Prokaryote viruses studied by electron microscopy

This review summarizes the electron microscopical descriptions of prokaryote viruses. Since 1959, nearly 6300 prokaryote viruses have been described morphologically, including 6196 bacterial and 88 archaeal viruses. As in previous counts, the vast majority (96.3 %) are tailed, and only 230 (3.7 %) are polyhedral, filamentous, or pleomorphic. The family Siphoviridae, whose members are characterized by long, noncontractile tails, is by far the largest family (over 3600 descriptions, or 57.3 %). Prokaryote viruses are found in members of 12 bacterial and archaeal phyla. Archaeal viruses belong to 15 families or groups of family level and infect members of 16 archaeal genera, nearly exclusively hyperthermophiles or extreme halophiles. Tailed archaeal viruses are found in the Euryarchaeota only, whereas most filamentous and pleomorphic archaeal viruses occur in the Crenarchaeota. Bacterial viruses belong to 10 families and infect members of 179 bacterial genera, mostly members of the Firmicutes and γ-proteobacteria.

Diversity of Streptococcus thermophilus phages in a large-production cheese factory in Argentina

Phage infections still represent a serious risk to the dairy industry, in which Streptococcus thermophilus is used in starter cultures for the manufacture of yogurt and cheese. The goal of the present study was to analyze the biodiversity of the virulent S. thermophilus phage population in one Argentinean cheese plant. Ten distinct S. thermophilus phages were isolated from cheese whey samples collected in a 2-mo survey. They were then characterized by their morphology, host range, and restriction patterns. These phages were also classified within the 2 main groups of S. thermophilus phages (cos- and pac-type) using a newly adapted multiplex PCR method. Six phages were classified as cos-type phages, whereas the 4 others belonged to the pac-type group. This study illustrates the phage diversity that can be found in one factory that rotates several cultures of S. thermophilus. Limiting the number of starter cultures is likely to reduce phage biodiversity within a fermentation facility.

"phiKZ-like viruses", a proposed new genus of myovirus bacteriophages

The proposed phiKZ genus of myoviruses has 21 members. Phages are virulent, lyse Pseudomonas bacteria, and are characterized by very large heads and correspondingly high DNA contents. The genome of the type virus, phiKZ, has 306 ORFs and over 280 kbp and is the second-largest phage genome known. The phiKZ genus has very few relationships to other phages and includes three species and one possible species.

5500 Phages examined in the electron microscope

"Phages" include viruses of eubacteria and archaea. At least 5568 phages have been examined in the electron microscope since the introduction of negative staining in 1959. Most virions (96%) are tailed. Only 208 phages (3.7%) are polyhedral, filamentous, or pleomorphic. Phages belong to one order, 17 families, and three "floating" groups. Phages are found in 11 eubacterial and archaeal phyla and infect 154 host genera, mostly of the phyla Actinobacteria, Firmicutes, and Proteobacteria. Of the tailed phages, 61% have long, noncontractile tails and belong to the family Siphoviridae. Convergent evolution is visible in the morphology of certain phage groups.

Characterization of a new virulent phage (MLC-A) of Lactobacillus paracasei

A new virulent bacteriophage (MLC-A) was recently isolated in Argentina from a probiotic dairy product containing a strain of Lactobacillus paracasei. Observation of the lysate with an electron microscope revealed bacteriophage particles with an icosahedral capsid of 57 +/- 2 nm; with a collar and a noncontractile tail of 156 +/- 3 nm terminating with a baseplate to which a tail fiber was attached. Therefore, phage MLC-A belongs to the Siphoviridae family. This phage was able to survive the pasteurization process and was resistant to alcohols and sodium hypochlorite (400 mg/kg). Only peracetic acid could inactivate high-titer suspensions of phages in a short time. The maximum rates of phage adsorption to its host cells were obtained at 30 degrees C with a pH between 5 and 7, and in the presence of calcium or magnesium ions. The host range of phage MLC-A encompassed L. paracasei and Lactobacillus casei strains, but it was not able to infect Lactobacillus rhamnosus or Lactobacillus gasseri strains. One-step growth kinetics of its lytic development revealed latent and burst periods of 30 and 135 min, respectively, with a burst size of about 69 +/- 4 plaque-forming units per infected cell. Phage MLC-A had a distinctive restriction profile when compared with the 2 well-studied Lactobacillus phages, PL-1 and J-1. The genome size of the MLC-A phage was estimated to be approximately 37 kb. This study presents the description of the first phage specific for L. paracasei isolated in Argentina. The isolation of phage MLC-A indicates that, beside lactic acid bacteria starters, probiotic cultures can also be sensitive to virulent phages in industrial processes.

Isolation and characterization of Thermus bacteriophages

One-hundred-fifteen bacteriophage strains were isolated from alkaline hot springs in Iceland, New Zealand, Russia (Kamchatka), and the U.S.A. The phages belonged to the Myoviridae, Siphoviridae, Tectiviridae, and Inoviridae families. Over 50% of isolates were isometric or filamentous. One type of siphovirus had giant tails of over 800 nm in length. Phages were further characterized by host range, genome size, DNA restriction endonuclease digestion patterns, and temperature and pH sensitivity. Myoviruses and tectiviruses had a worldwide distribution. Most phages were narrowly host-specific and all were highly resistant against heating and alkaline and acidic pH. This is the first time that tectiviruses and filamentous phages are reported for bacteria of the Thermus-Deinococcus phylum. The presence of tectiviruses, inoviruses, and myoviruses is attributed to acquisition from ancestral gamma-proteobacteria by horizontal gene transfer.

Spontaneous tail length variation in a Salmonella myovirus

Salmonella phage SPT-1, a member of the Myoviridae family and a relative of phage O1, produces abnormally long tails with coordinate variations of sheath and core length. The length of abnormal tails varies between 140 and 445 nm.

Bacteriophage observations and evolution

Bacteriophages are classified into one order and 13 families. Over 5100 phages have been examined in the electron microscope since 1959. At least 4950 phages (96%) are tailed. They constitute the order Caudovirales and three families. Siphoviridae or phages with long, noncontractile tails predominate (61% of tailed phages). Polyhedral, filamentous, and pleomorphic phages comprise less than 4% of bacterial viruses. Bacteriophages occur in over 140 bacterial or archaeal genera. Their distribution reflects their origin and bacterial phylogeny. Bacteriophages are polyphyletic, arose repeatedly in different hosts, and constitute 11 lines of descent. Tailed phages appear as monophyletic and as the oldest known virus group.

Nucleotide sequence of a ssRNA phage from Acinetobacter: kinship to coliphages

The complete nucleotide sequence of ssRNA phage AP205 propagating in Acinetobacter species is reported. The RNA has three large ORFs, which code for the following homologues of the RNA coliphage proteins: the maturation, coat and replicase proteins. Their gene order is the same as that in coliphages. RNA coliphages or Leviviridae fall into two genera: the alloleviviruses, like Q(beta), which have a coat read-through protein, and the leviviruses, like MS2, which do not have this coat protein extension. AP205 has no read-through protein and may therefore be classified as a levivirus. A major digression from the known leviviruses is the apparent absence of a lysis gene in AP205 at the usual position, overlapping the coat and replicase proteins. Instead, two small ORFs are present at the 5' terminus, preceding the maturation gene. One of these might encode a lysis protein. The other is of unknown function. Other new features concern the 3'-terminal sequence. In all ssRNA coliphages, there are always three cytosine residues at the 3' end, but in AP205, there is only a single terminal cytosine. Distantly related viruses, like AP205 and the coliphages, do not have significant sequence identity; yet, important secondary structural features of the RNA are conserved. This is shown here for the 3' UTR and the replicase-operator hairpin. Interestingly, although AP205 has the genetic map of a levivirus, its 3' UTR has the length and RNA secondary structure of an allolevivirus. Sharing features with both MS2 and Q(beta) suggests that, in an evolutionary sense, AP205 should be placed between Q(beta) and MS2. A phylogenetic tree for the ssRNA phages is presented.

Frequency of morphological phage descriptions in the year 2000. Brief review

Over 5100 bacterial viruses have been examined in the electron microscope since 1959. About 4950 phages (96%) are tailed and only 186 phages (3.6%), are cubic, filamentous, or pleomorphic. Phages belong to 13 virus families and occur in over 140 bacterial genera. Phages are listed by morphotypes and host genera. Siphoviridae or phages with long, noncontractile tails comprise 61% of tailed phages. The distribution of phages in different bacterial phylogenetic divisions is shown.

Localization of surface immunogenic protein on group B streptococcus

The localization and accessibility of the group B streptococcus (GBS) surface immunogenic protein (Sip) at the surface of intact GBS cells were studied by flow cytometric assay and immunogold electron microscopy. Antibodies present in pooled sera collected from mice after immunization with purified recombinant Sip efficiently recognized native Sip at the surfaces of the different GBS strains tested, which included representatives of all nine serotypes. Examination of GBS cells by immunogold electron microscopy revealed that the Sip-specific antibodies attached preferentially to polar sites and the septal region. This result confirmed that Sip is exposed at the intact-cell surface, but it also suggests that its distribution is restricted to certain regions of the cell.

Phylogeny of the major head and tail genes of the wide-ranging T4-type bacteriophages

We examined a number of bacteriophages with T4-type morphology that propagate in different genera of enterobacteria, Aeromonas, Burkholderia, and Vibrio. Most of these phages had a prolate icosahedral head, a contractile tail, and a genome size that was similar to that of T4. A few of them had more elongated heads and larger genomes. All these phages are phylogenetically related, since they each had sequences homologous to the capsid gene (gene 23), tail sheath gene (gene 18), and tail tube gene (gene 19) of T4. On the basis of the sequence comparison of their virion genes, the T4-type phages can be classified into three subgroups with increasing divergence from T4: the T-evens, pseudoT-evens, and schizoT-evens. In general, the phages that infect closely related host species have virion genes that are phylogenetically closer to each other than those of phages that infect distantly related hosts. However, some of the phages appear to be chimeras, indicating that, at least occasionally, some genetic shuffling has occurred between the different T4-type subgroups. The compilation of a number of gene 23 sequences reveals a pattern of conserved motifs separated by sequences that differ in the T4-type subgroups. Such variable patches in the gene 23 sequences may determine the size of the virion head and consequently the viral genome length. This sequence analysis provides molecular evidence that phages related to T4 are widespread in the biosphere and diverged from a common ancestor in acquiring the ability to infect different host bacteria and to occupy new ecological niches.

A catalogue of T4-type bacteriophages

The T4-type of bacteriophages is broadly defined on the basis of particle morphology. It occurs in enterobacteria (125 representatives), acinetobacters, aeromonads, pseudomonads, and vibrios (16 isolates). In addition, 18 apparently unrelated phages with prolate heads and contractile tails are found in a wide range of bacteria. A descriptive catalogue of these phages is presented. The T4-type probably originated in precursors of enterobacteria.

Tailed bacteriophages: the order caudovirales

Tailed bacteriophages have a common origin and constitute an order with three families, named Caudovirales. Their structured tail is unique. Tailed phages share a series of high-level taxonomic properties and show many facultative features that are unique or rare in viruses, for example, tail appendages and unusual bases. They share with other viruses, especially herpesviruses, elements of morphogenesis and life-style that are attributed to convergent evolution. Tailed phages present three types of lysogeny, exemplified by phages lambda, Mu, and P1. Lysogeny appears as a secondary property acquired by horizontal gene transfer. Amino acid sequence alignments (notably of DNA polymerases, integrases, and peptidoglycan hydrolases) indicate frequent events of horizontal gene transfer in tailed phages. Common capsid and tail proteins have not been detected. Tailed phages possibly evolved from small protein shells with a few genes sufficient for some basal level of productive infection. This early stage can no longer be traced. At one point, this precursor phage became perfected. Some of its features were perfect enough to be transmitted until today. It is tempting to list major present-day properties of tailed phages in the past tense to construct a tentative history of these viruses: 1. Tailed phages originated in the early Precambrian, long before eukaryotes and their viruses. 2. The ur-tailed phage, already a quite evolved virus, had an icosahedral head of about 60 nm in diameter and a long non-contractile tail with sixfold symmetry. The capsid contained a single molecule of dsDNA of about 50 kb, and the tail was probably provided with a fixation apparatus. Head and tail were held together by a connector. a. The particle contained no lipids, was heavier than most viruses to come, and had a high DNA content proportional to its capsid size (about 50%). b. Most of its DNA coded for structural proteins. Morphopoietic genes clustered at one end of the genome, with head genes preceding tail genes. Lytic enzymes were probably coded for. A part of the phage genome was nonessential and possibly bacterial. Were tailed phages general transductants since the beginning? 3. The virus infected its host from the outside, injecting its DNA. Replication involved transcription in several waves and formation of DNA concatemers. Novel phages were released by burst of the infected cell after lysis of host membranes by a peptidoglycan hydrolase (and a holin?). a. Capsids were assembled from a starting point, the connector, and around a scaffold. They underwent an elaborate maturation process involving protein cleavage and capsid expansion. Heads and tails were assembled separately and joined later. b. The DNA was cut to size and entered preformed capsids by a headful mechanism. 4. Subsequently, tailed phages diversified by: a. Evolving contractile or short tails and elongated heads. b. Exchanging genes or gene fragments with other phages. c. Becoming temperate by acquiring an integrase-excisionase complex, plasmid parts, or transposons. d. Acquiring DNA and RNA polymerases and other replication enzymes. e. Exchanging lysin genes with their hosts. f. Losing the ability to form concatemers as a consequence of acquiring transposons (Mu) or proteinprimed DNA polymerases (phi 29). Present-day tailed phages appear as chimeras, but their monophyletic origin is still inscribed in their morphology, genome structure, and replication strategy. It may also be evident in the three-dimensional structure of capsid and tail proteins. It is unlikely to be found in amino acid sequences because constitutive proteins must be so old that relationships were obliterated and most or all replication-, lysogeny-, and lysis-related proteins appear to have been borrowed. However, the sum of tailed phage properties and behavior is so characteristic that tailed phages cannot be confused with other viruses.

Taxonomic changes in tailed phages of enterobacteria

Out of 136 new phages, 80 (59%) are classified into 23 species according to morphology and physicochemical properties. Six new species are described and species beta 4, from a previous classification scheme, is renamed T1. The morphology of 36 phage species is schematically represented.

Frequency of morphological phage descriptions in 1995

At least 4500 bacterial viruses have been examined in the electron microscope since 1959. About 4400 phages (96%) are tailed and only 162 phages (4%) are cubic, filamentous, or pleomorphic. Phages belong to 12 virus families and occur in about 130 bacterial genera. Phages are listed by morphotypes and host genera. Siphoviridae or phages with long, noncontractile tails include about 60% of tailed phages.

Phage typing of Bacillus subtilis and B. thuringiensis

Phage typing schemes for Bacillus subtilis and B. thuringiensis were constructed using 98 phages and 743 bacterial strains. Most phages were host-species-specific. Phages were classified by electron microscopy. The B. subtilis scheme includes 10 phages and 29 phage types. The B. thuringiensis scheme comprises 8 phages and 25 phage types and can be applied to B. cereus. There is no correlation between H antigen serotypes and phagovars in B. thuringiensis. Characteristics of typing phages are described for identity control.

Bacillus cereus phage typing as an epidemiological tool in outbreaks of food poisoning

Bacillus cereus is responsible for an increasing number of food poisoning cases. By using 12 bacteriophages isolated from sewage, a typing scheme for B. cereus isolates from outbreaks or sporadic cases of food poisoning was developed. The phages belonged to three morphotypes. Ten phages with contractile tails and icosahedral heads were members of the Myoviridae family, and two phages with noncontractile tails belonged to the Siphoviridae family. Phage 11 represented a new species. It had an isometric head and a very long contractile tail with long wavy tail fibers and was one of the largest viruses known. The vast majority of 166 B. cereus strains (161, or 97%) isolated from food poisoning cases were typeable. Of 146 strains isolated from 18 outbreaks, 142 (97%) could be divided into 17 phage types. A good correlation, on the order of 80 to 100%, between phage types of strains isolated from suspected foods and those of strains isolated from stools of symptomatic patients was observed. Most Bacillus thuringiensis strains were also typeable, providing further evidence of the close relatedness of B. cereus and B. thuringiensis. This phage typing scheme can be a valuable epidemiological tool in tracing the origins of food poisoning caused by B. cereus.

Classification of Acinetobacter phages

Eight phage species and type viruses are proposed. They belong to the Myoviridae, Siphoviridae, and Podoviridae families of tailed phages and are characterized by a combination of morphological and physicochemical properties. An unusual siphovirus species has an elongated head and transverse tail disks.

New Bacillus bacteriophage species

Nine new species of tailed Bacillus phages, based on morphological and physicochemical properties, are defined. Phage P10 is one of the largest viruses known. The total number of tailed Bacillus phage species is presently 33.

Bacteriophages from Bombyx mori

Preparations of silkworm larvae contained two large phages with contractile tails (Myoviridae). One phage was active on Pseudomonas paucimobilis. The other, not cultivated, was one of the largest viruses known.

PID, a new member of the P1 bacteriophage group

Phage P1D produces particles of essentially uniform head size and differs from P1 in its range and tail length. The dimensions of phage P1 are reassessed. The P1 phage group shows signs of morphological evolution.

Biological inactivation of adhering Listeria monocytogenes by listeriaphages and a quaternary ammonium compound

The use of listeriaphages as a means of disinfecting contaminated stainless-steel and polypropylene surfaces was investigated. Surfaces artificially contaminated with L. monocytogenes 10401 and 8427 were sanitized with suspensions of listeriaphages (H387, H387-A, and 2671), all belonging to the Siphoviridae family. Phage suspensions at concentrations of up to 3.5 x 10(8) PFU/ml were at least as efficient as a 20 ppm solution of a quaternary ammonium compound (QUATAL) in reducing L. monocytogenes populations. A synergistic activity was observed when two or more phages were used in combination and when phages were suspended in QUATAL. The biological activity of the three phages was not affected by QUATAL concentrations of 50 ppm and a contact time of 4 h.

[The human gastroenteritis virus in the Quebec region (1986-1991). Identification by electronic microscopy]

Between 1986 and 1991, 251 fecal samples were examined. Viruses were found in 48% of stools, namely adenoviruses, astroviruses, caliciviruses, coronaviruses, rotaviruses, and particles reassembling the Norwalk agent (74% of positive cases). All morphological types of viruses normally associated with human gastroenteritis are present in Quebec, its vicinity, and in the east of the Province. The interpretation of specimens is complicated by the presence of a wide variety of biological structures including bacteriophages. Electron microscopy is the method of choice for identification of the whole range of gastroenteritis viruses.

A study of five bacteriophages of the Myoviridae family which replicate on different gram-positive bacteria

A comparative study is reported on five phages of the Myoviridae family which propagate on Bacillus subtilis, B. thuringiensis, Enterococcus sp., Lactobacillus plantarum, or Staphylococcus aureus. The phages are morphologically identical and characterized by isometric heads with conspicuous capsomers and by contractile tails with complex base plates. The phages show similar protein profiles, but vary considerably in burst size. Phage DNAs are about 95-166 kb in size and are unrelated by DNA-DNA hybridization and restriction endonuclease analysis. Therefore the phages are unrelated at species level. Implications of these data for our understanding of the development of phage species are discussed.

Morphology of phages of a general Salmonella typing set

The typing set includes 27 tailed phages belonging to three families, the Myoviridae (contractile tails, 4 phages), Siphoviridae (long, non-contractile tails, 21 phages) and Podoviridae (short tails, 2 phages). Heads are isometric or elongated. The phages fall into 10 morphological groups, seven of which correspond to known enterobacterial phage species (Jersey, N4, T5, T7, ZG/3a, chi, 16-19) and one to a Rhizobium phage species (CM1). T5-type and T7-type phages are for the first time reported in salmonellae. Two phages produce large amounts of abnormal mottled heads.

Frequency of morphological phage descriptions

Bacteriophages are listed by morphotypes and host genera. At least 4.007 phages, belonging to 13 virus families, have been described since 1960. About 3,850 phages (96%) are tailed and 154 phages (4%) are cubic, filamentous, or pleomorphic. Siphoviridae or phages with long noncontractile tails constitute 60% of tailed phages. Phages are found in over 100 bacterial genera including archaebacteria and rickettsiae. Their distribution is very uneven and probably reflects the evolutionary history of bacteria.

The species concept and its application to tailed phages

A recently proposed polythetic definition of virus species appears easily applicable to bacteriophages. Criteria for classification of tailed phages are evaluated. Morphology, DNA homology, and serology are the most important criteria for delineation of species, but no single criterion is satisfactory. Dot-blot hybridization and seroneutralization may suggest false relationships by detecting common sequences in the DNA of otherwise unrelated phages. Species of tailed phages can be defined by a combination of morphology and DNA homology or serology. A procedure for identification of novel phages is outlined. Phage names should include elements of host names.

Characteristics and diffusion in the rabbit of a phage for Escherichia coli 0103. Attempts to use this phage for therapy

A bacteriophage for Escherichia coli 0103 was isolated during a study on E. coli diarrhoea in intensive breeding units of rabbits. The phage had an isometric head and a short tail and resembled coliphage N4 (Podoviridae). It had a very narrow host range and seemed to be specific for serogroup 0103, suggesting that it might be used for preliminary identification of E. coli strains of this serogroup instead of the usual slide agglutination. In view of its possible use as a therapeutic phage, we investigated its dissemination in rabbit organs after oral administration. The phage persisted in the spleen for at least 12 days. However, in vivo studies showed that this phage and a mixture of more virulent phages for E. coli 0103 were ineffective in preventing disease in rabbits inoculated with an enteropathogenic strain of E. coli 0103.

Large-scale blood substitute production using a microfluidizer

Microfluidization has been tested as a way to disperse phospholipids in aqueous hemoglobin solutions. Spherical and stable liposomes of 2 to 3 microns were obtained. Lipid incorporation (up to 85%) and hemoglobin encapsulation (up to 15%) in liposomes have been improved with respect to previous investigations. However, results show that a more efficient dispersion system using lower concentrations of lipid is required to obtain a high liposome hemoglobin concentration (limited actually to 150 g/l) and an economically and biologically suitable process for artificial blood production at large scale.

Morphology of Staphylococcus saprophyticus bacteriophages

The morphology of 6 bacteriophages isolated from Staphylococcus saprophyticus was studied by electron microscopy. Phages had isometric heads and non-contractile tails, thus belonging to the Siphoviridae family. They were subdivided into two morphological groups based on head diameter and tail length. Type I, represented by phages 1154A and 1405, and characterized by an unusually small capsid, may be a new species.

A new bacteriophage of Corynebacterium glutamicum isolated from swine waste

A bacteriophage for Corynebacterium glutamicum strain LP-6 was isolated from swine waste. It belongs to the Siphoviridae family or Bradley morphologic group B, has a narrow host range, and is sensitive to chloroform and resistant to carbon tetrachloride. The phage is unstable (96% inactivation) in swine waste stored for 4 months at 22 C. The DNA has a molecular weight of approximately 20 Md, cohesive ends, and numerous restriction endonuclease sites. The phage differs from other known C glutamicum phages.

Morphology of Pseudomonas aeruginosa typing phages of the Lindberg set

Eighteen phages were studied by electron microscopy. They belonged to eight morphotypes representing the Myoviridae, Siphoviridae and Podoviridae families of tailed phages. Twelve phages were members of known species and six phages belonged to three new species. Results correlated closely with serological and DNA-DNA hybridization data. Induced and non-induced propagating bacteria were investigated for lysogeny. All strains produced R-type pyocins, phage-like particles or inhibitory reactions. The identity of typing phages should be controlled periodically.

Bacteriophage taxonomy in 1987

Ten families and eight genera have been approved by the International Committee on Taxonomy of Viruses (ICTV) and include at least 230 species. A new basic phage group has been found in Archaebacteria. Over 2700 phages are tailed; about 130 are cubic, filamentous or pleomorphic. Their distribution provides insights into phage origin.

New actinophage species

All actinophages of known morphology are tailed. From 305 phages surveyed, 4 belong to the Myoviridae family, 283 to the Siphoviridae, and 18 to the Podoviridae (two morphotypes each). 58 of 139 actinophages described since 1976 are classified in this report, and the earlier phage descriptions are updated. Nine new species and type viruses are proposed, bringing the total number of actinophage species to 29 and the number of bacterial host genera to 15.

Morphology of Pasteurella multocida bacteriophages

Twenty-one tailed phages with icosahedral heads belong to the Myoviridae, Siphoviridae, and Podoviridae families and to four morphological types. Type AU, with 10 phages, has a contractile tail and is morphologically identical with coliphage P2. Lysates contain contracted tail sheaths assembled end-to-end and abnormal structures with long tails and multiple tail sheaths. Types C-2 and 32, with one and three phages, respectively, have long, noncontractile tails. Type 22 includes seven phages, has a short tail, and resembles coliphage T7. Our results agree with previous biological data and suggest that types AU, C-2, 32, and 22 correspond to four different phage species.

New species definitions in phages of gram-positive cocci

About 290 phages of the bacterial genera Leuconostoc, Micrococcus, Staphylococcus, and Streptococcus were surveyed. The phages belong to the Myoviridae, Siphoviridae, and Podoviridae families and comprise seven basic morphotypes. Fourteen new species are proposed, bringing the number of phage species for gram-positive cocci to 27. The distribution of particular phage types may indicate phylogenetic relationships between host bacteria.

Classification of Vibrio bacteriophages

85 Vibrio phages, 84 of them tailed and 1 filamentous, were surveyed. The tailed phages belonged to six basic morphotypes and to the Myoviridae, Siphoviridae, or Podoviridae families. 63 phages were classified into 18 species. The filamentous phage is a member of the Inovirus genus of the Inoviridae family. Vibrio phages are very heterogenous and include some morphologically interesting viruses. Several Vibrio phages closely resemble phages of other gram-negative bacteria, possibly indicating phylogenetic relationships between their hosts.

Six groups of double-stranded RNA mycoviruses

Six groups of double-stranded (ds) RNA mycoviruses have been proposed. The main characteristics which define a group are described, and the properties of members and probable members of each group are tabulated. Possibilities for organization of the groups into families, genera and species are discussed. The classification scheme could ultimately accommodate the majority of the well-characterized dsRNA mycoviruses.

Sewage coliphages studied by electron microscopy

Sewage was enriched with 35 Escherichia coli strains, and sediments of enrichment cultures were studied in the electron microscope. They contained up to 10 varieties of morphologically different particles. T-even-type phages predominated in 14 samples. Thirteen phages were enriched, representing the families Myoviridae (seven), Styloviridae (two), Podoviridae (three), and Microviridae (one). Twelve of these corresponded to known enterobacterial phage species, namely, 121, K19, FC3-9, O1, 9266, T2, 16-19, kappa, beta 4, N4, T7, and phi X174. Cubic RNA phages and filamentous phages were not detected. Types 121 and 9266 have previously been observed only in Romania and South Africa. Identification by morphology is usually simple. Our investigative technique is qualitative and will not detect all phages present. Most enrichment strains are polyvalent, and electron microscopy is always required for phage identification. In a general way, electron microscopy seems to be the method of choice for investigation of phage geography and ecology.

DNA base composition, nature of intracellular DNA, morphology, and classification of bacteriophages infecting Micrococcus luteus

Ten bacteriophages infecting Micrococcus luteus have been characterized. All phages contain double-stranded DNA, of 64.3--73.5 mol% guanine plus cytosine (GC). The DNA of phage N7 has the highest GC content reported for any bacterial virus. No unusual bases have been found. The intracellular replicating DNAs of six phages are covalently closed circular molecules. All 10 phages have isometric, probably icosahedral, heads and long, flexible, noncontractile tails and can be sorted into two morphological groups based on size and presence or absence of a collar. Host-range studies indicate six host-range groups.

Characterization of two Salmonella newport bacteriophages

Salmonella newport phages 16--19 and 7--11 have very long heads and are members of two rare and so far little-known phage groups. Both produce various morphological aberrations. Preparations of phage 7--11 contain numerous polyheads and about 0.4% short heads belonging to nine size classes. In addition, one giant phage particle was observed. The head of phage 7--11 seems to be an icosahedron which became elongated by adding successive rows of subunits. Phages 16--19 and 7--11 have buoyant densities in CsCl of 1.43 and 1.48 g/mL and particle weights of 103 and 204 x 10(6) respectively. Both viruses contain double-stranded DNA, internal proteins, and sugars. Phage 16--19 contains 46.5% DNA of 35 x 10(6) molecular weight, and glucose. Phage 7--11 contains 47.5% DNA of 108 x 10(6) molecular weight, and mannose. Base compositions of phage and S. newport DNAs were determined from buoyant densities, melting point, and acid hydrolysis. Phage 16--19 contains 5.4% 5-methylcytosine.

Bacteriophage-like particles associated with a spirochete

A lysed Treponema bacterium containing cubic phage-like particles, approximately 40nm in diameter, has been observed by negative staining electron microscopy.