The Bacteriophage Pf-10-A Component of the Biopesticide "Multiphage" Used to Control Agricultural Crop Diseases Caused by Pseudomonas syringae

Phytopathogenic pseudomonads are widespread in the world and cause a wide range of plant diseases. In this work, we describe the Pseudomonas phage Pf-10, which is a part of the biopesticide "Multiphage" used for bacterial diseases of agricultural crops caused by Pseudomonas syringae. The Pf-10 chromosome is a dsDNA molecule with two direct terminal repeats (DTRs). The phage genomic DNA is 39,424 bp long with a GC-content of 56.5%. The Pf-10 phage uses a packaging mechanism based on T7-like short DTRs, and the length of each terminal repeat is 257 bp. Electron microscopic analysis has shown that phage Pf-10 has the podovirus morphotype. Phage Pf-10 is highly stable at pH values from 5 to 10 and temperatures from 4 to 60 °C and has a lytic activity against Pseudomonas strains. Phage Pf-10 is characterized by fast adsorption rate (80% of virions attach to the host cells in 10 min), but has a relatively small number of progeny (37 ± 8.5 phage particles per infected cell). According to the phylogenetic analysis, phage Pf-10 can be classified as a new phage species belonging to the genus Pifdecavirus, subfamily Studiervirinae, family Autographiviridae, order Caudovirales.

Metaviromes Reveal the Dynamics of Pseudomonas Host-Specific Phages Cultured and Uncultured by Plaque Assay

Isolating single phages using plaque assays is a laborious and time-consuming process. Whether single isolated phages are the most lyse-effective, the most abundant in viromes, or those with the highest ability to make plaques in solid media is not well known. With the increasing accessibility of high-throughput sequencing, metaviromics is often used to describe viruses in environmental samples. By extracting and sequencing metaviromes from organic waste with and without exposure to a host-of-interest, we show a host-related phage community's shift, as well as identify the most enriched phages. Moreover, we isolated plaque-forming single phages using the same virome-host matrix to observe how enrichments in liquid media correspond to the metaviromic data. In this study, we observed a significant shift (p = 0.015) of the 47 identified putative Pseudomonas phages with a minimum twofold change above zero in read abundance when adding a Pseudomonas syringae DC3000 host. Surprisingly, it appears that only two out of five plaque-forming phages from the same organic waste sample, targeting the Pseudomonas strain, were highly abundant in the metavirome, while the other three were almost absent despite host exposure. Lastly, our sequencing results highlight how long reads from Oxford Nanopore elevates the assembly quality of metaviromes, compared to short reads alone.

Improving the Inhibitory Effect of Phages against Pseudomonas aeruginosa Isolated from a Burn Patient Using a Combination of Phages and Antibiotics

Antibiotic resistance causes around 700,000 deaths a year worldwide. Without immediate action, we are fast approaching a post-antibiotic era in which common infections can result in death. Pseudomonas aeruginosa is the leading cause of nosocomial infection and is also one of the three bacterial pathogens in the WHO list of priority bacteria for developing new antibiotics against. A viable alternative to antibiotics is to use phages, which are bacterial viruses. Yet, the isolation of phages that efficiently kill their target bacteria has proven difficult. Using a combination of phages and antibiotics might increase treatment efficacy and prevent the development of resistance against phages and/or antibiotics, as evidenced by previous studies. Here, in vitro populations of a Pseudomonas aeruginosa strain isolated from a burn patient were treated with a single phage, a mixture of two phages (used simultaneously and sequentially), and the combination of phages and antibiotics (at sub-minimum inhibitory concentration (MIC) and MIC levels). In addition, we tested the stability of these phages at different temperatures, pH values, and in two burn ointments. Our results show that the two-phages-one-antibiotic combination had the highest killing efficiency against the P. aeruginosa strain. The phages tested showed low stability at high temperatures, acidic pH values, and in the two ointments. This work provides additional support for the potential of using combinations of phage-antibiotic cocktails at sub-MIC levels for the treatment of multidrug-resistant P. aeruginosa infections.

Complete genome analysis of PaGz-1 and PaZq-1, two novel phages belonging to the genus Pakpunavirus

Pseudomonas phages PaGz-1 and PaZq-1, two new phages infecting Pseudomonas aeruginosa, were isolated from fresh water in Guangdong province, China. The genomes of these two phages consist of 93,975 bp and 94,315 bp and contain 175 and 172 open reading frames (ORFs), respectively. The genome sequences of PaGz-1 and PaZq-1 share 95.8% identity with a query coverage of 94%, suggesting that these two phages belong to two different species. Based on results of nucleotide sequence alignment, gene annotation, and phylogenetic analysis, we propose PaGz-1 and PaZq-1 as representative isolates of two species in the genus Pakpunavirus within the family Myoviridae.

Pseudomonas Phage PaBG-A Jumbo Member of an Old Parasite Family

Bacteriophage PaBG is a jumbo Myoviridae phage isolated from water of Lake Baikal. This phage has limited diffusion ability and thermal stability and infects a narrow range of Pseudomonas aeruginosa strains. Therefore, it is hardly suitable for phage therapy applications. However, the analysis of the genome of PaBG presents a number of insights into the evolutionary history of this phage and jumbo phages in general. We suggest that PaBG represents an ancient group distantly related to all known classified families of phages.

Pseudomonas PB1-Like Phages: Whole Genomes from Metagenomes Offer Insight into an Abundant Group of Bacteriophages

Despite the abundance, ubiquity and impact of environmental viruses, their inherent genomic plasticity and extreme diversity pose significant challenges for the examination of bacteriophages on Earth. Viral metagenomic studies have offered insight into broader aspects of phage ecology and repeatedly uncover genes to which we are currently unable to assign function. A combined effort of phage isolation and metagenomic survey of Chicago’s nearshore waters of Lake Michigan revealed the presence of Pbunaviruses, relatives of the Pseudomonas phage PB1. This prompted our expansive investigation of PB1-like phages. Genomic signatures of PB1-like phages and Pbunaviruses were identified, permitting the unambiguous distinction between the presence/absence of these phages in soils, freshwater and wastewater samples, as well as publicly available viral metagenomic datasets. This bioinformatic analysis led to the de novo assembly of nine novel PB1-like phage genomes from a metagenomic survey of samples collected from Lake Michigan. While this study finds that Pbunaviruses are abundant in various environments of Northern Illinois, genomic variation also exists to a considerable extent within individual communities.

Genomic characterization and phylogenetic analysis of the novel Pseudomonas phage PPSC2

We isolated a Pseudomonas phage infecting Pseudomonas fluorescens SA1 separated from a soil sample collected in Sichuan Province, China. This phage, which we named PPSC2, has a genome that is composed of a 97,330-bp-long linear double-stranded DNA with 47.51% G+C content and 168 putative protein-coding genes. We identified 20 tRNA genes in the genome of PPSC2, and the tRNA GC content ranged from 44.2% to 58.4%. Phylogenetic and BLASTn analysis revealed that the Pseudomonas phage PPSC2 should be considered a new member of the family Myoviridae.

Differential Effect of Newly Isolated Phages Belonging to PB1-Like, phiKZ-Like and LUZ24-Like Viruses against Multi-Drug Resistant Pseudomonas aeruginosa under Varying Growth Conditions

In this study, we characterize three phages (SL1 SL2, and SL4), isolated from hospital sewage with lytic activity against clinical isolates of multi-drug resistant Pseudomonas aeruginosa (MDR-PA). The host spectrum ranged from 41% to 54%, with all three phages together covering 79% of all tested clinical isolates. Genome analysis revealed that SL1 (65,849 bp, 91 open reading frames ORFs) belongs to PB1-like viruses, SL2 (279,696 bp, 354 ORFs) to phiKZ-like viruses and SL4 (44,194 bp, 65 ORFs) to LUZ24-like viruses. Planktonic cells of four of five selected MDR-PA strains were suppressed by at least one phage with multiplicities of infection (MOIs) ranging from 1 to 10⁻⁶ for 16 h without apparent regrowth of bacterial populations. While SL2 was most potent in suppressing planktonic cultures the strongest anti-biofilm activity was observed with SL4. Phages were able to rescue bacteria-infected wax moth larvae (Galleria melonella) for 24 h, whereby highest survival rates (90%) were observed with SL1. Except for the biofilm experiments, the effect of a cocktail with all three phages was comparable to the action of the best phage alone; hence, there are no synergistic but also no antagonistic effects among phages. The use of a cocktail with these phages is therefore expedient for increasing host range and minimizing the development of phage resistance.

[New Virulent Bacteriophages Active against Multiresistant Pseudomonas aeruginosa Strains]

The sensitivity of 512 newly isolated Pseudomonas aeruginosa clinical strains to six classes of anti-microbial preparations has been studied. Antibiotic-resistant strains were selected and genotyped. Three new virulent bacteriophages of the families Myoviridae and Podoviridae were isolated against these strains. The parameters of the intracellular phage development cycle were established, and the influence of inactivating factors (temperature, pH, and UV exposure) on phage viability was studied. The molecular weight of the phage genome was determined. Phage DNA restriction analysis and polyacrylamide gel electrophoresis in the presence of envelope protein SDS were carried out. The plating efficacy of phages on 28 genetically distant antibiotic-resistant P. aeruginosa strains was studied. It was established that 26 of them were lysed by phages with a high efficacy. The range of antibacterial action of the studied phages and their mixtures on 427 multi-drug-resistant clinical isolates was assessed. It is shown that including these phages in one multicomponent preparation enhanced their lytic activity.

The search for therapeutic bacteriophages uncovers one new subfamily and two new genera of Pseudomonas-infecting Myoviridae

In a previous study, six virulent bacteriophages PAK_P1, PAK_P2, PAK_P3, PAK_P4, PAK_P5 and CHA_P1 were evaluated for their in vivo efficacy in treating Pseudomonas aeruginosa infections using a mouse model of lung infection. Here, we show that their genomes are closely related to five other Pseudomonas phages and allow a subdivision into two clades, PAK_P1-like and KPP10-like viruses, based on differences in genome size, %GC and genomic contents, as well as number of tRNAs. These two clades are well delineated, with a mean of 86% and 92% of proteins considered homologous within individual clades, and 25% proteins considered homologous between the two clades. By ESI-MS/MS analysis we determined that their virions are composed of at least 25 different proteins and electron microscopy revealed a morphology identical to the hallmark Salmonella phage Felix O1. A search for additional bacteriophage homologs, using profiles of protein families defined from the analysis of the 11 genomes, identified 10 additional candidates infecting hosts from different species. By carrying out a phylogenetic analysis using these 21 genomes we were able to define a new subfamily of viruses, the Felixounavirinae within the Myoviridae family. The new Felixounavirinae subfamily includes three genera: Felixounalikevirus, PAK_P1likevirus and KPP10likevirus. Sequencing genomes of bacteriophages with therapeutic potential increases the quantity of genomic data on closely related bacteriophages, leading to establishment of new taxonomic clades and the development of strategies for analyzing viral genomes as presented in this article.

[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.

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.

Genome sequence comparison and superinfection between two related Pseudomonas aeruginosa phages, D3112 and MP22

A temperate transposable bacteriophage (MP22) was isolated from a Korean clinical isolate of Pseudomonas aeruginosa. It has a coliphage lambda-like morphology and a double-stranded DNA genome. The complete nucleotide sequence and annotation of the MP22 genome and its characteristics are presented. The MP22 genome is 36 409 bp long with a G+C content of 64.2 mol%. The genome contains 51 proposed ORFs, of which 48 (94 %) display synteny and significant nucleotide and protein sequence similarity to the corresponding ORFs of the closely related phage, D3112. Three of the predicted ORFs are unique proteins, whose functions are yet to be revealed. The phage c repressors exhibit striking dissimilarities and, when present as a single gene, did not show cross-immunity. In contrast, although an MP22 lysogen could be productively infected with D3112, MP22 could not grow on a D3112 lysogen, indicating a role of other D3112 genes in superinfection exclusion.

"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.

Comparative genomic analysis of 18 Pseudomonas aeruginosa bacteriophages

A genomic analysis of 18 P. aeruginosa phages, including nine newly sequenced DNA genomes, indicates a tremendous reservoir of proteome diversity, with 55% of open reading frames (ORFs) being novel. Comparative sequence analysis and ORF map organization revealed that most of the phages analyzed displayed little relationship to each other.

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.

[Phenogenetic characterization of a group of giant Phi KZ-like bacteriophages of Pseudomonas aeruginosa]

A comparative study was made of a group of Pseudomonas aeruginosa virulent giant DNA bacteriophages similar to phage phi KZ in several genetic and phenotypic properties (particle size, particle morphology, genome size, appearance of negative colonies, high productivity, broad spectrum of lytic activity, ability to overcome the suppressing effect of plasmids, absence of several DNA restriction sites, capability of general transduction, pseudolysogeny). We have recently sequenced the phage phi KZ genome (288,334 bp) [J. Mol. Biol., 2002, vol. 317, pp. 1-19]. By DNA homology, the phages were assigned to three species (represented by phage phi KZ, Lin68, and EL, respectively) and two new genera (phi KZ and EL). Restriction enzyme analysis revealed the mosaic genome structure in four phages of the phi KZ species (phi KZ, Lin21, NN, and PTB80) and two phages of the EL species (EL and RU). Comparisons with respect to phage particle size, number of structural proteins, and the N-terminal sequences of the major capsid protein confirmed the phylogenetic relatedness of the phages belonging to the phi KZ genus. The origin and evolution of the phi KZ-like phages are discussed. Analysis of protein sequences encoded by the phage phi KZ genome made it possible to assume wide migration of the phi KZ-like phages (wandering phages) among various prokaryotes and possibly eukaryotes. Since the phage phi KZ genome codes for potentially toxic proteins, caution must be exercised in the employment of large bacteriophages in phage therapy.

[Isolation and comparative study of a group of temperate bacteriophages of rhizospheric pseudomonads Pseudomonas putida]

We have isolated several new temperate bacteriophages for rhizosphere pseudomonads Pseudomonas putida. Examination of these phages, along with two previously isolated temperate phages PP56 and PP71 of P. putida PpG1 (biovar A), allowed us to classify them into four species on the basis of DNA cross-homology; relative genomic size; and, to a certain extent, the morphology of phage particles. Two of these species are represented by nonidentical variants. No transposable phages were found among these two new species. Three phage species cause various-types of lysogenic conversion manifested in growth suppression of other phage species. This seems to account for the fact that the temperate phage of rhizosphere pseudomonads are seldom encountered. The new phages described can be used for selection of phage-resistant bacterial forms exhibiting antifungal activity that are commercially produced and used for treatment of seeds of cultivated plants.

Isolation of bacteriophages specific to a fish pathogen, Pseudomonas plecoglossicida, as a candidate for disease control

Two types of bacteriophage specific to Pseudomonas plecoglossicida, the causative agent of bacterial hemorrhagic ascites disease in cultured ayu fish (Plecoglossus altivelis), were isolated from diseased ayu and the rearing pond water. One type of phage, which formed small plaques, was tentatively classified as a member of the family Myoviridae, and the other type, which formed large plaques, was classified as a member of the family Podoviridae. All 27 strains of P. plecoglossicida examined, which were isolated from diseased ayu from geographically different areas in 1991 to 1999, exhibited quite similar sensitivities to either type of phage. One strain of P. plecoglossicida was highly virulent for ayu, and the 50% lethal dose (LD(50)) when intramuscular injection was used was 10(1.2) CFU fish(-1); in contrast, phage-resistant variants of this organism were less virulent (LD(50), >10(4) CFU fish(-1)). Oral administration of phage-impregnated feed to ayu resulted in protection against experimental infection with P. plecoglossicida. After oral administration of P. plecoglossicida cells of this bacterium were always detected in the kidneys of control fish that did not receive the phage treatment, while the cells quickly disappeared from the phage-treated fish. Bacterial growth in freshwater was lower in the presence of phage, and the number of phage PFU increased rapidly. These results suggest that it may be possible to use phage to control the disease caused by P. plecoglossicida.

Pseudomonas aeruginosa phage lysate as an immunobiological agent. 1. Selection of Pseudomonas aeruginosa clinical strains for phage lysate preparation

A total of 2087 Pseudomonas aeruginosa isolates collected during the period 1994-1997 were used as starting material. Out of 1704 in-patient isolates, 299 strains were selected for the preparation of phage lysates but only five strains provided stable lysates, i.e., maintained the ability to be repeatedly and completely lysed by the appropriate phage in the course of several years. A set of 193 out-patients (189) and water sources (4) isolates failed to yield strains suitable for phage lysate preparation; 190 strains isolated abroad from patients with cystic fibrosis or respiratory infections included three isolates which, despite having a high degree of mucus production, were suitable for lysate preparation. The antigenic pattern of the phage lysates was ascertained by SDS-polyacrylamide gel electrophoresis.

[The isolation and characteristics of cloned strains of Pseudomonas pseudomallei phages]

On the basis of museum strains of the melioidosis agent Pseudomonas pseudomallei, 14 pure lines of bacteriophages were isolated belonging to morphological groups IV and V according to the classification by A. S. Tikhonenko. These phages show a broad bacteriolytic range as far as museum P. pseudomallei cultures are concerned. It was determined that some phages isolated from the same melioidosis culture and belonging to the same morphological type display different bacteriolytic activity. It is demonstrated that some strains of melioidosis agent are characterized by polylysogeny.

Cytotoxin-converting phages, phi CTX and PS21, are R pyocin-related phages

phi CTX is a temperate phage of Pseudomonas aeruginosa harbouring the ctx gene that encodes cytotoxin (CTX). We identified phi CTX as an R pyocin-related phage, by serological and molecular analysis, based on the findings that the infectivity of the phage was inhibited with the antisera directed R pyocins and R pyocin-related phages and that the phi CTX genome showed DNA homology to the genome of PS17 (a representative of the R pyocin-related phages) as well as to the pyocin R2 genes. Another new CTX-converting, R pyocin-related phage named PS21 was isolated from a CTX-producing strain of P. aeruginosa, suggesting the distribution of the ctx gene by certain members of R pyocin-related phage family.

DNA homology in species of bacteriophages active on Pseudomonas aeruginosa

Using electron microscopy and DNA-DNA-hybridization, 113 virulent and temperate bacteriophages specific for P. aeruginosa have been assigned to 23 species. In most cases, especially in virulent phages, both particle morphology and DNA homology types were in good correlation and their use was sufficient for clear-cut definition of phage species. No virulent phages of different species had any DNA homology. DNA homology was detected between temperate phages of several species. Temperate phages formed two large groups of two and seven species, respectively. The first group included all transposable bacteriophages. The extent of interspecies DNA homology of phages belonging to each group was not more than 10-15% (except for 25% for phages D 3 and KF 1). No DNA homology was between phages of different groups. The possible origin and function of homologous sequences (genetic modules, linkers, occasional insertional sequences) are discussed. One of the phages (phi C 15) may be considered as the result of recombination between phages belonging to two different species, 295 and SM.