Isolation of the Novel Phage PHB09 and Its Potential Use against the Plant Pathogen Pseudomonas syringae pv. actinidiae

Bacteriophages are viruses that specifically infect target bacteria. Recently, bacteriophages have been considered potential biological control agents for bacterial pathogens due to their host specificity. Pseudomonas syringae pv. actinidiae (Psa) is a reemerging pathogen that causes bacterial canker of kiwifruit (Actinidia sp.). The economic impact of this pest and the development of resistance to antibiotics and copper sprays in Psa and other pathovars have led to investigation of alternative management strategies. Phage therapy may be a useful alternative to conventional treatments for controlling Psa infections. Although the efficacy of bacteriophage φ6 was evaluated for the control of Psa, the characteristics of other DNA bacteriophages infecting Psa remain unclear. In this study, the PHB09 lytic bacteriophage specific to Psa was isolated from kiwifruit orchard soil. Extensive host range testing using Psa isolated from kiwifruit orchards and other Pseudomonas strains showed PHB09 has a narrow host range. It remained stable over a wide range of temperatures (4-50 °C) and pH values (pH 3-11) and maintained stability for 50 min under ultraviolet irradiation. Complete genome sequence analysis indicated PHB09 might belong to a new myovirus genus in Caudoviricetes. Its genome contains a total of 94,844 bp and 186 predicted genes associated with phage structure, packaging, host lysis, DNA manipulation, transcription, and additional functions. The isolation and identification of PHB09 enrich the research on Pseudomonas phages and provide a promising biocontrol agent against kiwifruit bacterial canker.

Phage Biocontrol of Pseudomonas aeruginosa in Water

Bacteriophage control of harmful or pathogenic bacteria has aroused growing interest, largely due to the rise of antibiotic resistance. The objective of this study was to test phages as potential agents for the biocontrol of an opportunistic pathogen Pseudomonas aeruginosa in water. Two P. aeruginosa bacteriophages (vB_PaeM_V523 and vB_PaeM_V524) were isolated from wastewater and characterized physically and functionally. Genomic and morphological characterization showed that both were myoviruses within the Pbunavirus genus. Both had a similar latent period (50-55 min) and burst size (124-134 PFU/infected cell), whereas there was variation in the host range. In addition to these environmental phages, a commercial Pseudomonas phage, JG003 (DSM 19870), was also used in the biocontrol experiments. The biocontrol potential of the three phages in water was tested separately and together as a cocktail against two P. aeruginosa strains; PAO1 and the environmental strain 17V1507. With PAO1, all phages initially reduced the numbers of the bacterial host, with phage V523 being the most efficient (>2.4 log10 reduction). For the environmental P. aeruginosa strain (17V1507), only the phage JG003 caused a reduction (1.2 log10) compared to the control. The cocktail of three phages showed a slightly higher decrease in the level of the hosts compared to the use of individual phages. Although no synergistic effect was observed in the host reduction with the use of the phage cocktail, the cocktail-treated hosts did not appear to acquire resistance as rapidly as hosts treated with a single phage. The results of this study provide a significant step in the development of bacteriophage preparations for the control of pathogens and harmful microbes in water environments.

Designing P. aeruginosa synthetic phages with reduced genomes

In the era where antibiotic resistance is considered one of the major worldwide concerns, bacteriophages have emerged as a promising therapeutic approach to deal with this problem. Genetically engineered bacteriophages can enable enhanced anti-bacterial functionalities, but require cloning additional genes into the phage genomes, which might be challenging due to the DNA encapsulation capacity of a phage. To tackle this issue, we designed and assembled for the first time synthetic phages with smaller genomes by knocking out up to 48% of the genes encoding hypothetical proteins from the genome of the newly isolated Pseudomonas aeruginosa phage vB_PaeP_PE3. The antibacterial efficacy of the wild-type and the synthetic phages was assessed in vitro as well as in vivo using a Galleria mellonella infection model. Overall, both in vitro and in vivo studies revealed that the knock-outs made in phage genome do not impair the antibacterial properties of the synthetic phages, indicating that this could be a good strategy to clear space from phage genomes in order to enable the introduction of other genes of interest that can potentiate the future treatment of P. aeruginosa infections.

Phage phiKZ-The First of Giants

The paper covers the history of the discovery and description of phiKZ, the first known giant bacteriophage active on Pseudomonas aeruginosa. It also describes its unique features, especially the characteristic manner of DNA packing in the head around a cylinder-shaped structure ("inner body"), which probably governs an ordered and tight packaging of the phage genome. Important properties of phiKZ-like phages include a wide range of lytic activity and the blue opalescence of their negative colonies, and provide a background for the search and discovery of new P. aeruginosa giant phages. The importance of the phiKZ species and of other giant phage species in practical phage therapy is noted given their broad use in commercial phage preparations.

Spatial structure affects phage efficacy in infecting dual-strain biofilms of Pseudomonas aeruginosa

Bacterial viruses, or phage, are key members of natural microbial communities. Yet much research on bacterial-phage interactions has been conducted in liquid cultures involving single bacterial strains. Here we explored how bacterial diversity affects the success of lytic phage in structured communities. We infected a sensitive Pseudomonas aeruginosa strain PAO1 with a lytic phage Pseudomonas 352 in the presence versus absence of an insensitive P. aeruginosa strain PA14, in liquid culture versus colonies on agar. We found that both in liquid and in colonies, inter-strain competition reduced resistance evolution in the susceptible strain and decreased phage population size. However, while all sensitive bacteria died in liquid, bacteria in colonies could remain sensitive yet escape phage infection, due mainly to reduced growth in colony centers. In sum, spatial structure can protect bacteria against phage infection, while the presence of competing strains reduces the evolution of resistance to phage.

Characterization of Two Pseudomonas aeruginosa Viruses vB_PaeM_SCUT-S1 and vB_PaeM_SCUT-S2

The sophisticated antibiotic resistance mechanism of Pseudomonas aeruginosa has urged the development of alternative antibacterial strategies. Phage therapy has been proven successful for the treatment of multidrug-resistant infections. In this study, we reported two virulent P. aeruginosa phages, vB_PaeM_SCUT-S1 (S1) and vB_PaeM_SCUT-S2 (S2), which were characterized at morphological, genomic, and proteomic levels. Phages S1 and S2 were assigned to the Myoviridae family. The genome sequencing showed that the genome size of Phage S1 was 66,046 bp and that of Phage S2 was 94,434 bp. The phylogenetic tree indicated that the two phages were distantly related to each other and were classified in the genera Pbunavirus and Pakpunavirus respectively. Thirty-one proteins were identified for each phage by mass spectrometry and were used to substantiate the function of the predicted coding genes. The two phages inhibited the growth of P. aeruginosa strain PAO1 at low multiplicity of infection levels and had good performance both on preventing biofilm formation and eradicating preformed biofilms. They were also stable over a wide range of temperature and pH values, supporting their potential use in the treatment of P. aeruginosa infections.

Large Preferred Region for Packaging of Bacterial DNA by phiC725A, a Novel Pseudomonas aeruginosa F116-Like Bacteriophage

Bacteriophage vB_PaeP_PAO1_phiC725A (short name phiC725A) was isolated following mitomycin C induction of C7-25, a clinical Pseudomonas aeruginosa strain carrying phiC725A as a prophage. The phiC725A genome sequence shows similarity to F116, a P. aeruginosa podovirus capable of generalized transduction. Likewise, phiC725A is a podovirus with long tail fibers. PhiC725A was able to lysogenize two additional P. aeruginosa strains in which it was maintained both as a prophage and in an episomal state. Investigation by deep sequencing showed that bacterial DNA carried inside phage particles originated predominantly from a 700-800kb region, immediately flanking the attL prophage insertion site, whether the phages were induced from a lysogen or recovered after infection. This indicates that during productive replication, recombination of phage genomes with the bacterial chromosome at the att site occurs occasionally, allowing packaging of adjacent bacterial DNA.

[Genetic and molecular principles for the selection of Pseudomonas and Staphylococcus therapeutic bacteriophages]

The content of empirically selected bacteriophage mixtures, produced by Microgen for the prevention and treatment of staphylococcal and pseudomonade infections, was investigated by negative stain electron microscopy. The main population of phages was shown to belong to the groups suitable for therapeutic purposes based on bioinformatics analysis of known genomes of Pseudomonas and Staphylococcus phages. However, the phage morphology studies did not always reveal the exact correspondence of the phage to the exact group. Therefore, we suggest group genotyping of the therapeutic bacteriophages on thebasis of genetic conservative locus.

Identification of bacteriophages for biocontrol of the kiwifruit canker phytopathogen Pseudomonas syringae pv. actinidiae

Pseudomonas syringae pv. actinidiae is a reemerging pathogen which causes bacterial canker of kiwifruit (Actinidia sp.). Since 2008, a global outbreak of P. syringae pv. actinidiae has occurred, and in 2010 this pathogen was detected in New Zealand. The economic impact and the development of resistance in P. syringae pv. actinidiae and other pathovars against antibiotics and copper sprays have led to a search for alternative management strategies. We isolated 275 phages, 258 of which were active against P. syringae pv. actinidiae. Extensive host range testing on P. syringae pv. actinidiae, other pseudomonads, and bacteria isolated from kiwifruit orchards showed that most phages have a narrow host range. Twenty-four were analyzed by electron microscopy, pulse-field gel electrophoresis, and restriction digestion. Their suitability for biocontrol was tested by assessing stability and the absence of lysogeny and transduction. A detailed host range was performed, phage-resistant bacteria were isolated, and resistance to other phages was examined. The phages belonged to the Caudovirales and were analyzed based on morphology and genome size, which showed them to be representatives of Myoviridae, Podoviridae, and Siphoviridae. Twenty-one Myoviridae members have similar morphologies and genome sizes yet differ in restriction patterns, host range, and resistance, indicating a closely related group. Nine of these Myoviridae members were sequenced, and each was unique. The most closely related sequenced phages were a group infecting Pseudomonas aeruginosa and characterized by phages JG004 and PAK_P1. In summary, this study reports the isolation and characterization of P. syringae pv. actinidiae phages and provides a framework for the intelligent formulation of phage biocontrol agents against kiwifruit bacterial canker.

A giant Pseudomonas phage from Poland

A novel giant phage of the family Myoviridae is described. Pseudomonas phage PA5oct was isolated from a sewage sample from an irrigated field near Wroclaw, Poland. The virion morphology indicates that PA5oct differs from known giant phages. The phage has a head of about 131 nm in diameter and a tail of 136 × 19 nm. Phage PA5oct contains a genome of approximately 375 kbp and differs in size from any tailed phages known. PA5oct was further characterized by determination of its latent period and burst size and its sensitivity to heating, chloroform, and pH.

Plate tectonics of virus shell assembly and reorganization in phage φ8, a distant relative of mammalian reoviruses

The hallmark of a virus is its capsid, which harbors the viral genome and is formed from protein subunits, which assemble following precise geometric rules. dsRNA viruses use an unusual protein multiplicity (120 copies) to form their closed capsids. We have determined the atomic structure of the capsid protein (P1) from the dsRNA cystovirus Φ8. In the crystal P1 forms pentamers, very similar in shape to facets of empty procapsids, suggesting an unexpected assembly pathway that proceeds via a pentameric intermediate. Unlike the elongated proteins used by dsRNA mammalian reoviruses, P1 has a compact trapezoid-like shape and a distinct arrangement in the shell, with two near-identical conformers in nonequivalent structural environments. Nevertheless, structural similarity with the analogous protein from the mammalian viruses suggests a common ancestor. The unusual shape of the molecule may facilitate dramatic capsid expansion during phage maturation, allowing P1 to switch interaction interfaces to provide capsid plasticity.

Genomic and proteomic analyses of the terminally redundant genome of the Pseudomonas aeruginosa phage PaP1: establishment of genus PaP1-like phages

We isolated and characterized a new Pseudomonas aeruginosa myovirus named PaP1. The morphology of this phage was visualized by electron microscopy and its genome sequence and ends were determined. Finally, genomic and proteomic analyses were performed. PaP1 has an icosahedral head with an apex diameter of 68–70 nm and a contractile tail with a length of 138–140 nm. The PaP1 genome is a linear dsDNA molecule containing 91,715 base pairs (bp) with a G+C content of 49.36% and 12 tRNA genes. A strategy to identify the genome ends of PaP1 was designed. The genome has a 1190 bp terminal redundancy. PaP1 has 157 open reading frames (ORFs). Of these, 143 proteins are homologs of known proteins, but only 38 could be functionally identified. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and high-performance liquid chromatography-mass spectrometry allowed identification of 12 ORFs as structural protein coding genes within the PaP1 genome. Comparative genomic analysis indicated that the Pseudomonas aeruginosa phage PaP1, JG004, PAK_P1 and vB_PaeM_C2-10_Ab1 share great similarity. Besides their similar biological characteristics, the phages contain 123 core genes and have very close phylogenetic relationships, which distinguish them from other known phage genera. We therefore propose that these four phages be classified as PaP1-like phages, a new phage genus of Myoviridae that infects Pseudomonas aeruginosa.

Isolation and characterization of a T7-like lytic phage for Pseudomonas fluorescens

BACKGROUND

Despite the proven relevance of Pseudomonas fluorescens as a spoilage microorganism in milk, fresh meats and refrigerated food products and the recognized potential of bacteriophages as sanitation agents, so far no phages specific for P. fluorescens isolates from dairy industry have been closely characterized in view of their lytic efficiency. Here we describe the isolation and characterization of a lytic phage capable to infect a variety of P. fluorescens strains isolated from Portuguese and United States dairy industries.

RESULTS

Several phages were isolated which showed a different host spectrum and efficiency of lysis. One of the phages, phage phiIBB-PF7A, was studied in detail due to its efficient lysis of a wide spectrum of P. fluorescens strains and ribotypes. Phage phiIBB-PF7A with a head diameter of about 63 nm and a tail size of about 13 x 8 nm belongs morphologically to the Podoviridae family and resembles a typical T7-like phage, as analyzed by transmission electron microscopy (TEM). The phage growth cycle with a detected latent period of 15 min, an eclipse period of 10 min, a burst size of 153 plaque forming units per infected cell, its genome size of approximately 42 kbp, and the size and N-terminal sequence of one of the protein bands, which gave similarity to the major capsid protein 10A, are consistent with this classification.

CONCLUSION

The isolated T7-like phage, phage phiIBB-PF7A, is fast and efficient in lysing different P. fluorescens strains and may be a good candidate to be used as a sanitation agent to control the prevalence of spoilage causing P. fluorescens strains in dairy and food related environments.

Cryo-EM Study of the Pseudomonas Bacteriophage φKZ

The phiKZ virus is one of the largest known bacteriophages. It infects Pseudomonas aeruginosa, which is frequently pathogenic in humans, and, therefore, has potential for phage therapy. The phiKZ virion consists of an approximately 1450 A diameter icosahedral head and an approximately 2000 A long contractile tail. The structure of the phiKZ tail has been determined using cryo-electron microscopy. The phiKZ tail is much longer than that of bacteriophage T4. However, the helical parameters of their contractile sheaths, surrounding their tail tubes, are comparable. Although there is no recognizable sequence similarity between the phiKZ and T4 tail sheath proteins, they are similar in size and shape, suggesting that they evolved from a common ancestor. The phiKZ baseplate is significantly larger than that of T4 and has a flatter shape. Nevertheless, phiKZ, similar to T4, has a cell-puncturing device in the middle of its baseplate.

"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.

Genomic analysis of Pseudomonas aeruginosa phages LKD16 and LKA1: establishment of the phiKMV subgroup within the T7 supergroup

Lytic Pseudomonas aeruginosa phages LKD16 and LKA1 were locally isolated and morphologically classified as Podoviridae. While LKD16 adsorbs weakly to its host, LKA1 shows efficient adsorption (ka = 3.9 x 10(-9) ml min(-1)). LKA1, however, displays a narrow host range on clinical P. aeruginosa strains compared to LKD16. Genome analysis of LKD16 (43,200 bp) and LKA1 (41,593 bp) revealed that both phages have linear double-stranded DNA genomes with direct terminal repeats of 428 and 298 bp and encode 54 and 56 genes, respectively. The majority of the predicted structural proteins were experimentally confirmed as part of the phage particle using mass spectrometry. Phage LKD16 is closely related to bacteriophage phiKMV (83% overall DNA homology), allowing a more thoughtful gene annotation of both genomes. In contrast, LKA1 is more distantly related, lacking significant DNA homology and showing protein similarity to phiKMV in 48% of its gene products. The early region of the LKA1 genome has diverged strongly from phiKMV and LKD16, and intriguing differences in tail fiber genes of LKD16 and LKA1 likely reflect the observed discrepancy in infection-related properties. Nonetheless, general genome organization is clearly conserved among phiKMV, LKD16, and LKA1. The three phages carry a single-subunit RNA polymerase gene adjacent to the structural genome region, a feature which distinguishes them from other members of the T7 supergroup. Therefore, we propose that phiKMV represents an independent and widespread group of lytic P. aeruginosa phages within the T7 supergroup.

[Comparison of new giant bacteriophages OBP and Lu11 of soil pseudomonads with bacteriophages of phiKZ-supergroup of Pseudomonas aeruginosa]

Study of two recently isolated giant bacteriophages Lu11 and OBP that are active on Pseudomonas putida var. Manila and Pseudomonas fluorescens, respectively, demonstrated their similarity in morphology, genome size, and size of phage particles, with giant bacteriophages of Pseudomonas aeruginosa assigned to the supergroup of phiKZ-like phages of the family Myoviridae designated in this manner according to the best studied phage phiKZ that belongs to the species of this group widely distributed in nature. Comparison of major polypeptide sizes of mature particles suggests the similarity of certain proteins in the phages examined. In OBP particles visualized with an electron microscope, an "inner body" was detected, which points to the specific DNA package intrinsic to phages of phiKZ group. In the meantime, phages Lul11 and OBP do not exhibit resemblance among themselves or with any of earlier described phiKZ-like phages in respect to other traits; particularly, they have no detectable DNA homology. Note that phage Lu11 of P. putida var. Manila exhibits very slight homology with phage Lin68 of the family of P. aeruginosa phiKZ-like phages detected only in blot hybridization. This suggests the possible involvement of these phages in interspecies recombination ("gene shuffling") between phages of various bacterial species. Results of partial sequencing of phage genomes confirmed the phylogenetic relatedness of phage OBP to phages of the phiKZ-supergroup, whereas phage Lu11 most probably belongs to a novel species that is not a member of supergroup phiKZ composition. The results of the study are discussed in terms of the evolution of these phages.

Genome Comparison of Pseudomonas aeruginosa Large Phages

Pseudomonas aeruginosa phage EL is a dsDNA phage related to the giant phiKZ-like Myoviridae. The EL genome sequence comprises 211,215 bp and has 201 predicted open reading frames (ORFs). The EL genome does not share DNA sequence homology with other viruses and micro-organisms sequenced to date. However, one-third of the predicted EL gene products (gps) shares similarity (Blast alignments of 17-55% amino acid identity) with phiKZ proteins. Comparative EL and phiKZ genomics reveals that these giant phages are an example of substantially diverged genetic mosaics. Based on the position of similar EL and phiKZ predicted gene products, five genome regions can be delineated in EL, four of which are relatively conserved between EL and phiKZ. Region IV, a 17.7 kb genome region with 28 predicted ORFs, is unique to EL. Fourteen EL ORFs have been assigned a putative function based on protein similarity. Assigned proteins are involved in DNA replication and nucleotide metabolism (NAD+-dependent DNA ligase, ribonuclease HI, helicase, thymidylate kinase), host lysis and particle structure. EL-gp146 is the first chaperonin GroEL sequence identified in a viral genome. Besides a putative transposase, EL harbours predicted mobile endonucleases related to H-N-H and LAGLIDADG homing endonucleases associated with group I intron and intein intervening sequences.

A three-dimensional cryo-electron microscopy structure of the bacteriophage phiKZ head

The three-dimensional structure of the Pseudomonas aeruginosa bacteriophage phiKZ head has been determined by cryo-electron microscopy and image reconstruction to 18A resolution. The head has icosahedral symmetry measuring 1455 A in diameter along 5-fold axes and a unique portal vertex to which is attached an approximately 1800 A-long contractile tail. The 65 kDa major capsid protein, gp120, is organized into a surface lattice of hexamers, with T = 27 triangulation. The shape and size of the hexamers is similar to the hexameric building blocks of the bacteriophages T4, phi29, P22, and HK97. Pentameric vertices of the capsid are occupied by complexes composed of several special vertex proteins. The double-stranded genomic DNA is packaged into a highly condensed series of layers, separated by 24 A, that follow the contour of the inner wall of the capsid.

Effects of Virion and Salt Concentrations on the Raman Signatures of Filamentous Phages fd, Pf1, Pf3, and PH75

Filamentous phages consist of a single-stranded DNA genome encapsidated by several thousand copies of a small alpha-helical coat protein subunit plus several copies of four minor proteins at the filament ends. The filamentous phages are important as cloning vectors, vehicles for peptide display, and substrates for macromolecular alignment. Effective use of a filamentous phage in such applications requires an understanding of experimental factors that may influence the propensity of viral filaments to laterally aggregate in solution. Because the Raman spectrum of a filamentous phage is strongly dependent on the relative orientation of the virion with respect to the polarization direction of the electromagnetic radiation employed to excite the spectrum, we have applied Raman spectroscopy to investigate lateral aggregation of phages fd, Pf1, Pf3, and PH75 in solution. The results show that lateral aggregation of the virions and anisotropic orientation of the aggregates are both disfavored by high concentrations of salt (>200 mM NaCl) in solutions containing a relatively low virion concentration (<10 mg/mL). Conversely, the formation of lateral aggregates and their anisotropic orientation are strongly favored by a low salt concentration (<0.1 mM NaCl), irrespective of the virion concentration over a wide range. The use of Raman polarization effects to distinguish isotropic and anisotropic solutions of filamentous phages is consistent with previously reported Raman analyses of virion structures in both solutions and fibers. The Raman data are supported by electron micrographs of negatively stained specimens of phage fd, which permit an independent assessment of salt effects on lateral aggregation. The present results also identify new Raman bands that serve as potential markers of subunit side-chain orientations in filamentous virus assemblies.

[Comparison of genomes of new gigantic Pseudomonas aeruginosa phages from native populations from different regions]

To study the genome diversity of bacteriophages from geographically distant natural populations, new giant phi KZ-like Pseudomonas aeruginosa phages isolated in two different regions were compared with earlier known phages of three species (phi KZ, Lin68, EL). A broad spectrum of lytic activity was demonstrated for all phi KZ-like phages. Phages of the phi KZ species proved to be common in natural populations of various regions, while IL- and Lin68-related phages were extremely rare. Most phi KZ-related phages had unique DNA restriction patterns, but the differences between these were only minor, and the genomes did not contain nonhomologous fragments. The spectrum of capsid polypeptides proved to be conserved in each species, and was proposed as a character necessary and sufficient for express classification of phages with an accuracy of species. Phages isolated in different geographical regions showed no substantial difference. Some phages only slightly differing in DNA restriction pattern from phi KZ may be used to study the origin of phi KZ genes coding for orthologs of proteins of unrelated species (other phages, pathogenic bacteria, eukaryotes).

Myoviridae bacteriophages of Pseudomonas aeruginosa: a long and complex evolutionary pathway

Recently we have accomplished the entire DNA sequence of bacteriophage phiKZ, a giant virus infecting Pseudomonas aeruginosa. The 280334-bp of phiKZ genome is a linear, circularly permutated and terminally redundant, AT-rich dsDNA molecule that contains no sites for NotI, PstI, SacI, SmaI, XhoI and XmaIII endonucleases. Limited homology to other bacteriophages on the DNA and protein levels indicated that phiKZ represents a distinct branch of the Myoviridae family. In this work, we analyzed a group of six P. aeruginosa phages (Lin68, Lin21, PTB80, NN, EL, and RU), which are morphologically similar to phiKZ, have similar genome size and low G+C content. All phages have a broad host range among P. aeruginosa strains, and they are resistant to the inhibitory action of many P. aeruginosa plasmids. The analysis of the genomic DNA by restriction enzymes and DNA-DNA hybridization shows that phages are representative of three phiKZ-like species: phiKZ-type (phiKZ, Lin21, NN and PTB80), EL-type (EL and RU) and Lin68 which has a shorter tail than other phages. Except for related phages EL and RU, all phiKZ-like phages have identical N-terminal amino acid sequences of the major capsid protein. Random genome sequencing shows that the EL and RU phages have no homology to the phiKZ-like phages on DNA level. We propose that the phiKZ, Lin21, NN, PTB80 and Lin68 phages can be included in a new phiKZ genus, and that the EL and RU phages belong to a separate genus within the Myoviridae family. Based on the resistance to many restriction enzymes and the transduction ability, there are indications that over the long pathway of evolution, the phiKZ-like phages probably inherited the capacity to infect different bacterial species.

[Autoplaque formation in a Pseudomonas fluorescens strain: phage-like particles and transactivation of the defective phage]

Natural bacteriophages of Pseudomonas fluorescens are rare and its temperate phages have not been described so far. In search for these phages, we have found that one of the P. fluorescens strains forms numerous small transparent autoplaques of different size and shape, which contained material reproducible on the same strains. When centrifuged in a cesium chloride gradient, this material yielded a band in the density zone of about 1.3 g/cm3, where protein components or bacteriophages with a relatively low content of nucleic acid are usually located. In the band material, electron microscopy revealed phagelike particles with empty and mostly undamaged heads and tails carrying in their distal region a formation resembling contracted sheath. DNA isolated from the preparation consisted of two components: a distinct 54-kb fragment, and a diffuse fragment ranging in size from 20 to 9.5 kb. Treatment of the large DNA fragment with various endonucleases yielded 42.2- and 29.5-kb fragments (on average for different endonucleases); whereas the same treatment of the diffuse fragment yielded two- to three distinct fragments with the overall molecular sizes of 8.9 and 6.2 kb (for different nucleases). We have suggested that cells harbor two different genetic elements whose interaction results in the autoplaque appearance and in the formation of negative colonies after infection with the autoplaque material. One of the two elements displays properties of a defective prophage with disturbed DNA synthesis and assembly, whereas the other exhibits the properties of a transposable phage. After complementation or some other interaction between these elements (transactivation, prophage induction caused by repressor inactivation), a bulk of defective phage particles devoid of DNA and a few DNA-containing particles were produced. It remains unclear whether both DNA types are contained in the same or different particles. The phage (or a system of elements) referred to as PT3 is noninducible. The phage mutants forming larger negative colonies (NCs) were also revealed. Some of bacterial mutants resistant to PT3 infection produce the mutant phage with small and turbid NCs. PT3 produces no NCs on the lawns of other strains of the same or other pseudomonade species. This is the first case of describing a natural temperate bacteriophage in P. fluorescens. The two different elements of this phage may represent the same genome of the defective prophage divided into two portions within a bacterial chromosome, each of which is capable of packaging into the phage head.

Electron microscopic study of DNA packing in phi(kz) bacteriophage (Pseudomonas Aeruginosa) irradiated with laser in the presence of a dye

DNA packing of bacteriophage phikz (Pseudomonas aeruginosa) was studied by electron microscopy after gentle destruction of the capsid with powerful laser impulse in aqueous virus suspension in the presence organic dye. Suspension of destroyed phage heads contained complexes of genomic DNA with endogenous capsid proteins characterized by pronounced regular structure. The type of these structures corresponds to one the main model of phage DNA packing, the so-called coil packing.

Atomic force microscopy analysis of bacteriophages phiKZ and T4

Bacteriophage phiKZ was investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The well-known phage T4 was used as a reference sample. Reproducible contact mode AFM images of native and partially disintegrated particles of bacteriophage phiKZ in air were obtained. It was demonstrated that the heads of phiKZ and T4 phages were compressed differently and depended on adsorption onto highly ordered pyrolytic graphite and mica. We have established a procedure to partially disintegrate the viral particles after which the internal protein body, which is a helical structure with a cylinder-like form, was easily observable inside the bacteriophage phiKZ head.

Structure determination of bacteriophage PP7 from Pseudomonas aeruginosa: from poor data to a good map

The structure of bacteriophage PP7 from Pseudomomas aeruginosa was determined to 3.7 A resolution. Triclinic crystals of three forms were obtained, diffracting to between 4.5 and 3.4 A resolution. The quality of the crystals was exceptionally poor, leading to problems in the evaluation of the recorded images and to a final data set which would appear to be useless with standard criteria for protein crystals. In all crystal forms, the unit cell contains two icosahedral particles, providing 120-fold non-crystallographic symmetry. For two of the crystal forms, the particle orientations were calculated using the self-rotation function. The two particles in the asymmetric unit had very similar but distinct orientations. The position of the second particle was found using the Patterson function. Initial phases to 15 A resolution were calculated using the related phage MS2 as a model. Real-space averaging was performed and phases were extended from 15 A resolution to the limit of the data. The map was improved significantly by using only the 'high' resolution data in the resolution range 7-3.7 A, allowing the positions of most side chains to be determined. The better quality of the 7-3.7 A resolution map is presumably a consequence of the presence of satellite crystals. The position of the second particle was improved using the correlation coefficient in the averaging process to monitor the refinement by moving the particle around in small steps.

The R-type pyocin of Pseudomonas aeruginosa C is a bacteriophage tail-like particle that contains single-stranded DNA

Pseudomonas aeruginosa R-type pyocin particles have been described as bacteriocins that resemble bacteriophage tail-like structures. Because of their unusual structure, we reexamined whether they contained nucleic acids. Our data indicated that pyocin particles isolated from P. aeruginosa C (pyocin C) contain DNA. Probes generated from this DNA by the random-primer extension method hybridized to distinct bands in restriction endonuclease-digested P. aeruginosa C genomic DNA. These probes also hybridized to genomic DNA from 6 of 18 P. aeruginosa strains that produced R-type pyocins. Asymmetric PCR, complementary oligonucleotide hybridization, and electron microscopy indicated that pyocin C particles contained closed circular single-stranded DNA, approximately 4.0 kb in length. Examination of total intracellular DNA from mitomycin C-induced cultures revealed the presence of two extrachromosomal DNA molecules, a double-stranded molecule and a single-stranded molecule, which hybridized to pyocin DNA. Sequence analysis of 7,480 nucleotides of P. aeruginosa C chromosomal DNA containing the pyocin DNA indicated the presence of pyocin open reading frames with similarities to open reading frames from filamentous phages and cryptic phage elements. We did not observe any similarities to known phage structural proteins or previously characterized pseudomonal prt genes expressing R-type pyocin structural proteins. These studies demonstrate that pyocin particles from P. aeruginosa C are defective phages that contain a novel closed circular single-stranded DNA and that this DNA was derived from the chromosome of P. aeruginosa C.

Efficacy and mechanisms of action of sodium hypochlorite on Pseudomonas aeruginosa PAO1 phage F116

The Pseudomonas aeruginosa PAO1 phage F116 was used to investigate the viricidal activity and the mechanism of action of sodium hypochlorite. The bacteriophage was inactivated with a low concentration (0.0005% available chlorine) of the biocide prepared in tap water but it was less sensitive to a sodium hypochlorite solution prepared in ultra-pure water (0.0075% available chlorine). For all the effective concentrations of sodium hypochlorite (i.e. producing at least 4 log reduction in phage titre), F116 was readily inactivated within 30 s. Electron microscopical investigations of the phage particles challenged with sodium hypochlorite showed a wide variety of deleterious effects, some of which have not been previously observed with other biocides. The wide range of structural alterations observed suggested that sodium hypochlorite has multiple target sites against F116 bacteriophage. A 30 s exposure to sodium hypochlorite (0.001% available chlorine) produced severe damage, the number and severity of which increased with a higher concentration (0.0075% available chlorine) and with a longer contact time. These observations suggested that sodium hypochlorite inactivated F116 bacteriophage by causing structural alterations to the phage head, tail and overall structure, hence possibly releasing the viral genome from damaged capsids in the surrounding media.

Resistance of Pseudomonas aeruginosa PAO1 phage F116 to sodium hypochlorite

The development of viral resistance to sodium hypochlorite was investigated using the Pseudomonas aeruginosa bacteriophage F116 as a model system. This phage was chosen because of its structural characteristics and former investigations conducted in this laboratory. F116 was shown to be sensitive to a sodium hypochlorite concentration of 0.0075 gl-1 (available chlorine) which produced a 5 log10 reduction in titre in a suspension test. Survival bacteriophages challenged with this sodium hypochlorite concentration were isolated, propagated and challenged again with the same and higher concentrations of the biocide. It was observed that progeny virions were becoming increasingly resistant to sodium hypochlorite challenges up to a concentration of 0.0175 gl-1 of available chlorine. It was also noticed that 1-2 log10 of F116 virions from resistant phage lysates remained sensitive to the biocide. An electron microscopical investigation of F116 resistant lysates showed that the phage resistance to sodium hypochlorite was not caused by F116 particles aggregation. Furthermore, no morphological difference between the sensitive and resistant F116 particles to sodium hypochlorite was identified.

[Initial stages of interaction of temperate phage 04 with Pseudomonas aeruginosa cells]

The first steps of the interaction of the temperate pilus-dependent phage 04 with susceptible and 04-lysogenic cells of Pseudomonas aeruginosa were investigated. The 04-lysogenic cells retained their ability to adsorb viral particles on the pili. However, after the translocation to the cell surface, the bacteriophage failed to infect the immune microorganism. It is assumed that was modified the surface of 04-immune cells due to lysogenic conversion, and this modification presented the terminal tail fibers of viral particles interacting from with the outer membrane of P. aeruginosa cells.

Electronmicroscopic investigation of the effects of biocides on Pseudomonas aeruginosa PAO bacteriophage F116

Electronmicroscopy was used to observe morphological changes of the Pseudomonas aeruginosa PA0 bacteriophage F116 when treated with various biocides commonly used as antibacterial and antifungal agents. Because of its large size (145 nm) and its organised structure (an isometric head and a tail), it was possible to classify structural damage into eight categories. The morphological changes induced depended on the type of biocide used and its concentration. Glutaraldehyde increased the number of phages with empty heads. Peracetic acid and phenol altered the appearance of the viral genome packaged inside the head, produced fractured heads, and damaged the tail. Peracetic acid also induced folding of the phage heads. The alcohols tested also altered the head structure. Cetylpyridinium chloride induced mainly fractured head damage. Chlorhexidine had little effect on the structure of F116.