Distribution and characterization of prophages in Lactobacillus plantarum derived from kimchi.

Prophage distribution and phage characteristics based on the genome of Lactobacillus plantarum derived from kimchi were investigated. Prophage genomes retrieved from a database were analyzed in silico with prophage inducibility. Twenty-one kimchi-derived L. plantarum had at least one intact prophage, including a putative cryptic state on the chromosome. They were all confirmed to belong to the Siphoviridae family. Intact prophages can be classified into three different groups: PM411-like, Sha1-like, and unclassified phage groups. Some prophage regions were encoded with superinfection exclusion proteins and orphan methylases, suggesting that the phages co-evolved with their hosts. Interestingly, prophage inducibility showed that only DNA damage could induce prophages and that pH stresses by organic acids could not. Therefore, the prophage of L. plantarum did not affect the host unless DNA was damaged, and it would hardly affect the viability of the host through phage induction during kimchi fermentation. Our results might provide insights into the distribution and non-inducibility of prophages, existence of phage-immunity genes, and role of plant-derived L. plantarum prophages in host survival during late acidic kimchi fermentation.

Exploring Codon Adjustment Strategies towards Escherichia coli-Based Production of Viral Proteins Encoded by HTH1, a Novel Prophage of the Marine Bacterium Hypnocyclicus thermotrophus.

Marine viral sequence space is immense and presents a promising resource for the discovery of new enzymes interesting for research and biotechnology. However, bottlenecks in the functional annotation of viral genes and soluble heterologous production of proteins hinder access to downstream characterization, subsequently impeding the discovery process. While commonly utilized for the heterologous expression of prokaryotic genes, codon adjustment approaches have not been fully explored for viral genes. Herein, the sequence-based identification of a putative prophage is reported from within the genome of Hypnocyclicus thermotrophus, a Gram-negative, moderately thermophilic bacterium isolated from the Seven Sisters hydrothermal vent field. A prophage-associated gene cluster, consisting of 46 protein coding genes, was identified and given the proposed name Hypnocyclicus thermotrophus phage H1 (HTH1). HTH1 was taxonomically assigned to the viral family Siphoviridae, by lowest common ancestor analysis of its genome and phylogeny analyses based on proteins predicted as holin and DNA polymerase. The gene neighbourhood around the HTH1 lytic cassette was found most similar to viruses infecting Gram-positive bacteria. In the HTH1 lytic cassette, an N-acetylmuramoyl-L-alanine amidase (Amidase_2) with a peptidoglycan binding motif (LysM) was identified. A total of nine genes coding for enzymes putatively related to lysis, nucleic acid modification and of unknown function were subjected to heterologous expression in Escherichia coli. Codon optimization and codon harmonization approaches were applied in parallel to compare their effects on produced proteins. Comparison of protein yields and thermostability demonstrated that codon optimization yielded higher levels of soluble protein, but codon harmonization led to proteins with higher thermostability, implying a higher folding quality. Altogether, our study suggests that both codon optimization and codon harmonization are valuable approaches for successful heterologous expression of viral genes in E. coli, but codon harmonization may be preferable in obtaining recombinant viral proteins of higher folding quality.

Genetic diversity and population structure of 'Candidatus Liberibacter asiaticus' associated with citrus Huanglongbing in India based on the prophage types.

Huanglongbing (HLB), also known as 'citrus greening', is an extremely destructive disease of citrus worldwide. HLB is associated with three species of the fastidious proteobacterium, Candidatus Liberibacter asiaticus (CaLas), Ca. L. africanus and Ca. L. americanus with CaLas being the most widely distributed around the world and the only species detected and described so far in India, one of the major global citrus fruit producers. Prophages are highly dynamic components in the bacterial genome and play an important role in intraspecies variations. Three types of prophages, Type 1, Type 2 and Type 3 have been identified and described in CaLas so far. In the present study, 441 CaLas isolates sampled across 18 Indian states were used for prophage typing. Based on detection of three prophage types by PCR, all the eight probable combinations of CaLas prophages were identified, including single Type 1 (26.5%), single Type 2 (18.8%), single Type 3 (1.4%), Type 1 + Type 2 (20.4%), Type 1 + Type 3 (12.5%), Type 2 + Type 3 (4.8%), Type 1 + Type 2 + Type 3 (11.3%) and None type (4.3%). Prophage types were confirmed by PCR amplicon sequencing and subsequent phylogenetic analysis. By discovery of all 3 prophages and based on genetic identity and genetic distance, CaLas populations from eighteen citrus growing states were separated into two major Prophage Typing Groups (PTGs): PTG1 and PTG2. The PTG1 comprised of CaLas from North-West India and PTG2 from rest of the country (North-East, Central and South India), and both major groups were further divided into two (PTG1-A, PTG1-B) and three (PTG2-A, PTG2-B and PTG2-C) subgroups respectively. The findings of CaLas population patterns provide evidence for independent origins of HLB-associated CaLas. CRISPR (clustered regularly interspaced short palindromic repeats) array was also detected in CaLas isolates. This is the first report evaluating the genetic variation of a large population of CaLas bacterium in India using the PCR markers from the prophage regions which would certainly assist the ongoing HLB management efforts in India.

Complete genome sequence of the newly discovered temperate Clostridioides difficile bacteriophage phiCDKH01 of the family Siphoviridae.

A temperate siphovirus, phiCDKH01, was obtained from a clinical isolate of Clostridioides difficile. The phage genome is a 45,089-bp linear double-stranded DNA molecule with an average G+C content of 28.7%. It shows low similarity to known phage genomes, except for phiCD24-1. Genomic and phylogenetic analysis revealed that phiCDKH01 is a newly discovered phage. Sixty-six putative ORFs were predicted in the genome, 37 of which code for proteins with predicted functions. The phiCDKH01 prophage was localized in the host genome. The results of this study increase our knowledge about the genetic diversity of tailed phages.

Examination of Staphylococcus aureus Prophages Circulating in Egypt.

Staphylococcus aureus infections are of growing concern given the increased incidence of antibiotic resistant strains. Egypt, like several other countries, has seen alarming increases in methicillin-resistant S. aureus (MRSA) infections. This species can rapidly acquire genes associated with resistance, as well as virulence factors, through mobile genetic elements, including phages. Recently, we sequenced 56 S. aureus genomes from Alexandria Main University Hospital in Alexandria, Egypt, complementing 17 S. aureus genomes publicly available from other sites in Egypt. In the current study, we found that the majority (73.6%) of these strains contain intact prophages, including Biseptimaviruses, Phietaviruses, and Triaviruses. Further investigation of these prophages revealed evidence of horizontal exchange of the integrase for two of the prophages. These Egyptian S. aureus prophages are predicted to encode numerous virulence factors, including genes associated with immune evasion and toxins, including the Panton-Valentine leukocidin (PVL)-associated genes lukF-PV/lukS-PV. Thus, prophages are likely to be a major contributor to the virulence of S. aureus strains in circulation in Egypt.

Comprehensive in silico survey of the Mycolicibacterium mobilome reveals an as yet underexplored diversity.

The mobilome plays a crucial role in bacterial adaptation and is therefore a starting point to understand and establish the gene flow occurring in the process of bacterial evolution. This is even more so if we consider that the mobilome of environmental bacteria can be the reservoir of genes that may later appear in the clinic. Recently, new genera have been proposed in the family Mycobacteriaceae, including the genus Mycolicibacterium, which encompasses dozens of species of agricultural, biotechnological, clinical and ecological importance, being ubiquitous in several environments. The current scenario in the Mycobacteriaceae mobilome has some bias because most of the characterized mycobacteriophages were isolated using a single host strain, and the few plasmids reported mainly relate to the genus Mycobacterium. To fill in the gaps in these issues, we performed a systematic in silico study of these mobile elements based on 242 available genomes of the genus Mycolicibacterium. The analyses identified 156 putative plasmids (19 conjugative, 45 mobilizable and 92 non-mobilizable) and 566 prophages in 86 and 229 genomes, respectively. Moreover, a contig was characterized by resembling an actinomycete integrative and conjugative element (AICE). Within this diversity of mobile genetic elements, there is a pool of genes associated with several canonical functions, in addition to adaptive traits, such as virulence and resistance to antibiotics and metals (mercury and arsenic). The type-VII secretion system was a common feature in the predicted plasmids, being associated with genes encoding virulent proteins (EsxA, EsxB, PE and PPE). In addition to the characterization of plasmids and prophages of the family Mycobacteriaceae, this study showed an abundance of these genetic elements in a dozen species of the genus Mycolicibacterium.

Characterization of Clinical and Carrier Streptococcus agalactiae and Prophage Contribution to the Strain Variability.

Streptococcus agalactiae (group B Streptococcus, GBS) represents a leading cause of invasive bacterial infections in newborns and is also responsible for diseases in older and immunocompromised adults. Prophages represent an important factor contributing to the genome plasticity and evolution of new strains. In the present study, prophage content was analyzed in human GBS isolates. Thirty-seven prophages were identified in genomes of 20 representative sequenced strains. On the basis of the sequence comparison, we divided the prophages into eight groups named A-H. This division also corresponded to the clustering of phage integrase, even though several different integration sites were observed in some relative prophages. Next, PCR method was used for detection of the prophages in 123 GBS strains from adult hospitalized patients and from pregnancy screening. At least one prophage was present in 105 isolates (85%). The highest prevalence was observed for prophage group A (71%) and satellite prophage group B (62%). Other groups were detected infrequently (1-6%). Prophage distribution did not differ between clinical and screening strains, but it was unevenly distributed in MLST (multi locus sequence typing) sequence types. High content of full-length and satellite prophages detected in present study implies that prophages could be beneficial for the host bacterium and could contribute to evolution of more adapted strains.

Characterization of φEf-vB1 prophage infecting oral Enterococcus faecalis and enhancing bacterial biofilm formation.

Introduction. Enterococcus faecalis is a facultative, anaerobic, opportunistic pathogen associated with medical and dental diseases. Bacterial phenotypic traits and pathogenesis are often influenced by lysogeny.Aim. The aim of this study was to characterize both the morphology and complete genome sequences of induced prophages purified from E. faecalis clinical isolates.Methodology. E. faecalis isolates were recovered from the roots of teeth of patients attending an endodontic clinic. The morphological features of isolated phage were characterized using transmission electron microscopy (TEM). DNA sequencing was performed using the Illumina MiSeq platform.Results. TEM indicated that the isolated φEf-vB1 prophage belongs to the family Siphoviridae. The φEf-vB1 prophage was stable over a wide range of temperatures and pH. Sequencing of φEf-vB1 DNA revealed that the phage genome is 37 561 bp in length with a G+C content of 37.6mol% and contained 53 ORFs. Comparison with previously predicted prophage genomes using blast revealed that φEf-vB1 has a high sequence similarity to previously characterized phage genomes. The lysogenic E. faecalis strain exhibited a higher biofilm formation capacity relative to the non-lysogenic strain.Conclusion. The current findings highlight the role of lysogeny in modification of E. faecalis properties and reveal the potential importance of prophages in E. faecalis biology and pathogenesis.

Genomic analysis of 40 prophages located in the genomes of 16 carbapenemase-producing clinical strains of Klebsiella pneumoniae.

Klebsiella pneumoniae is the clinically most important species within the genus Klebsiella and, as a result of the continuous emergence of multi-drug resistant (MDR) strains, the cause of severe nosocomial infections. The decline in the effectiveness of antibiotic treatments for infections caused by MDR bacteria has generated particular interest in the study of bacteriophages. In this study, we characterized a total of 40 temperate bacteriophages (prophages) with a genome range of 11.454-84.199 kb, predicted from 16 carbapenemase-producing clinical strains of K. pneumoniae belonging to different sequence types, previously identified by multilocus sequence typing. These prophages were grouped into the three families in the order Caudovirales (27 prophages belonging to the family Myoviridae, 10 prophages belonging to the family Siphoviridae and 3 prophages belonging to the family Podoviridae). Genomic comparison of the 40 prophage genomes led to the identification of four prophages isolated from different strains and of genome sizes of around 33.3, 36.1, 39.6 and 42.6 kb. These prophages showed sequence similarities (query cover >90 %, identity >99.9 %) with international Microbe Versus Phage (MVP) (http://mvp.medgenius.info/home) clusters 4762, 4901, 3499 and 4280, respectively. Phylogenetic analysis revealed the evolutionary proximity among the members of the four groups of the most frequently identified prophages in the bacterial genomes studied (33.3, 36.1, 39.6 and 42.6 kb), with bootstrap values of 100 %. This allowed the prophages to be classified into three clusters: A, B and C. Interestingly, these temperate bacteriophages did not infect the highest number of strains as indicated by a host-range assay, these results could be explained by the development of superinfection exclusion mechanisms. In addition, bioinformatic analysis of the 40 identified prophages revealed the presence of 2363 proteins. In total, 59.7 % of the proteins identified had a predicted function, mainly involving viral structure, transcription, replication and regulation (lysogenic/lysis). Interestingly, some proteins had putative functions associated with bacterial virulence (toxin expression and efflux pump regulators), phage defence profiles such as toxin-antitoxin modules, an anti-CRISPR/Cas9 protein, TerB protein (from terZABCDE operon) and methyltransferase proteins.

Identification, characterization, and phylogenetic analysis of eight new inducible prophages in Lactobacillus.

Lysogenic bacterial strains abound in the Lactobacillus genus and contain dormant prophages inserted within their genomes. To evaluate the prophage-induction potential of the Lactobacillus strains of six species, 142 randomly selected strains from these species were induced with Mitomycin C. Eight newly-induced phages were identified and found to be diverse in morphology. Among the six species assessed, Lactobacillus plantarum and Lactobacillus rhamnosus strains were generally insensitive to induction. The genomic characterizations of eight phages were performed via whole genome sequencing and protein prediction. Meanwhile, genome comparison of the induced phages and predicted prophages demonstrated that the prediction software PHASTER can accurately locate major prophage regions in Lactobacillus. A phylogenetic tree of the Lactobacillus phage population was constructed to obtain further insights into the clustering of individuals, two major groups were found, one of which consisted mostly of L. plantarum virulent phages, the other was represented by Lactobacillus casei/paracasei temperate phages. Finally, it was confirmed via genomic collinear analysis, which seven of the eight Lactobacillus temperate phages were newly discovered, and two Lactobacillus brevis temperate phages belonged to a novel lineage.

Genome analysis of the temperate bacteriophage PMBT6 residing in the genome of Bifidobacterium thermophilum MBT94004.

The Siphoviridae phage PMBT6 was identified by transmission electron microscopy in the supernatant of Bifidobacterium thermophilum MBT94004 bioreactor fermentation culture, where it occurred at a moderately high titer. Genome analysis of the bacterial DNA confirmed the presence of this prophage within the genome of the lysogenic host. Under laboratory conditions, the prophage could not be induced by mitomycin C, ultraviolet C irradiation or hydrogen peroxide, suggesting that the prophage was released by spontaneous induction under (yet unknown) bioreactor conditions. Genome sequencing of the virion resulted in a linear, double-stranded DNA molecule of 36,561 bp with a mol% G + C content of 61.7 and 61 predicted open reading frames with low similarity to other Bifidobacterium spp. genomes, confirming that PMBT6 represents a novel temperate phage for this genus.

R18C is a new viable P2-like bacteriophage of rabbit origin infecting Citrobacter rodentium and Shigella sonnei strains.

Here, we report a novel virulent P2-like bacteriophage, R18C, isolated from rabbit faeces, which, in addition to Escherichia coli K-12 strains, was able to be propagated on Citrobacter rodentium strain ICC169 and a range of Shigella sonnei strains with high efficiency of plating (EOP). It represents the first lytic bacteriophage originating from rabbit and the first infectious P2-like phage of animal origin. In the three characteristic moron-containing regions of P2-like phages, R18C contains genes with unknown function that have so far only been found in cryptic P2-like prophages.

Large Phenotypic and Genetic Diversity of Prophages Induced from the Fish Pathogen Vibrio anguillarum.

Vibrio anguillarum is a marine pathogenic bacterium that causes vibriosis in fish and shellfish. Although prophage-like sequences have been predicted in V. anguillarum strains, many are not characterized, and it is not known if they retain the functional capacity to form infectious particles that can infect and lysogenize other bacterial hosts. In this study, the genome sequences of 28 V. anguillarum strains revealed 55 different prophage-related elements. Chemical and spontaneous induction allowed a collection of 42 phage isolates, which were classified in seven different groups according to a multiplex PCR assay. One shared prophage sequence, p41 (group III), was present in 17 V. anguillarum strains, suggesting that this specific element is very dynamically exchanged among V. anguillarum populations. Interestingly, the host range of genetically identical phages was highly dependent on the strains used for proliferation, indicating that phenotypic properties of phages were partly regulated by the host. Finally, experimental evidence displayed that the induced phage ɸVa_90-11-287_p41 was able to lysogenize V. anguillarum strain Ba35, and subsequently spontaneously become released from the lysogenized cells, demonstrating an efficient transfer of the phage among V. anguillarum strains. Altogether, the results showed large genetic and functional diversity and broad distribution of prophages in V. anguillarum, and demonstrated the potential of prophages as drivers of evolution in V. anguillarum strains.

Diversity patterns of bacteriophages infecting Aggregatibacter and Haemophilus species across clades and niches.

Aggregatibacter and Haemophilus species are relevant human commensals and opportunistic pathogens. Consequently, their bacteriophages may have significant impact on human microbial ecology and pathologies. Our aim was to reveal the prevalence and diversity of bacteriophages infecting Aggregatibacter and Haemophilus species that colonize the human body. Genome mining with comparative genomics, screening of clinical isolates, and profiling of metagenomes allowed characterization of 346 phages grouped in 52 clusters and 18 superclusters. Less than 10% of the identified phage clusters were represented by previously characterized phages. Prophage diversity patterns varied significantly for different phage types, host clades, and environmental niches. A more diverse phage community lysogenizes Haemophilus influenzae and Haemophilus parainfluenzae strains than Aggregatibacter actinomycetemcomitans and "Haemophilus ducreyi". Co-infections occurred more often in "H. ducreyi". Phages from Aggregatibacter actinomycetemcomitans preferably lysogenized strains of specific serotype. Prophage patterns shared by subspecies clades of different bacterial species suggest similar ecoevolutionary drivers. Changes in frequencies of DNA uptake signal sequences and guanine-cytosine content reflect phage-host long-term coevolution. Aggregatibacter and Haemophilus phages were prevalent at multiple oral sites. Together, these findings should help exploring the ecoevolutionary forces shaping virus-host interactions in the human microbiome. Putative lytic phages, especially phiKZ-like, may provide new therapeutic options.

A novel uncultured marine cyanophage lineage with lysogenic potential linked to a putative marine Synechococcus 'relic' prophage.

Marine cyanobacteria are important contributors to primary production in the ocean and their viruses (cyanophages) affect the ocean microbial communities. Despite reports of lysogeny in marine cyanobacteria, a genome sequence of such temperate cyanophages remains unknown although genomic analysis indicate potential for lysogeny in certain marine cyanophages. Using assemblies from Red Sea and Tara Oceans metagenomes, we recovered genomes of a novel uncultured marine cyanophage lineage, which contain, in addition to common cyanophage genes, a phycobilisome degradation protein NblA, an integrase and a split DNA polymerase. The DNA polymerase forms a monophyletic clade with a DNA polymerase from a genomic island in Synechococcus WH8016. The island contains a relic prophage that does not resemble any previously reported cyanophage but shares several genes with the newly identified cyanophages reported here. Metagenomic recruitment indicates that the novel cyanophages are widespread, albeit at low abundance. Here, we describe a novel potentially lysogenic cyanophage family, their abundance and distribution in the marine environment.

Classifying the Unclassified: A Phage Classification Method.

This work reports the method ClassiPhage to classify phage genomes using sequence derived taxonomic features. ClassiPhage uses a set of phage specific Hidden Markov Models (HMMs) generated from clusters of related proteins. The method was validated on all publicly available genomes of phages that are known to infect Vibrionaceae. The phages belong to the well-described phage families of Myoviridae, Podoviridae, Siphoviridae, and Inoviridae. The achieved classification is consistent with the assignments of the International Committee on Taxonomy of Viruses (ICTV), all tested phages were assigned to the corresponding group of the ICTV-database. In addition, 44 out of 58 genomes of Vibrio phages not yet classified could be assigned to a phage family. The remaining 14 genomes may represent phages of new families or subfamilies. Comparative genomics indicates that the ability of the approach to identify and classify phages is correlated to the conserved genomic organization. ClassiPhage classifies phages exclusively based on genome sequence data and can be applied on distinct phage genomes as well as on prophage regions within host genomes. Possible applications include (a) classifying phages from assembled metagenomes; and (b) the identification and classification of integrated prophages and the splitting of phage families into subfamilies.

Prophage LambdaSo uses replication interference to suppress reproduction of coexisting temperate phage MuSo2 in Shewanella oneidensis MR-1.

Many bacterial genomes carry multiple prophages that compete with each other, potentially affecting the physiology, fitness, and pathogenicity of their hosts. However, molecular mechanisms of such prophage-prophage conflicts remain poorly understood. The genome of Shewanella oneidensis MR-1, a Gammaproteobacterium residing in aquatic environments and notable for its ability to reduce metal ions, harbours four prophages, two of which (LambdaSo and MuSo2) form infectious virions during biofilm formation. Here, we constructed indicator strains of LambdaSo and MuSo2 by deleting the corresponding prophages from the MR-1 chromosome and investigated their reproduction. Interestingly, the fitness of MuSo2 increased in the absence of LambdaSo, suggesting that prophage LambdaSo repressed MuSo2 reproduction. Partial deletion of LambdaSo from the MR-1 chromosome revealed that gene cluster R of LambdaSo, which was responsible for the switch to the lytic cycle and LambdaSo genome replication initiation, was necessary and sufficient to repress MuSo2. Furthermore, activation of cluster R genes facilitated replication of cluster R-encoding DNA and inhibited host and MuSo2 DNA replication. These findings suggest that LambdaSo represses MuSo2 propagation by inhibiting DNA replication during simultaneous induction. We predict that such a mechanism of inter-prophage interference is more widespread in bacteria than currently appreciated.

Phylogenetic relationship of prophages is affected by CRISPR selection in Group A Streptococcus.

BACKGROUND: Group A Streptococcus (GAS) is a major human pathogen, which is associated with a wide spectrum of invasive diseases, such as pharyngitis, scarlet fever, rheumatic fever, and streptococcal toxic shock syndrome (STSS). It is hypothesized that differences in GAS pathogenicity are related to the acquisition of diverse bacteriophages (phages). Nevertheless, the GAS genome also harbors clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated (cas) genes, which play an important role in eliminating foreign DNA, including those of phages. However, the structure of prophages in GAS strains is mosaic, and the phylogenetic relationship between prophages and CRISPR is not clear. In this study, we analyzed CRISPR and prophage structure using 118 complete genome sequences of GAS strains to elucidate the relationship between two genomic elements. Additionally, phylogenetic and M-type analyses were performed. RESULTS: Of the 118 GAS strains, 80 harbored type I-C and/or II-A CRISPR/cas loci. A total of 553 spacer sequences were identified from CRISPR/cas loci and sorted into 229 patterns. We identified and classified 373 prophages into 14 groups. Some prophage groups shared a common integration site, and were related to M-type. We further investigated the correlation between spacer sequences and prophages. Of the 229 spacer sequence patterns, 203 were similar to that of other GAS prophages. No spacer showed similarity with that of a specific prophage group with mutL integration site. Moreover, the average number of prophages in strains with type II-A CRISPR was significantly less than that in type I-C CRISPR and non-CRISPR strains. However, there was no statistical difference between the average number of prophages in type I-C strains and that in non-CRISPR strains. CONCLUSIONS: Our results indicated that type II-A CRISPR may play an important role in eliminating phages and that the prophage integration site may be an important criterion for the acceptance of foreign DNA by GAS. M type, spacer sequence, and prophage group data were correlated with the phylogenetic relationships of GAS. Therefore, we hypothesize that genetic characteristics and/or phylogenetic relationships of GAS may be estimated by analyzing its spacer sequences.

Pelagiphages in the Podoviridae family integrate into host genomes.

The Pelagibacterales order (SAR11) in Alphaproteobacteria dominates marine surface bacterioplankton communities, where it plays a key role in carbon and nutrient cycling. SAR11 phages, known as pelagiphages, are among the most abundant phages in the ocean. Four pelagiphages that infect Pelagibacter HTCC1062 have been reported. Here, we report 11 new pelagiphages in the Podoviridae family. Comparative genomics classified these pelagiphages into the HTVC019Pvirus genus, which includes the previously reported pelagiphages HTVC011P and HTVC019P. Phylogenomic analysis clustered HTVC019Pvirus pelagiphages into three subgroups. Integrases were identified in all but one HTVC019Pvirus genome. Site-specific integration of HTVC019Pvirus pelagiphages into host tRNA genes was verified experimentally, demonstrating the capacity of these pelagiphages to propagate by both lytic and lysogenic infection. Evidence of pelagiphage integration was also retrieved from the Global Ocean Survey database, showing that prophages are found in natural SAR11 populations. HTVC019Pvirus pelagiphages could impact SAR11 populations by a variety of mechanisms, including mortality, genetic transduction and prophage-induced viral immunity. HTVC019Pvirus pelagiphages are a rare example of cultured lysogenic phage that can be implicated in ecological processes on broad scales. These pelagiphages have the potential to become a useful model for investigating strategies of host infection and phage-dependent horizontal gene transfer.

Comparative Genomics and Characterization of the Late Promoter pR' from Shiga Toxin Prophages in Escherichia coli.

Shiga-toxin producing Escherichia coli (STEC) causes human illness ranging from mild diarrhea to death. The bacteriophage encoded stx genes are located in the late transcription region, downstream of the antiterminator Q. The transcription of the stx genes is directly under the control of the late promoter pR', thus the sequence diversity of the region between Q and stx, here termed the pR' region, may affect Stx toxin production. Here, we compared the gene structure of the pR' region and the stx subtypes of nineteen STECs. The sequence alignment and phylogenetic analysis suggested that the pR' region tends to be more heterogeneous than the promoter itself, even if the prophages harbor the same stx subtype. Furthermore, we established and validated transcriptional fusions of the pR' region to the DsRed reporter gene using mitomycin C (MMC) induction. Finally, these constructs were transformed into native and non-native strains and examined with flow cytometry. The results showed that induction levels changed when pR' regions were placed under different regulatory systems. Moreover, not every stx gene could be induced in its native host bacteria. In addition to the functional genes, the diversity of the pR' region plays an important role in determining the level of toxin induction.