of frogs are phenotypically similar, indicating a tendency towards extensive morphological conservatism. We present a biogeographic reconstruction of the colonization of Sundaland and nearby islands which, together with our temporal framework, suggests that lineage diversification centered on the landmasses of the northern Sunda Shelf. This remarkably genetically structured group of amphibians could represent an exceptional case for future studies of geographical structure and diversification in a widespread anuran clade spanning some of the most pronounced geographical barriers on the planet (e.g., Wallace's Line). Studies considering gene flow, morphology, ecological and bioacoustic data are needed to answer these questions and to test whether observed diversity of Puddle frog lineages warrants taxonomic recognition.

Properties of Two Broad Host Range Phages of Yersinia enterocolitica Isolated from Wild Animals.

Yersinia (Y.) enterocolitica and Y. pseudotuberculosis are important zoonotic agents which can infect both humans and animals. To combat these pathogens, the application of strictly lytic phages may be a promising tool. Since only few Yersinia phages have been described yet, some of which demonstrated a high specificity for certain serotypes, we isolated two phages from game animals and characterized them in terms of their morphology, host specificity, lytic activity on two bio-/serotypes and genome composition. The T7-related podovirus vB_YenP_Rambo and the myovirus vB_YenM_P281, which is very similar to a previously described phage PY100, showed a broad host range. Together, they lysed all the 62 tested pathogenic Y. enterocolitica strains belonging to the most important bio-/serotypes in Europe. A cocktail containing these two phages strongly reduced cultures of a bio-/serotype B4/O:3 and a B2/O:9 strain, even at very low MOIs (multiplicity of infection) and different temperatures, though, lysis of bio-/serotype B2/O:9 by vB_YenM_P281 and also by the related phage PY100 only occurred at 37 °C. Both phages were additionally able to lyse various Y. pseudotuberculosis strains at 28 °C and 37 °C, but only when the growth medium was supplemented with calcium and magnesium cations.

Yersinia pseudotuberculosis Prevalence and Diversity in Wild Boars in Northeast Germany.

In this study, the prevalence of Yersinia pseudotuberculosis in wild boars in northeast Germany was determined. For that purpose, the tonsils of 503 wild boars were sampled. The presence of Y. pseudotuberculosis was studied by diagnostic PCR. Positive samples were analyzed by cultural detection using a modified cold enrichment protocol. Ten Y. pseudotuberculosis isolates were obtained, which were characterized by biotyping, molecular serotyping, and multilocus sequence typing (MLST). In addition, whole-genome sequences and the antimicrobial susceptibility of the isolates were analyzed. Yersinia pseudotuberculosis was isolated from male and female animals, most of which were younger than 1 year. A prevalence of 2% (10/503) was determined by cultural detection, while 6.4% (32/503) of the animals were positive by PCR. The isolates belonged to the biotypes 1 and 2 and serotypes O:1a (n = 7), O:1b (n = 2), and O:4a (n = 1). MLST analysis revealed three sequence types, ST9, ST23, and ST42. Except one isolate, all isolates revealed a strong resistance to colistin. The relationship of the isolates was studied by whole-genome sequencing demonstrating that they belonged to four clades, exhibiting five different pulsed-field gel electrophoresis (PFGE) restriction patterns and a diverse composition of virulence genes. Six isolates harbored the virulence plasmid pYV. Besides two isolates, all isolates contained ail and inv genes and a complete or incomplete high-pathogenicity island (HPI). None of them possessed a gene for the superantigen YPM. The study shows that various Y. pseudotuberculosis strains exist in wild boars in northeast Germany, which may pose a risk to humans.IMPORTANCEYersinia pseudotuberculosis is a foodborne pathogen whose occurrence is poorly understood. One reason for this situation is the difficulty in isolating the species. The methods developed for the isolation of Yersinia enterocolitica are not well suited for Y. pseudotuberculosis We therefore designed a protocol which enabled the isolation of Y. pseudotuberculosis from a relatively high proportion of PCR-positive wild boar tonsils. The study indicates that wild boars in northeast Germany may carry a variety of Y. pseudotuberculosis strains, which differ in terms of their pathogenic potential and other properties. Since wild boars are widely distributed in German forests and even populate cities such as Berlin, they may transmit yersiniae to other animals and crop plants and may thus cause human infections through the consumption of contaminated food. Therefore, the prevalence of Y. pseudotuberculosis should be determined also in other animals and regions to learn more about the natural reservoir of this species.

Campylobacter group II phage CP21 is the prototype of a new subgroup revealing a distinct modular genome organization and host specificity.

BACKGROUND: The application of phages is a promising tool to reduce the number of Campylobacter along the food chain. Besides the efficacy against a broad range of strains, phages have to be safe in terms of their genomes. Thus far, no genes with pathogenic potential (e.g., genes encoding virulence factors) have been detected in Campylobacter phages. However, preliminary studies suggested that the genomes of group II phages may be diverse and prone to genomic rearrangements. RESULTS: We determined and analysed the genomic sequence (182,761 bp) of group II phage CP21 that is closely related to the already characterized group II phages CP220 and CPt10. The genomes of these phages are comprised of four modules separated by very similar repeat regions, some of which harbouring open reading frames (ORFs). Though, the arrangement of the modules and the location of some ORFs on the genomes are different in CP21 and in CP220/CPt10. In this work, a PCR system was established to study the modular genome organization of other group II phages demonstrating that they belong to different subgroups of the CP220-like virus genus, the prototypes of which are CP21 and CP220. The subgroups revealed different restriction patterns and, interestingly enough, also distinct host specificities, tail fiber proteins and tRNA genes. We additionally analysed the genome of group II phage vB_CcoM-IBB_35 (IBB_35) for which to date only five individual contigs could be determined. We show that the contigs represent modules linked by long repeat regions enclosing some yet not identified ORFs (e.g., for a head completion protein). The data suggest that IBB_35 is a member of the CP220 subgroup. CONCLUSION: Campylobacter group II phages are diverse regarding their genome organization. Since all hitherto characterized group II phages contain numerous genes for transposases and homing endonucleases as well as similar repeat regions, it cannot be excluded that these phages are genetically unstable. To answer this question, further experiments and sequencing of more group II phages should be performed.

PVv3, a new shuttle vector for gene expression in Vibrio vulnificus.

An efficient electroporation procedure for Vibrio vulnificus was designed using the new cloning vector pVv3 (3,107 bp). Transformation efficiencies up to 2 × 10(6) transformants per µg DNA were achieved. The vector stably replicated in both V. vulnificus and Escherichia coli and was also successfully introduced into Vibrio parahaemolyticus and Vibrio cholerae. To demonstrate the suitability of the vector for molecular cloning, the green fluorescent protein (GFP) gene and the vvhBA hemolysin operon were inserted into the vector and functionally expressed in Vibrio and E. coli.

A suggested classification for two groups of Campylobacter myoviruses.

Most Campylobacter bacteriophages isolated to date have long contractile tails and belong to the family Myoviridae. Based on their morphology, genome size and endonuclease restriction profile, Campylobacter phages were originally divided into three groups. The recent genome sequencing of seven virulent campylophages reveal further details of the relationships between these phages at the genome organization level. This article details the morphological and genomic features among the campylophages, investigates their taxonomic position, and proposes the creation of two new genera, the "Cp220likevirus" and "Cp8unalikevirus" within a proposed subfamily, the "Eucampyvirinae"

Dressed in black. A New Ansonia Stoliczka, 1870 (Lissamphibia: Anura: Bufonidae) from Gunung Murud, Sarawak, East Malaysia (Borneo).

A new species of stream toad of the genus Ansonia is described from Gunung Murud, Pulong Tau National Park, of northern Sarawak, Malaysia, Borneo. Ansonia vidua, sp. nov., is morphologically distinguished from its Bornean congeners by the following combination of characters: medium size (SVL of adult females 33.5-34.4 mm); body uniformly black-brown in life; absence of a visible pattern on dorsum or limbs; presence of two low interorbital ridges; shagreened skin on dorsum, sides and upper surfaces of the limbs with numerous homogeneously small, rounded warts; first finger shorter than second; reduced webbing between the toes and an absence of a sharp tarsal ridge. Uncorrected genetic distances between related taxa of > 4.3% in 16S rRNA gene support its status as a hitherto undescribed species.

Red hot chili pepper. A new Calluella stoliczka, 1872 (Lissamphibia: Anura: Microhylidae) from Sarawak, East Malaysia (Borneo).

A new brightly-coloured (olive and red) species of microhylid frog of the genus Calluella Stoliczka 1872 is described from the upper elevations of Gunung Penrissen and the Matang Range, Sarawak, East Malaysia (Borneo). Calluella capsa, new species, is diagnosable in showing the following combination of characters: SVL up to 36.0 mm; dorsum weakly granular; a faint dermal fold across forehead; toe tips obtuse; webbing on toes basal; lateral fringes on toes present; outer metatarsal tubercle present; and dorsum greyish-olive, with red spots; half of venter bright red, the rest with large white and dark areas. The new species is the eighth species of Calluella to be described, and the fourth known from Borneo. A preliminary phylogeny of Calluella and its relatives is presented, and the new taxon compared with congeners from Malaysia and other parts of south-east Asia. 

A bacteriophage cocktail can efficiently reduce five important Salmonella serotypes both on chicken skin and stainless steel.

Salmonella is one of the most important zoonotic pathogens and is mostly transmitted through food of animal origin. Application of bacteriophages is a promising tool to biocontrol Salmonella on both food and food contact surfaces. In this study, we evaluated the effectiveness of a six-phage cocktail for the reduction of Salmonella Enteritidis and a mixture of five major Salmonella serotypes (S. Enteritidis, Salmonella Typhimurium, Salmonella Infantis, Salmonella Paratyphi B, and Salmonella Indiana) on chicken skin and stainless steel. A phage cocktail with a final concentration of 107 PFU/cm2 was sprayed on these surfaces. After adding the phage cocktail, the samples were incubated at RT (~23°C) for different periods of time. The phage cocktail caused a significant reduction of S. Enteritidis and the mixed culture on chicken skin 30 min after phage addition, with 1.8 log10 and 1 log10 units, respectively. Reduction rates (1.2-1.7 log10 units) on stainless steel after 30 min were similar. Four hours after addition, the phage cocktail caused a significant reduction on both surfaces up to 3 log10 units on chicken skin and 2.4 log10 units on stainless steel. In a further experiment, bacteria added to stainless steel were not allowed to dry to simulate a fresh bacterial contamination. In this case, the bacterial count of S. Enteritidis was reduced below the detection limit after 2 h. The results demonstrate that this phage cocktail has potential to be used in post-harvest applications to control Salmonella contaminations.

Genetic identification, morphology and distribution of Natrixhelvetica subspecies in southern and western Switzerland (Reptilia, Squamata, Serpentes).

Most of Switzerland is inhabited by the nominotypical subspecies of the barred grass snake (Natrixhelveticahelvetica), which is characterized by mitochondrial DNA lineage E. Only in the northeast of the country, the common grass snake (N.natrix) occurs and hybridizes with N.h.helvetica in a narrow contact zone. However, we discovered that in southern and western Switzerland barred grass snakes representing another mtDNA lineage (lineage C) are widely distributed. Lineage C is typical for Alpine populations of the southern subspecies N.h.sicula. Our microsatellite analyses of the Swiss samples revealed differences between the two subspecies and also a substructure with two clusters in each subspecies. Furthermore, we discovered a contact and hybrid zone of N.h.helvetica and N.h.sicula along the northern shore of Lake Geneva and also confirm that interbreeding with alien common grass snakes (N.n.moreotica, mtDNA lineage 7) occurs there. This finding is of concern for nature conservation and measures should be taken to prevent further genetic pollution. Using morphometrics, we found no differences between the two subspecies of N.helvetica, while N.natrix was slightly distinct from N.helvetica.

Biological and genomic characterization of three psychrophilic Y. enterocolitica phages.

Yersinia (Y.) enterocolitica is an important foodborne pathogenic species that is mainly transmitted by the consumption of contaminated meat, particularly pork. To combat the bacteria along the food chain, the application of strictly lytic phages may be a promising tool. As the temperatures in the gut of animals and during food processing can differ significantly, a phage cocktail intended to be used for applications should comprise phages that are active at various temperatures. In this study, we isolated and characterized three phages with a myoviridal morphology (vB_YenM_P8, vB_YenM_P744 and vB_YenM_P778), which lysed the most important Y. enterocolitica serotypes O:3, O:9 and O:5,27 at a low multiplicity of infection (MOI) and at low temperatures down to 6°C. While vB_YenM_P8 is a member of the T4 family, vB_YenM_P744 and vB_YenM_P778 are novel phages that do not show relationship to known phages. The three phages were mixed in a cocktail with the already described phages vB_YenM_P281 and vB_YenP_Rambo. The cocktail revealed a strong lytic activity and lysed a mixture of Y. enterocolitica serotypes at room temperature (RT) within few hours with a reduction of up to 4.8 log10 units. Moreover, at even lower temperatures the mixture was significantly reduced after incubation overnight. The strongest reductions were determined at 6°C (4.0 log10 units) suggesting that the cocktail can lyse the psychrophilic Y. enterocolitica also during food processing. To determine possible phage resistance, 100 colonies that survived the infection by the phages were isolated and analysed regarding their serotype and phage susceptibility. Most isolates belonged to serotype O:9, but all of them were still sensitive to at least one phage of the cocktail.

The complete genome sequence of bacteriophage CP21 reveals modular shuffling in Campylobacter group II phages.

Campylobacter group II phages described so far share a high degree of sequence similarity. We report the 182,833-bp genomic sequence of the closely related group II phage CP21 and show that it has a completely different genomic organization. As in other group II phages, the CP21 genome is composed of large modules separated by long DNA repeat regions which obviously trigger recombination and modular shuffling.

Diversification in a biodiversity hotspot--the evolution of Southeast Asian rhacophorid tree frogs on Borneo (Amphibia: Anura: Rhacophoridae).

The tree-frog family Rhacophoridae is a major group contributing to the high pecies richness and reproductive diversity among vertebrates of Sundaland. Nonetheless, rhacophorid evolution, specially on Borneo, has not been studied within a phylogenetic context. In this study, we examine the phylogenetic relationships of 38 (out of 41) Bornean species of Rhacophoridae, in combination with data from previous phylogenetic studies. In the final super matrix of 91 species, we analyse sequence data from two mitochondrial and three nuclear genes. The resulting trees show the genus Rhacophorus as a paraphyletic assemblage. As a consequence, we transfer Rhacophorus appendiculatus and R. kajau to two other genera and propose the new phylogeny-based combinations--Kurixalus appendiculatus and Feihyla kajau, respectively. Furthermore, we use our phylogenetic hypotheses to reconstruct the evolution of reproductive modes in rhacophorid tree frogs. Direct development to the exclusion of a free larval stage evolved twice independently, once in an ancestor of the Pseudophilautus+Raorchestes clade in India and Sri Lanka, and once within Philautus in Southeast Asia. The deposition of egg clutches covered by a layer of jelly in Feihyla is also present in F. kajau and thus confirms our generic reassignment. The remarkably high diversity of rhacophorid tree frogs on Borneo is the outcome of a complex pattern of repeated vicariance and dispersal events caused by past changes in the climatic and geological history of the Sunda shelf. We identified geographic clades of closely related endemic species within Rhacophorus and Philautus, which result from local island radiations on Borneo.

Isolation and characterization of phages with lytic activity against methicillin-resistant Staphylococcus aureus strains belonging to clonal complex 398.

Some years ago, MRSA clonal complex (CC) 398 emerged, which spread extensively in livestock animals. People in contact with food production animals are at high risk of colonization. A reduction of MRSA CC398 in livestock might be achieved by application of virulent phages. However, there have not yet been any reports published on phages lysing MRSA CC398 strains. In this study, three virulent phages (PSa1, PSa2 and PSa3) with lytic activity against MRSA CC398 strains were isolated from German pig farms. Morphologically, the phages are members of the family Podoviridae, and they exhibited an identical host range. They lysed 52 (60 %) out of 86 tested MRSA CC398 strains representing 18 different spa types. While the PSa1 and PSa3 genomes have a similar size of approximately 17.5 kb, the PSa2 genome is somewhat larger (ca. 18.5 kb). Southern hybridization revealed strong DNA homologies between the phages, which was confirmed by sequence analysis of cloned restriction fragments and PCR products. Moreover, the whole PSa3 genomic sequence (17,602 bp) showed a close relationship to 44AHJD-like phages, which are not known to contain virulence-associated genes. To assess whether these phages might be candidates for applications, in vitro experiments were carried out in which the number of MRSA CC398 cells could be reduced by up to four log10 units. The phages were stable at a wide range of temperatures and pH values.

A Bacteriophage Cocktail Reduces Five Relevant Salmonella Serotypes at Low Multiplicities of Infection and Low Temperatures.

Salmonella are important pathogenic bacteria and, following Campylobacter, they are the second most common cause of bacterial foodborne infections worldwide. To reduce the presence of bacteria along the food chain, the application of bacteriophages (phages) may be a promising tool. In this study, the lytic properties of six phages against five relevant Salmonella serotypes (S. Enteritidis, S. Typhimurium, S. Infantis, S. Paratyphi B and S. Indiana) were analyzed. Three phages were able to lyse all five serotypes. We determined the lytic potential of each phage on indicator strains in vitro at room temperature (RT) and at 37 °C using low multiplicities of infection (MOIs). Most phages reduced their host more efficiently at RT than at 37 °C, even at the lowest MOI of 0.001. Following this, the lytic activity of a cocktail comprising five phages (MOI = 0.1) was examined with each of the five serotypes and a mix of them at RT, 15, 12, 10, 8 and 6 °C. All cultures of single serotypes as well as the mixture of strains were significantly reduced at temperatures as low as 8 °C. For single serotypes, reductions of up to 5 log10 units and up to 2.3 log10 units were determined after 6 h (RT) and 40 h (8 °C), respectively. The mixture of strains was reduced by 1.7 log10 units at 8 °C. The data clearly suggest that these phages are suitable candidates for biocontrol of various Salmonella serotypes under food manufacturing conditions.

The Novel Yersinia enterocolitica Telomere Phage vB_YenS_P840 Is Closely Related to PY54, but Reveals Some Striking Differences.

Telomere phages are a small group of temperate phages, whose prophages replicate as a linear plasmid with covalently closed ends. They have been isolated from some Enterobacteriaceae and from bacterial species living in aquatic environments. Phage PY54 was the first Yersinia (Y.) enterocolitica telomere phage isolated from a nonpathogenic O:5 strain, but recently a second telomeric Yersinia phage (vB_YenS_P840) was isolated from a tonsil of a wild boar in Germany. Both PY54 and vB_YenS_P840 (P840) have a siphoviridal morphology and a similar genome organization including the primary immunity region immB and telomere resolution site telRL. However, whereas PY54 only possesses one prophage repressor for the lysogenic cycle, vB_YenS_P840 encodes two. The telRL region of this phage was shown to be processed by the PY54 protelomerase under in vivo conditions, but unlike with PY54, a flanking inverted repeat was not required for processing. A further substantial difference between the phages is their host specificity. While PY54 infects Y. enterocolitica strains belonging to the serotypes O:5 and O:5,27, vB_YenS_P840 exclusively lyses O:3 strains. As the tail fiber and tail fiber assembly proteins of the phages differ significantly, we introduced the corresponding genes of vB_YenS_P840 by transposon mutagenesis into the PY54 genome and isolated several mutants that were able to infect both serotypes, O:5,27 and O:3.

Campylobacter jejuni group III phage CP81 contains many T4-like genes without belonging to the T4-type phage group: implications for the evolution of T4 phages.

CP81 is a virulent Campylobacter group III phage whose linear genome comprises 132,454 bp. At the nucleotide level, CP81 differs from other phages. However, a number of its structural and replication/recombination proteins revealed a relationship to the group II Campylobacter phages CP220/CPt10 and to T4-type phages. Unlike the T4-related phages, the CP81 genome does not contain conserved replication and virion modules. Instead, the respective genes are scattered throughout the phage genome. Moreover, most genes for metabolic enzymes of CP220/CPt10 are lacking in CP81. On the other hand, the CP81 genome contains nine similar genes for homing endonucleases which may be involved in the attrition of the conserved gene order for the virion core genes of T4-type phages. The phage apparently possesses an unusual modification of C or G bases. Efficient cleavage of its DNA was only achieved with restriction enzymes recognizing pure A/T sites. Uncommonly, phenol extraction leads to a significant loss of CP81 DNA from the aqueous layer, a property not yet described for other phages belonging to the T4 superfamily.