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Recombination is the main driver of bacteriophage evolution. It may serve as a tool for extending the phage host spectrum, which is significant not only for phages' ecology but also for their utilisation as therapeutic agents of bacterial infections. The aim of this study was to detect the recombination events in the genomes of Litunavirus phages infecting Pseudomonas aeruginosa , and present their impact on phylogenetic relations within this phage group. The phylogenetic analyses involved: the whole-genome, core-genome ( Schitoviridae conserved genes), variable genome region, and the whole-genome minus variable region. Interestingly, the recombination events taking place in the putative host recognition region (tail fibre protein gene and the adjacent downstream gene) significantly influenced tree topology, suggesting a strong phylogenetic signal. Our results indicate the recombination between phages from two genera Litunavirus and Luzeptimavirus and demonstrate its influence on phage phylogeny.

Two newly discovered bacteriophages, isolated from chicken feces and infecting Salmonella enterica strains, are described in this report. These phages have been named vB_Sen-TO17 and vB_Sen-E22, and we present their molecular and functional characterization. Both studied viruses are able to infect several S. enterica strains and develop lytically, but their specific host ranges differ significantly. Electron microscopic analyses of virions have been performed, and full genome sequences were determined and characterized, along with molecular phylogenetic studies. Genomes of vB_Sen-TO17 (ds DNA of 41,658 bp) and vB_Sen-E22 (dsDNA of 108,987 bp) are devoid of homologs of any known or putative gene coding for toxins or any other proteins potentially deleterious for eukaryotic cells. Both phages adsorbed efficiently (>95% adsorbed virions) within 10 min at 42 °C (resembling chicken body temperature) on cells of most tested host strains. Kinetics of lytic development of vB_Sen-TO17 and vB_Sen-E22, determined in one-step growth experiments, indicated that development is complete within 30-40 min at 42 °C, whereas burst sizes vary from 9 to 79 progeny phages per cell for vB_Sen-TO17 and from 18 to 64 for vB_Sen-E22, depending on the host strain. Virions of both phages were relatively stable (from several percent to almost 100% survivability) under various conditions, including acidic and alkaline pH values (from 3 to 12), temperatures from -80 °C to 60 °C, 70% ethanol, chloroform, and 10% DMSO. These characteristics of vB_Sen-TO17 and vB_Sen-E22 indicate that these phages might be considered in further studies on phage therapy, particularly in attempts to eliminate S. enterica from chicken intestine.

A newly isolated bacteriophage infecting Enterococcus faecalis strains has been characterized, including determination of its molecular features. This phage, named vB_EfaS-271, has been classified as a Siphoviridae member, according to electron microscopy characterization of the virions, composed of a 50 nm-diameter head and a long, flexible, noncontractable tail (219 × 12.5 nm). Analysis of the whole dsDNA genome of this phage showed that it consists of 40,197 bp and functional modules containing genes coding for proteins that are involved in DNA replication (including DNA polymerase/primase), morphogenesis, packaging and cell lysis. Mass spectrometry analysis allowed us to identify several phage-encoded proteins. vB_EfaS-271 reveals a relatively narrow host range, as it is able to infect only a few E. faecalis strains. On the other hand, it is a virulent phage (unable to lysogenize host cells), effectively and quickly destroying cultures of sensitive host bacteria, with a latent period as short as 8 min and burst size of approximately 70 phages per cell at 37 °C. This phage was also able to destroy biofilms formed by E. faecalis . These results contribute to our understanding of the biodiversity of bacteriophages, confirming the high variability among these viruses and indicating specific genetic and functional features of vB_EfaS-271.

Molecular and functional characterization of a series of three bacteriophages, vB_SenM-1, vB_SenM-2, and vB_SenS-3, infecting various Salmonella enterica serovars and strains is presented. All these phages were able to develop lytically while not forming prophages. Moreover, they were able to survive at pH 3. The phages revealed different host ranges within serovars and strains of S. enterica, different adsorption rates on host cells, and different lytic growth kinetics at various temperatures (in the range of 25 to 42 °C). They efficiently reduced the number of cells in the bacterial biofilm and decreased the biofilm mass. Whole genome sequences of these phages have been determined and analyzed, including their phylogenetic relationships. In conclusion, we have demonstrated detailed characterization of a series of three bacteriophages, vB_SenM-1, vB_SenM-2, and vB_SenS-3, which reveal favorable features in light of their potential use in phage therapy of humans and animals, as well as for food protection purposes.

A large scale analysis presented in this article focuses on biological and physiological variety of bacteriophages. A collection of 83 bacteriophages, isolated from urban sewage and able to propagate in cells of different bacterial hosts, has been obtained (60 infecting Escherichia coli, 10 infecting Pseudomonas aeruginosa, 4 infecting Salmonella enterica, 3 infecting Staphylococcus sciuri, and 6 infecting Enterococcus faecalis). High biological diversity of the collection is indicated by its characteristics, both morphological (electron microscopic analyses) and biological (host range, plaque size and morphology, growth at various temperatures, thermal inactivation, sensitivity to low and high pH, sensitivity to osmotic stress, survivability upon treatment with organic solvents and detergents), and further supported by hierarchical cluster analysis. By the end of the research no larger collection of phages from a single environmental source investigated by these means had been found. The finding was confirmed by whole genome analysis of 7 selected bacteriophages. Moreover, particular bacteriophages revealed unusual biological features, like the ability to form plaques at low temperature (4 °C), resist high temperature (62 °C or 95 °C) or survive in the presence of an organic solvents (ethanol, acetone, DMSO, chloroform) or detergent (SDS, CTAB, sarkosyl) making them potentially interesting in the context of biotechnological applications.

We present the first attempt at quantitative analysis of morphological diversity of tailed viruses obtained from marine sediments without ultracentrifugation or enrichment on specific host strains. Sandy mud samples were collected in the Gulf of Gdańsk in the spring, autumn and winter. VLPs were analyzed by transmission electron microscopy. The distribution of three groups of tailed phages was similar in all seasons (Siphoviridae: 52% on average; Myoviridae: 42%; Podoviridae: 6%). 19% of siphoviruses had prolate heads. Interestingly, 11% of siphoviral particles had tails longer than 300 nm, and 6% longer than 600 nm., (Copyright © 2012 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.)

The characterization of a recently isolated bacteriophage, vB_Eco4M-7, which effectively infects many, though not all, Escherichia coli O157 strains, is presented. The genome of this phage comprises double-stranded DNA, 68,084 bp in length, with a GC content of 46.2%. It contains 96 putative open reading frames (ORFs). Among them, the putative functions of only 35 ORFs were predicted (36.5%), whereas 61 ORFs (63.5%) were classified as hypothetical proteins. The genome of phage vB_Eco4M-7 does not contain genes coding for integrase, recombinase, repressors or excisionase, which are the main markers of temperate viruses. Therefore, we conclude that phage vB_Eco4M-7 should be considered a lytic virus. This was confirmed by monitoring phage lytic development by a one-step growth experiment. Moreover, the phage forms relatively small uniform plaques (1 mm diameter) with no properties of lysogenization. Electron microscopic analyses indicated that vB_Eco4M-7 belongs to the Myoviridae family. Based on mass spectrometric analyses, including the fragmentation pattern of unique peptides, 33 phage vB_Eco4M-7 proteins were assigned to annotated open reading frames. Importantly, genome analysis suggested that this E. coli phage is free of toxins and other virulence factors. In addition, a similar, previously reported but uncharacterized bacteriophage, ECML-117, was also investigated, and this phage exhibited properties similar to vB_Eco4M-7. Our results indicate that both studied phages are potential candidates for phage therapy and/or food protection against Shiga toxin-producing E. coli, as the majority of these strains belong to the O157 serotype. [ABSTRACT FROM AUTHOR]

Morphological, biological, and genetic characteristics of a virulent Siphoviridae phage, named vB-EcoS-95, is reported. This phage was isolated from urban sewage. It was found to infect some Escherichia coli strains giving clear plaques. The genome of this phage is composed of 50,910 bp and contains 89 ORFs. Importantly, none of the predicted ORFs shows any similarity with known pathogenic factors that would prevent its use in medicine. Genome sequence analysis of vB-EcoS-95 revealed 74% similarity to genomic sequence of Shigella phage pSf-1. Compared to pSf-1, phage vb-EcoS-95 does not infect Shigella strains and has an efficient bacteriolytic activity against some E. coli strains. One-step growth analysis revealed that this phage has a very short latent period (4 min), and average burst size of 115 plaque forming units per cell, which points to its high infectivity of host cells and strong lytic activity. The bacteriolytic effect of vB-EcoS-95 was tested also on biofilm-producing strains. These results indicate that vB-EcoS-95 is a newly discovered E. coli phage that may be potentially used to control the formation of biofilms. [ABSTRACT FROM AUTHOR]