Still Something to Discover: Novel Insights intoEscherichia coli Phage Diversity and Taxonomy

Isolation and characterization of a phage collection against Pseudomonas putida

The environmental bacterium, Pseudomonas putida, possesses a broad spectrum of metabolic pathways. This makes it highly promising for use in biotechnological production as a cell factory, as well as in bioremediation strategies to degrade various aromatic pollutants. For P. putida to flourish in its environment, it must withstand the continuous threats posed by bacteriophages. Interestingly, until now, only a handful of phages have been isolated for the commonly used laboratory strain, P. putida KT2440, and no phage defence mechanisms have been characterized. In this study, we present a new Collection of Environmental P. putida Phages from Estonia, or CEPEST. This collection comprises 67 double-stranded DNA phages, which belong to 22 phage species and 9 phage genera. Our findings reveal that most phages in the CEPEST collection are more infectious at lower temperatures, have a narrow host range, and require an intact lipopolysaccharide for P. putida infection. Furthermore, we show that cryptic prophages present in the P. putida chromosome provide strong protection against the infection of many phages. However, the chromosomal toxin-antitoxin systems do not play a role in the phage defence of P. putida. This research provides valuable insights into the interactions between P. putida and bacteriophages, which could have significant implications for biotechnological and environmental applications.

An essential and highly selective protein import pathway encoded by nucleus-forming phage

Targeting proteins to specific subcellular destinations is essential in prokaryotes, eukaryotes, and the viruses that infect them. Chimalliviridae phages encapsulate their genomes in a nucleus-like replication compartment composed of the protein chimallin (ChmA) that excludes ribosomes and decouples transcription from translation. These phages selectively partition proteins between the phage nucleus and the bacterial cytoplasm. Currently, the genes and signals that govern selective protein import into the phage nucleus are unknown. Here, we identify two components of this protein import pathway: a species-specific surface-exposed region of a phage intranuclear protein required for nuclear entry and a conserved protein, PicA (Protein importer of chimalliviruses A), that facilitates cargo protein trafficking across the phage nuclear shell. We also identify a defective cargo protein that is targeted to PicA on the nuclear periphery but fails to enter the nucleus, providing insight into the mechanism of nuclear protein trafficking. Using CRISPRi-ART protein expression knockdown of PicA, we show that PicA is essential early in the chimallivirus replication cycle. Together, our results allow us to propose a multistep model for the Protein Import Chimallivirus pathway, where proteins are targeted to PicA by amino acids on their surface and then licensed by PicA for nuclear entry. The divergence in the selectivity of this pathway between closely related chimalliviruses implicates its role as a key player in the evolutionary arms race between competing phages and their hosts.

An essential and highly selective protein import pathway encoded by nucleus-forming phage

Targeting proteins to specific subcellular destinations is essential in prokaryotes, eukaryotes, and the viruses that infect them. Chimalliviridae phages encapsulate their genomes in a nucleus-like replication compartment composed of the protein chimallin (ChmA) that excludes ribosomes and decouples transcription from translation. These phages selectively partition proteins between the phage nucleus and the bacterial cytoplasm. Currently, the genes and signals that govern selective protein import into the phage nucleus are unknown. Here we identify two components of this novel protein import pathway: a species-specific surface-exposed region of a phage intranuclear protein required for nuclear entry and a conserved protein, PicA, that facilitates cargo protein trafficking across the phage nuclear shell. We also identify a defective cargo protein that is targeted to PicA on the nuclear periphery but fails to enter the nucleus, providing insight into the mechanism of nuclear protein trafficking. Using CRISPRi-ART protein expression knockdown of PicA, we show that PicA is essential early in the chimallivirus replication cycle. Together our results allow us to propose a multistep model for the Protein Import Chimallivirus (PIC) pathway, where proteins are targeted to PicA by amino acids on their surface, and then licensed by PicA for nuclear entry. The divergence in the selectivity of this pathway between closely-related chimalliviruses implicates its role as a key player in the evolutionary arms race between competing phages and their hosts.

Significance Statement

The phage nucleus is an enclosed replication compartment built by Chimalliviridae phages that, similar to the eukaryotic nucleus, separates transcription from translation and selectively imports certain proteins. This allows the phage to concentrate proteins required for DNA replication and transcription while excluding DNA-targeting host defense proteins. However, the mechanism of selective trafficking into the phage nucleus is currently unknown. Here we determine the region of a phage nuclear protein that targets it for nuclear import and identify a conserved, essential nuclear shell-associated protein that plays a key role in this process. This work provides the first mechanistic model of selective import into the phage nucleus.

Complete genome of Escherichia phages Carena and JoYop

Escherichia phages Carena and JoYop were isolated from water samples in Abidjan (Cote d'Ivoire). Their genomes comprise 39,283 and 169,193 bp, encoding 44 and 246 predicted genes, respectively. Carena shares 93.4% nucleotide identity with Escherichia podophage CarlSpitteler (Berlinvirus), and JoYop shows 95.6% identity with Escherichia myophage ADUt (Tequatrovirus).

Diverse bacteriophages for biocontrol of ESBL- and AmpC-β-lactamase-producing E. coli

Novel solutions are needed to reduce the risk of transmission of extended spectrum β-lactamase (ESBL) and AmpC β-lactamase producing Escherichia coli (ESBL/AmpC E. coli) from livestock to humans. Given that phages are promising biocontrol agents, a collection of 28 phages that infect ESBL/AmpC E. coli were established. Whole genome sequencing showed that all these phages were unique and could be assigned to 15 different genera. Host range analysis showed that 82% of 198 strains, representing the genetic diversity of ESBL/AmpC E. coli, were sensitive to at least one phage. Identifying receptors used for phage binding experimentally as well as in silico predictions, allowed us to combine phages into two different cocktails with broad host range targeting diverse receptors. These phage cocktails efficiently inhibit the growth of ESBL/AmpC E. coli in vitro, thus suggesting the potential of phages as promising biocontrol agents.

Genomic and Proteomic Analysis of Six Vi01-like Phages Reveals Wide Host Range and Multiple Tail Spike Proteins

Enterobacteriaceae is a large family of Gram-negative bacteria composed of many pathogens, including Salmonella and Shigella. Here, we characterize six bacteriophages that infect Enterobacteriaceae, which were isolated from wastewater plants in the Wasatch front (Utah, United States). These phages are highly similar to the Kuttervirus vB_SenM_Vi01 (Vi01), which was isolated using wastewater from Kiel, Germany. The phages vary little in genome size and are between 157 kb and 164 kb, which is consistent with the sizes of other phages in the Vi01-like phage family. These six phages were characterized through genomic and proteomic comparison, mass spectrometry, and both laboratory and clinical host range studies. While their proteomes are largely unstudied, mass spectrometry analysis confirmed the production of five hypothetical proteins, several of which unveiled a potential operon that suggests a ferritin-mediated entry system on the Vi01-like phage family tail. However, no dependence on this pathway was observed for the single host tested herein. While unable to infect every genus of Enterobacteriaceae tested, these phages are extraordinarily broad ranged, with several demonstrating the ability to infect Salmonella enterica and Citrobacter freundii strains with generally high efficiency, as well as several clinical Salmonella enterica isolates, most likely due to their multiple tail fibers.

Recent Progress in Phage-Based Nanoplatforms for Tumor Therapy

Nanodrug delivery systems have demonstrated a great potential for tumor therapy with the development of nanotechnology. Nonetheless, traditional drug delivery systems are faced with issues such as complex synthetic procedures, low reproducibility, nonspecific distribution, impenetrability of biological barrier, systemic toxicity, etc. In recent years, phage-based nanoplatforms have attracted increasing attention in tumor treatment for their regular structure, fantastic carrying property, high transduction efficiency and biosafety. Notably, therapeutic or targeting peptides can be expressed on the surface of the phages through phage display technology, enabling the phage vectors to possess multifunctions. As a result, the drug delivery efficiency on tumor will be vastly improved, thereby enhancing the therapeutic efficacy while reducing the side effects on normal tissues. Moreover, phages can overcome the hindrance of biofilm barrier to elicit antitumor effects, which exhibit great advantages compared with traditional synthetic drug delivery systems. Herein, this review not only summarizes the structure and biology of the phages, but also presents their potential as prominent nanoplatforms against tumor in different pathways to inspire the development of effective nanomedicine.

Circulation of adenovirus and other viruses in urban drainage channels: an environmental surveillance in Belém, Amazon region, Brazil

Urban channels in amazon cities are very polluted, with garbage and sewage disposal in these aquatic environments, favoring the high dissemination of waterborne viruses such as human adenovirus (HAdV). The aim of this study was to perform the detection and molecular characterization of adenovirus in urban channels and in a wastewater treatment plant located in a metropolitan city in the Amazon. Additionally, metagenomic analyses were performed to assess viral diversity. Samples were concentrated by organic flocculation, analyzed by quantitative real time PCR (qPCR) and sequenced (Sanger e next generation sequencing). Cell culture was performed to verify the viability of HAdV particles. A total of 104 samples were collected, being the HAdV positivity of 76% (79/104). Among the positive samples, 29.1% (23/79) were characterized as HAdV-F40 (87%, 20/23), HAdV-F41 (8.7%, 2/23), and HAdV-B (4.3%, 1/23). Average precipitation rates ranged from 163 to 614 mm, while the pH ranged from 6.9 to 7.6. Eight positive samples were inoculated into A549 cells and in 4 of these, was observed changes in the structure of the cell monolayer, alteration in the structure of the cell monolayer was observed, but without amplification when analyzed by PCR. The metagenomic data demonstrated the presence of 14 viral families, being the most abundant: Myoviridae (41% of available reads), Siphoviridae (24.5%), Podoviridae (14.1%), and Autographiviridae (6.9%) with more than 85% of the total number of identified reads. This study reinforcing that continuous surveillance may contribute to monitoring viral diversity in aquatic environments and provide early warning of potential outbreaks.

Characterization of phage vB_EcoS-EE09 infecting E. coli DSM613 Isolated from Wastewater Treatment Plant Effluent and Comparative Proteomics of the Infected and Non-Infected Host

Phages influence microbial communities, can be applied in phage therapy, or may serve as bioindicators, e.g., in (waste)water management. We here characterized the Escherichia phage vB_EcoS-EE09 isolated from an urban wastewater treatment plant effluent. Phage vB_EcoS-EE09 belongs to the genus Dhillonvirus, class Caudoviricetes. It has an icosahedral capsid with a long non-contractile tail and a dsDNA genome with an approximate size of 44 kb and a 54.6% GC content. Phage vB_EcoS-EE09 infected 12 out of the 17 E. coli strains tested. We identified 16 structural phage proteins, including the major capsid protein, in cell-free lysates by protein mass spectrometry. Comparative proteomics of protein extracts of infected E. coli cells revealed that proteins involved in amino acid and protein metabolism were more abundant in infected compared to non-infected cells. Among the proteins involved in the stress response, 74% were less abundant in the infected cultures compared to the non-infected controls, with six proteins showing significant less abundance. Repressing the expression of these proteins may be a phage strategy to evade host defense mechanisms. Our results contribute to diversifying phage collections, identifying structural proteins to enable better reliability in annotating taxonomically related phage genomes, and understanding phage-host interactions at the protein level.

Diverse Durham collection phages demonstrate complex BREX defense responses

Bacteriophages (phages) outnumber bacteria ten-to-one and cause infections at a rate of 1025 per second. The ability of phages to reduce bacterial populations makes them attractive alternative antibacterials for use in combating the rise in antimicrobial resistance. This effort may be hindered due to bacterial defenses such as Bacteriophage Exclusion (BREX) that have arisen from the constant evolutionary battle between bacteria and phages. For phages to be widely accepted as therapeutics in Western medicine, more must be understood about bacteria-phage interactions and the outcomes of bacterial phage defense. Here, we present the annotated genomes of 12 novel bacteriophage species isolated from water sources in Durham, UK, during undergraduate practical classes. The collection includes diverse species from across known phylogenetic groups. Comparative analyses of two novel phages from the collection suggest they may be founding members of a new genus. Using this Durham phage collection, we determined that particular BREX defense systems were likely to confer a varied degree of resistance against an invading phage. We concluded that the number of BREX target motifs encoded in the phage genome was not proportional to the degree of susceptibility. IMPORTANCE Bacteriophages have long been the source of tools for biotechnology that are in everyday use in molecular biology research laboratories worldwide. Phages make attractive new targets for the development of novel antimicrobials. While the number of phage genome depositions has increased in recent years, the expected bacteriophage diversity remains underrepresented. Here we demonstrate how undergraduates can contribute to the identification of novel phages and that a single City in England can provide ample phage diversity and the opportunity to find novel technologies. Moreover, we demonstrate that the interactions and intricacies of the interplay between bacterial phage defense systems such as Bacteriophage Exclusion (BREX) and phages are more complex than originally thought. Further work will be required in the field before the dynamic interactions between phages and bacterial defense systems are fully understood and integrated with novel phage therapies.

Metagenomic investigation reveals bacteriophage-mediated horizontal transfer of antibiotic resistance genes in microbial communities of an organic agricultural ecosystem

Agricultural microbiomes are major reservoirs of antibiotic resistance genes (ARGs), posing continuous risks to human health. To understand the role of bacteriophages as vehicles for the horizontal transfer of ARGs in the agricultural microbiome, we investigated the diversity of bacterial and viral microbiota from fecal and environmental samples on an organic farm. The profiles of the microbiome indicated the highest abundance of Bacteroidetes, Firmicutes, and Proteobacteria phyla in animal feces, with varying Actinobacteria and Spirochaetes abundance across farm animals. The most predominant composition in environmental samples was the phylum Proteobacteria. Compared to the microbiome profiles, the trends in virome indicated much broader diversity with more specific signatures between the fecal and environmental samples. Overall, viruses belonging to the order Caudovirales were the most prevalent across the agricultural samples. Additionally, the similarities within and between fecal and environmental components of the agricultural environment based on ARG-associated bacteria alone were much lower than those of total microbiome composition. However, there were significant similarities in the profiles of ARG-associated viruses across the fecal and environmental components. Moreover, the predictive models of phage-bacterial interactions on bipartite ARG transfer networks indicated that phages belonging to the order Caudovirales, particularly in the Siphoviridae family, contained diverse ARG types in different samples. Their interaction with various bacterial hosts further implied the important role of bacteriophages in ARG transmission across bacterial populations. Our findings provided a novel insight into the potential mechanisms of phage-mediated ARG transmission and their correlation with resistome evolution in natural agricultural environments. IMPORTANCE Antibiotic resistance has become a serious health concern worldwide. The potential impact of viruses, bacteriophages in particular, on spreading antibiotic resistance genes is still controversial due to the complexity of bacteriophage-bacterial interactions within diverse environments. In this study, we determined the microbiome profiles and the potential antibiotic resistance gene (ARG) transfer between bacterial and viral populations in different agricultural samples using a high-resolution analysis of the metagenomes. The results of this study provide compelling genetic evidence for ARG transfer through bacteriophage-bacteria interactions, revealing the inherent risks associated with bacteriophage-mediated ARG transfer across the agricultural microbiome.

Bacteriophages for the Targeted Control of Foodborne Pathogens

Foodborne illness is exacerbated by novel and emerging pathotypes, persistent contamination, antimicrobial resistance, an ever-changing environment, and the complexity of food production systems. Sporadic and outbreak events of common foodborne pathogens like Shiga toxigenic E. coli (STEC), Salmonella, Campylobacter, and Listeria monocytogenes are increasingly identified. Methods of controlling human infections linked with food products are essential to improve food safety and public health and to avoid economic losses associated with contaminated food product recalls and litigations. Bacteriophages (phages) are an attractive additional weapon in the ongoing search for preventative measures to improve food safety and public health. However, like all other antimicrobial interventions that are being employed in food production systems, phages are not a panacea to all food safety challenges. Therefore, while phage-based biocontrol can be promising in combating foodborne pathogens, their antibacterial spectrum is generally narrower than most antibiotics. The emergence of phage-insensitive single-cell variants and the formulation of effective cocktails are some of the challenges faced by phage-based biocontrol methods. This review examines phage-based applications at critical control points in food production systems with an emphasis on when and where they can be successfully applied at production and processing levels. Shortcomings associated with phage-based control measures are outlined together with strategies that can be applied to improve phage utility for current and future applications in food safety.

Phages for treatment of Escherichia coli infections

Diseases due to infections by pathogenic Escherichia coli strains are on the rise and with the growing antimicrobial resistance among bacterial pathogens, including this group. Thus, alternative therapeutic options are actively investigated. Among these alternatives is phage therapy. In the case of E. coli, the combination of the well understood biology of this species and its bacteriophages represents a good guiding example for the establishment of phage therapy principles against this and other pathogenic bacteria. In this chapter, the procedures toward the development of phage therapy against pathogenic E. coli with the use of T-even group of phages are discussed. These steps involve the isolation, purification, characterisation and large-scale production of these phages, with formulation of phage cocktails for in vitro and in vivo studies. The main emphasis is made on phage therapy of enteropathogenic E. coli O157:H, which is one of the prominent human pathogens but persists as a commensal bacterium in many food animals. The implementation of phage therapy against E. coli O157:H within the One Health framework in carrier animals and for treatment of meat, vegetables, fruits and other agricultural produce thus would allow controlling and interrupting the transmission routes of this pathogen to the human food chain and preventing human disease. Examples of successful control and elimination of E. coli O157:H are given, while the problems encountered in phage treatment of this pathogen are also discussed.

Isolation and Characterization of a Novel Phage Collection against Avian-Pathogenic Escherichia coli

The increase in antibiotic-resistant avian-pathogenic Escherichia coli (APEC), the causative agent of colibacillosis in poultry, warrants urgent research and the development of alternative therapies. This study describes the isolation and characterization of 19 genetically diverse, lytic coliphages, 8 of which were tested in combination for their efficacy in controlling in ovo APEC infections. Genome homology analysis revealed that the phages belong to nine different genera, one of them being a novel genus (Nouzillyvirus). One phage, REC, was derived from a recombination event between two Phapecoctavirus phages (ESCO5 and ESCO37) isolated in this study. Twenty-six of the 30 APEC strains tested were lysed by at least one phage. Phages exhibited varying infectious capacities, with narrow to broad host ranges. The broad host range of some phages could be partially explained by the presence of receptor-binding protein carrying a polysaccharidase domain. To demonstrate their therapeutic potential, a phage cocktail consisting of eight phages belonging to eight different genera was tested against BEN4358, an APEC O2 strain. In vitro, this phage cocktail fully inhibited the growth of BEN4358. In a chicken lethality embryo assay, the phage cocktail enabled 90% of phage-treated embryos to survive infection with BEN4358, compared with 0% of nontreated embryos, indicating that these novel phages are good candidates to successfully treat colibacillosis in poultry. IMPORTANCE Colibacillosis, the most common bacterial disease affecting poultry, is mainly treated by antibiotics. Due to the increased prevalence of multidrug-resistant avian-pathogenic Escherichia coli, there is an urgent need to assess the efficacy of alternatives to antibiotherapy, such as phage therapy. Here, we have isolated and characterized 19 coliphages that belong to nine phage genera. We showed that a combination of 8 of these phages was efficacious in vitro to control the growth of a clinical isolate of E. coli. Used in ovo, this phage combination allowed embryos to survive APEC infection. Thus, this phage combination represents a promising treatment for avian colibacillosis.

Characterization and Comparative Genomic Analysis of Three Virulent E. coli Bacteriophages with the Potential to Reduce Antibiotic-Resistant Bacteria in the Environment

The emerging global crisis of antibiotic resistance demands new alternative antibacterial solutions. Although bacteriophages have been used to combat bacterial infections for over a century, a dramatic boost in phage studies has recently been observed. In the development of modern phage applications, a scientific rationale is strongly required and newly isolated phages need to be examined in detail. In this study, we present the full characterization of bacteriophages BF9, BF15, and BF17, with lytic activity against extended-spectrum β-lactamases (ESBLs)- and AmpC β-lactamases (AmpC)-producing Escherichia coli, the prevalence of which has increased significantly in livestock in recent decades, representing a great hazard to food safety and a public health risk. Comparative genomic and phylogenetic analysis indicated that BF9, BF15, and BF17 represent the genera Dhillonvirus, Tequatrovirus, and Asteriusvirus, respectively. All three phages significantly reduced in vitro growth of their bacterial host and retained the ability to lyse bacteria after preincubation at wide ranges of temperature (−20–40 °C) and pH (5–9). The results described herein indicate the lytic nature of BF9, BF15, and BF17, which, along with the absence of genes encoding toxins and bacterial virulence factors, represents an undoubted asset in terms of future phage application.

Expansion of Kuravirus-like Phage Sequences within the Past Decade, including Escherichia Phage YF01 from Japan, Prompt the Creation of Three New Genera

Bacteriophages, viruses that infect bacteria, are currently receiving significant attention amid an ever-growing global antibiotic resistance crisis. In tandem, a surge in the availability and affordability of next-generation and third-generation sequencing technologies has driven the deposition of a wealth of phage sequence data. Here, we have isolated a novel Escherichia phage, YF01, from a municipal wastewater treatment plant in Yokohama, Japan. We demonstrate that the YF01 phage shares a high similarity to a collection of thirty-five Escherichia and Shigella phages found in public databases, six of which have been previously classified into the Kuravirus genus by the International Committee on Taxonomy of Viruses (ICTV). Using modern phylogenetic approaches, we demonstrate that an expansion and reshaping of the current six-membered Kuravirus genus is required to accommodate all thirty-six member phages. Ultimately, we propose the creation of three additional genera, Vellorevirus, Jinjuvirus, and Yesanvirus, which will allow a more organized approach to the addition of future Kuravirus-like phages.

A Flexible and Efficient Microfluidics Platform for the Characterization and Isolation of Novel Bacteriophages

Bacteriophages are viruses that infect bacteria. This property makes them highly suitable for varied uses in industry or in the development of the treatment of bacterial infections. However, the conventional methods that are used to isolate and analyze these bacteriophages from the environment are generally cumbersome and time consuming. Here, we adapted a high-throughput microfluidic setup for long-term analysis of bacteriophage-bacteria interaction and demonstrate isolation of phages from environmental samples. IMPORTANCE Bacteriophages are gaining increased attention for their potential application as agents to combat antibiotic-resistant infections. However, isolation and characterization of new phages are time consuming and limited by currently used methods. The microfluidics platform presented here allows the isolation and long-term analysis of phages and their effect on host cells with fluorescent light microscopy imaging. Furthermore, this new workflow allows high-throughput characterization of environmental samples for the identification of phages alongside gaining detailed insight into the host response. Taken together, this microfluidics platform will be a valuable tool for phage research, enabling faster and more efficient screening and characterization of host-phage interactions.

A Klebsiella pneumoniae NDM-1+ bacteriophage: Adaptive polyvalence and disruption of heterogenous biofilms

Bacteriophage KL-2146 is a lytic virus isolated to infect Klebsiella pneumoniae BAA2146, a pathogen carrying the broad range antibiotic resistance gene New Delhi metallo-betalactamase-1 (NDM-1). Upon complete characterization, the virus is shown to belong to the Drexlerviridae family and is a member of the Webervirus genus located within the (formerly) T1-like cluster of phages. Its double-stranded (dsDNA) genome is 47,844 bp long and is predicted to have 74 protein-coding sequences (CDS). After challenging a variety of K. pneumoniae strains with phage KL-2146, grown on the NDM-1 positive strain BAA-2146, polyvalence was shown for a single antibiotic-sensitive strain, K. pneumoniae 13,883, with a very low initial infection efficiency in liquid culture. However, after one or more cycles of infection in K. pneumoniae 13,883, nearly 100% infection efficiency was achieved, while infection efficiency toward its original host, K. pneumoniae BAA-2146, was decreased. This change in host specificity is reversible upon re-infection of the NDM-1 positive strain (BAA-2146) using phages grown on the NDM-1 negative strain (13883). In biofilm infectivity experiments, the polyvalent nature of KL-2146 was demonstrated with the killing of both the multidrug-resistant K. pneumoniae BAA-2146 and drug-sensitive 13,883 in a multi-strain biofilm. The ability to infect an alternate, antibiotic-sensitive strain makes KL-2146 a useful model for studying phages infecting the NDM-1+ strain, K. pneumoniae BAA-2146. GRAPHICAL ABSTRACT.

Genomic Profiling of Non-O157 Shiga Toxigenic Escherichia coli-Infecting Bacteriophages from South Africa

Background

Non-O157 Shiga toxigenic Escherichia coli (STEC) are one of the most important food and waterborne pathogens worldwide. Although bacteriophages (phages) have been used for the biocontrol of these pathogens, a comprehensive understanding of the genetic characteristics and lifestyle of potentially effective candidate phages is lacking.

Materials and Methods

In this study, 10 non-O157-infecting phages previously isolated from feedlot cattle and dairy farms in the North-West province of South Africa were sequenced, and their genomes were analyzed.

Results

Comparative genomics and proteomics revealed that the phages were closely related to other E. coli-infecting Tunaviruses, Seuratviruses, Carltongylesviruses, Tequatroviruses, and Mosigviruses from the National Center for Biotechnology Information GenBank database. Phages lacked integrases associated with a lysogenic cycle and genes associated with antibiotic resistance and Shiga toxins.

Conclusions

Comparative genomic analysis identified a diversity of unique non-O157-infecting phages, which could be used to mitigate the abundance of various non-O157 STEC serogroups without safety concerns.

Toothpicks, logic, and next-generation sequencing: systematic investigation of bacteriophage-host interactions

Bacteriophages are abundant and diverse predators that drive community dynamics in many ecosystems and hold great potential for biotechnology and as therapeutics for bacterial infections. Previous research has largely explored phage-host interactions one-by-one, which limited our ability to observe phenotypic patterns, to uncover their genetic basis, and to unravel the underlying molecular mechanisms. However, the famous 'toothpicks and logic' were recently joined by large-scale sequencing of phage genomes and bacterial genome-wide screens that enable us to systematically investigate phage-host interactions. In this article, we highlight recent breakthroughs from the molecular basis of phage host range and receptor recognition over new insights into bacterial immunity to the serendipitous discovery of a new bacterial surface glycan. Future work will enable the understanding, prediction, and engineering of more complicated phage traits for new applications and extend the scope of these studies from simple test tube experiments to natural communities of phages and hosts.

Isolation and Characterization of Lytic Bacteriophages Active against Clinical Strains of E. coli and Development of a Phage Antimicrobial Cocktail

Pathogenic E. coli cause urinary tract, soft tissue and central nervous system infections, sepsis, etc. Lytic bacteriophages can be used to combat such infections. We investigated six lytic E. coli bacteriophages isolated from wastewater. Transmission electron microscopy and whole genome sequencing showed that the isolated bacteriophages are tailed phages of the Caudoviricetes class. One-step growth curves revealed that their latent period of reproduction is 20-30 min, and the average value of the burst size is 117-155. During co-cultivation with various E. coli strains, the phages completely suppressed bacterial host culture growth within the first 4 h at MOIs 10^-7 to 10^-3. The host range lysed by each bacteriophage varied from six to two bacterial strains out of nine used in the study. The cocktail formed from the isolated bacteriophages possessed the ability to completely suppress the growth of all the E. coli strains used in the study within 6 h and maintain its lytic activity for 8 months of storage. All the isolated bacteriophages may be useful in fighting pathogenic E. coli strains and in the development of phage cocktails with a long storage period and high efficiency in the treatment of bacterial infections.

Isolation, Characterization, and Genome Analysis of a Novel Bacteriophage, Escherichia Phage vB_EcoM-4HA13, Representing a New Phage Genus in the Novel Phage Family Chaseviridae

Shiga toxin-producing Escherichia coli (STEC) is one of the leading causes of foodborne illnesses in North America and can lead to severe symptoms, with increased fatality risk for young children. While E. coli O157:H7 remains the dominant STEC serotype associated with foodborne outbreaks, there has been an increasing number of non-O157 STEC outbreaks in recent years. For the food industry, lytic bacteriophages offer an organic, self-limiting alternative to pathogen reduction-one that could replace or reduce the use of chemical and physical food processing methods. From EHEC-enriched sewage, we isolated a novel bacteriophage, vB_EcoM-4HA13 (4HA13). Phenotypic characterizations revealed 4HA13 to possess a myoviral morphotype, with a high specificity to non-motile O111 serotype, and a long latent period (90 min). Through genomic analyses, this 52,401-bp dsDNA phage was found to contain 81 CDS, but no detectable presence of antibiotic resistance, integrase, or virulence genes. A BLASTn search for each of the identified 81 CDS yielded homologues with low levels of similarity. Comparison of RNA polymerase and terminase large subunit amino acid sequences led to the proposal and acceptance of a new bacteriophage family, Chaseviridae, with 4HA13 representing a new species and genus. The discovery of this phage has broadened our current knowledge of bacteriophage diversity.

Genome Sequences of 16 Escherichia coli Bacteriophages Isolated from Wastewater, Pond Water, Cow Manure, and Bird Feces

Escherichia coli is a highly diverse bacterial species comprising both commensal and pathogenic strains. Here, we report complete genome sequences of 16 E. coli bacteriophages isolated from various environmental samples using the ECOR collection as isolation hosts.

Novel findings in context of molecular diversity and abundance of bacteriophages in wastewater environments of Riyadh, Saudi Arabia

The diversity among bacteriophages depends on different factors like ecology, temperature conditions and genetic pool. Current study focused on isolation, identification and diversity of phages from 34 sewage water samples collected from two different wastewater treatment plants (WWTPs), King Saud University wastewater treatment plants (KSU-WWTP) and Manfoha wastewater treatment plants (MN-WWTP) in Riyadh, Saudi Arabia. Samples were analyzed by PCR and Next Generation Sequencing (NGS). Siphoviridae, Podoviridae and Myoviridae families were detected by family-specific PCR and highest prevalence of Myoviridae 29.40% was found at MN-WWTP followed by 11.76% at KSU-WWTP. Siphoviridae was detected 11.76% at MN-WWTP and 5.88% at KSU-WWTP. Lowest prevalence for Podoviridae family (5.88%) was recorded at MN-WWTP. Significant influence of temporal variations on prevalence of Myoviridae and Siphoviridae was detected in both WWTP and MN-WWTP, respectively. Highest phage prevalence was obtained in August (75%), followed by September (50%). Highest phage prevalence was recorded at a temperature range of 29–33°C. Significant influence of temperature on the prevalence of Myoviridae phages was detected at MN-WWTP. Four bacteriophages with various abundance levels were identified by NGS. Cronobacter virus Esp2949-1 was found first time with highest abundance (4.41%) in wastewater of Riyadh. Bordetella virus BPP1 (4.14%), Dickeya virus Limestone (1.55%) and Ralstonia virus RSA1 (1.04%) were also detected from samples of MN-WWTP. Highest occurrence of Bordetella virus BPP1 (67%) and (33.33%) was recorded at KSU-WWTP and MN-WWTP, respectively. Highest Bordetella virus BPP1 occurrence was recorded in September (50%) followed by August (40%). The findings of study showed new insights of phage diversity from wastewater sources and further large-scale data studies are suggested for comprehensive understanding.

A cytoskeletal vortex drives phage nucleus rotation during jumbo phage replication in E. coli

Nucleus-forming jumbo phages establish an intricate subcellular organization, enclosing phage genomes within a proteinaceous shell called the phage nucleus. During infection in Pseudomonas, some jumbo phages assemble a bipolar spindle of tubulin-like PhuZ filaments that positions the phage nucleus at midcell and drives its intracellular rotation. This facilitates the distribution of capsids on its surface for genome packaging. Here we show that the Escherichia coli jumbo phage Goslar assembles a phage nucleus surrounded by an array of PhuZ filaments resembling a vortex instead of a bipolar spindle. Expression of a mutant PhuZ protein strongly reduces Goslar phage nucleus rotation, demonstrating that the PhuZ cytoskeletal vortex is necessary for rotating the phage nucleus. While vortex-like cytoskeletal arrays are important in eukaryotes for cytoplasmic streaming and nucleus alignment, this work identifies a coherent assembly of filaments into a vortex-like structure driving intracellular rotation within the prokaryotic cytoplasm.

Coliphages as viral indicators of sanitary significance for drinking water

Coliphages are virus that infect coliform bacteria and are used in aquatic systems for risk assessment for human enteric viruses. This mini-review appraises the types and sources of coliphage and their fate and behavior in source waters and engineered drinking water treatment systems. Somatic (cell wall infection) and F+ (male specific) coliphages are abundant in drinking water sources and are used as indicators of fecal contamination. Coliphage abundances do not consistently correlate to human enteric virus abundance, but they suitably reflect the risks of exposure to human enteric viruses. Coliphages have highly variable surface characteristics with respect to morphology, size, charge, isoelectric point, and hydrophobicity which together interact to govern partitioning and removal characteristics during water treatment. The groups somatic and F+ coliphages are valuable for investigating the virus elimination during water treatment steps and as indicators for viral water quality assessment. Strain level analyses (e.g., Qβ or GA-like) provide more information about specific sources of viral pollution but are impractical for routine monitoring. Consistent links between rapid online monitoring tools (e.g., turbidity, particle counters, and flow cytometry) and phages in drinking water have yet to be established but are recommended as a future area of research activity. This could enable the real-time monitoring of virus and improve the process understanding during transient operational events. Exciting future prospects for the use of coliphages in aquatic microbiology are also discussed based on current scientific evidence and practical needs.

Impact of a phage cocktail targeting Escherichia coli and Enterococcus faecalis as members of a gut bacterial consortium in vitro and in vivo

Escherichia coli and Enterococcus faecalis have been implicated as important players in human gut health that have been associated with the onset of inflammatory bowel disease (IBD). Bacteriophage (phage) therapy has been used for decades to target pathogens as an alternative to antibiotics, but the ability of phage to shape complex bacterial consortia in the lower gastrointestinal tract is not clearly understood. We administered a cocktail of six phages (either viable or heat-inactivated) targeting pro-inflammatory Escherichia coli LF82 and Enterococcus faecalis OG1RF as members of a defined community in both a continuous fermenter and a murine colitis model. The two target strains were members of a six species simplified human microbiome consortium (SIHUMI-6). In a 72-h continuous fermentation, the phage cocktail caused a 1.1 and 1.5 log (log10 genome copies/mL) reduction in E. faecalis and E. coli numbers, respectively. This interaction was accompanied by changes in the numbers of other SIHUMI-6 members, with an increase of Lactiplantibacillus plantarum (1.7 log) and Faecalibacterium prausnitzii (1.8 log). However, in germ-free mice colonized by the same bacterial consortium, the same phage cocktail administered twice a week over nine weeks did not cause a significant reduction of the target strains. Mice treated with active or inactive phage had similar levels of pro-inflammatory cytokines (IFN-y/IL12p40) in unstimulated colorectal colonic strip cultures. However, histology scores of the murine lower GIT (cecum and distal colon) were lower in the viable phage-treated mice, suggesting that the phage cocktail did influence the functionality of the SIHUMI-6 consortium. For this study, we conclude that the observed potential of phages to reduce host populations in in vitro models did not translate to a similar outcome in an in vivo setting, with this effect likely brought about by the reduction of phage numbers during transit of the mouse GIT.

PhageCocktail: An R package to design phage cocktails from experimental phage-bacteria infection networks

BACKGROUND AND OBJECTIVE

Phage therapy is a resurgent strategy used in medicine and the food industry to lyse bacteria that cause damage to health or spoil a food product. Frequently, phage-bacteria infection networks have a large size, making it impossible to manually study all possible phage cocktails. Thus, this article presents an R package called PhageCocktail to automatically design efficient phage cocktails from phage-bacteria infection networks.

METHODS

This R package includes four different methods for designing phage cocktails: ExhaustiveSearch, ExhaustivePhi, ClusteringSearch, and ClusteringPhi. These four methods are explained in detail and are evaluated using 13 empirical phage-bacteria infection networks. More specifically, runtime and expected success (fraction of lysed bacteria) are analyzed.

RESULTS

The four methods have variations in terms of runtime and quality of the results. ExhaustiveSearch always provides the best possible phage cocktail, but its runtime could be long. ExhaustivePhi only focuses on one cocktail size, the one estimated as the best; thus, its runtime is less than ExhaustiveSearch, but it can produce cocktails with more phages than necessary. ClusteringSearch and ClusteringPhi are very fast (generally, less than one millisecond), providing always immediate results due to clustering techniques, but their accuracies can be lower, yielding cocktails with lower expected successes.

CONCLUSIONS

The larger the phage-bacteria infection network is, the more complex its analysis is. Thus, this tool eases this task for scientists and other users while designing phage cocktails of good quality. This R package includes four different methods; therefore, users may choose among them, considering their preferences in speed and accuracy of results.

Isolation and characterization of Escherichia coli O157: H7 novel bacteriophage for controlling this food-borne pathogen

Escherichia coli O157: H7 is known as a high-risk food-born pathogen, and its removal is vital for maintaining food safety. The increasing trend of food-borne diseases caused by this bacterium and other pathogens indicates the low efficiency of the methods to remove pathogens from foodstuffs. One of the new and effective methods is to use of a bio-control agent called bacteriophage, which has shown good function in eliminating and reducing pathogens. In this study, a novel bacteriophage was isolated and identified from the slaughterhouse wastewater to control E. coli O157: H7. This bacteriophage belonged to the Myoviridae family. Two bacterial genera including E. coli and Salmonella, were allocated to determine the bacteriophage host range; the result showed that the anti- Salmonella effect of phage was low. The phage was stable at high temperature (80°C) and caused an acceptable reduction in the E. coli O157: H7 (4.18 log CFU / mL for 10 hours). The isolated bacteriophage was corroborated to be completely safe based on the whole genome sequencing and lack of any virulence factor from the host bacteria. Considering the characteristics of this phage and its function in vitro, this bacteriophage may be used as an effective bio-control agent in foods with the possible E. coli O157: H7 -induced contamination.

Computational design of phage cocktails based on phage-bacteria infection networks

The misuse and overuse of antibiotics have boosted the proliferation of multidrug-resistant (MDR) bacteria, which are considered a major public health issue in the twenty-first century. Phage therapy may be a promising way in the treatment of infections caused by MDR pathogens, without the side effects of the current available antimicrobials. Phage therapy is based on phage cocktails, that is, combinations of phages able to lyse the target bacteria. In this work, we present and explain in detail two innovative computational methods to design phage cocktails taking into account a given phage-bacteria infection network. One of the methods (Exhaustive Search) always generates the best possible phage cocktail, while the other method (Network Metrics) always keeps a very reduced runtime (a few milliseconds). Both methods have been included in a Cytoscape application that is available for any user. A complete experimental study has been performed, evaluating and comparing the biological quality, runtime, and the impact when additional phages are included in the cocktail.

Broad-spectrum CRISPR-Cas13a enables efficient phage genome editing

CRISPR-Cas13 proteins are RNA-guided RNA nucleases that defend against incoming RNA and DNA phages by binding to complementary target phage transcripts followed by general, non-specific RNA degradation. Here we analysed the defensive capabilities of LbuCas13a from Leptotrichia buccalis and found it to have robust antiviral activity unaffected by target phage gene essentiality, gene expression timing or target sequence location. Furthermore, we find LbuCas13a antiviral activity to be broadly effective against a wide range of phages by challenging LbuCas13a against nine E. coli phages from diverse phylogenetic groups. Leveraging the versatility and potency enabled by LbuCas13a targeting, we applied LbuCas13a towards broad-spectrum phage editing. Using a two-step phage-editing and enrichment method, we achieved seven markerless genome edits in three diverse phages with 100% efficiency, including edits as large as multi-gene deletions and as small as replacing a single codon. Cas13a can be applied as a generalizable tool for editing the most abundant and diverse biological entities on Earth.

Natural Bred ε2-Phages Have an Improved Host Range and Virulence against Uropathogenic Escherichia coli over Their Ancestor Phages

Alternative treatments for Escherichia coli infections are urgently needed, and phage therapy is a promising option where antibiotics fail, especially for urinary tract infections (UTI). We used wastewater-isolated phages to test their lytic activity against a panel of 47 E. coli strains reflecting the diversity of strains found in UTI, including sequence type 131, 73 and 69. The plaquing host range (PHR) was between 13 and 63%. In contrast, the kinetic host range (KHR), describing the percentage of strains for which growth in suspension was suppressed for 24 h, was between 0% and 19%, substantially lower than the PHR. To improve the phage host range and their efficacy, we bred the phages by mixing and propagating cocktails on a subset of E. coli strains. The bred phages, which we termed evolution-squared ε2-phages, of a mixture of Myoviridae have KHRs up to 23% broader compared to their ancestors. Furthermore, using constant phage concentrations, Myoviridae ε2-phages suppressed the growth of higher bacterial inocula than their ancestors did. Thus, the ε2-phages were more virulent compared to their ancestors. Analysis of the genetic sequences of the ε2-phages with the broadest host range reveals that they are mosaic intercrossings of 2-3 ancestor phages. The recombination sites are distributed over the whole length of the genome. All ε2-phages are devoid of genes conferring lysogeny, antibiotic resistance, or virulence. Overall, this study shows that ε2-phages are remarkably more suitable than the wild-type phages for phage therapy.

Systematic exploration of Escherichia coli phage-host interactions with the BASEL phage collection

Bacteriophages, the viruses infecting bacteria, hold great potential for the treatment of multidrug-resistant bacterial infections and other applications due to their unparalleled diversity and recent breakthroughs in their genetic engineering. However, fundamental knowledge of the molecular mechanisms underlying phage-host interactions is mostly confined to a few traditional model systems and did not keep pace with the recent massive expansion of the field. The true potential of molecular biology encoded by these viruses has therefore remained largely untapped, and phages for therapy or other applications are often still selected empirically. We therefore sought to promote a systematic exploration of phage-host interactions by composing a well-assorted library of 68 newly isolated phages infecting the model organism Escherichia coli that we share with the community as the BASEL (BActeriophage SElection for your Laboratory) collection. This collection is largely representative of natural E. coli phage diversity and was intensively characterized phenotypically and genomically alongside 10 well-studied traditional model phages. We experimentally determined essential host receptors of all phages, quantified their sensitivity to 11 defense systems across different layers of bacterial immunity, and matched these results to the phages' host range across a panel of pathogenic enterobacterial strains. Clear patterns in the distribution of phage phenotypes and genomic features highlighted systematic differences in the potency of different immunity systems and suggested the molecular basis of receptor specificity in several phage groups. Our results also indicate strong trade-offs between fitness traits like broad host recognition and resistance to bacterial immunity that might drive the divergent adaptation of different phage groups to specific ecological niches. We envision that the BASEL collection will inspire future work exploring the biology of bacteriophages and their hosts by facilitating the discovery of underlying molecular mechanisms as the basis for an effective translation into biotechnology or therapeutic applications.

Inhibition of Antimicrobial-Resistant Escherichia coli Using a Broad Host Range Phage Cocktail Targeting Various Bacterial Phylogenetic Groups

Antimicrobial-resistant (AMR) commensal Escherichia coli is a major reservoir that disseminates antimicrobial resistance to humans through the consumption of contaminated foods, such as retail poultry products. This study aimed to control AMR E. coli on retail chicken using a broad host range phage cocktail. Five phages (JEP1, 4, 6, 7, and 8) were isolated and used to construct a phage cocktail after testing infectivity on 67 AMR E. coli strains isolated from retail chicken. Transmission electron microscopic analysis revealed that the five phages belong to the Myoviridae family. The phage genomes had various sizes ranging from 39 to 170 kb and did not possess any genes associated with antimicrobial resistance and virulence. Interestingly, each phage exhibited different levels of infection against AMR E. coli strains depending on the bacterial phylogenetic group. A phage cocktail consisting of the five phages was able to infect AMR E. coli in various phylogenetic groups and inhibited 91.0% (61/67) of AMR E. coli strains used in this study. Furthermore, the phage cocktail was effective in inhibiting E. coli on chicken at refrigeration temperatures. The treatment of artificially contaminated raw chicken skin with the phage cocktail rapidly reduced the viable counts of AMR E. coli by approximately 3 log units within 3 h, and the reduction was maintained throughout the experiment without developing resistance to phage infection. These results suggest that phages can be used as a biocontrol agent to inhibit AMR commensal E. coli on raw chicken.

Tailed Lytic Bacteriophages of Soft Rot Pectobacteriaceae

The study of the ecological and evolutionary traits of Soft Rot Pectobacteriaceae (SRP) comprising genera Pectobacterium and Dickeya often involves bacterial viruses (bacteriophages). Bacteriophages are considered to be a prospective tool for the ecologically safe and highly specific protection of plants and harvests from bacterial diseases. Information concerning bacteriophages has been growing rapidly in recent years, and this has included new genomics-based principles of taxonomic distribution. In this review, we summarise the data on phages infecting Pectobacterium and Dickeya that are available in publications and genomic databases. The analysis highlights not only major genomic properties that assign phages to taxonomic families and genera, but also the features that make them potentially suitable for phage control applications. Specifically, there is a discussion of the molecular mechanisms of receptor recognition by the phages and problems concerning the evolution of phage-resistant mutants.

Characterization of Two New Shiga Toxin-Producing Escherichia coli O103-Infecting Phages Isolated from an Organic Farm

Shiga toxin-producing Escherichia coli (STEC) O103 strains have been recently attributed to various foodborne outbreaks in the United States. Due to the emergence of antibiotic-resistant strains, lytic phages are considered as alternative biocontrol agents. This study was to biologically and genomically characterize two STEC O103-infecting bacteriophages, vB_EcoP-Ro103C3lw (or Ro103C3lw) and vB_EcoM-Pr103Blw (or Pr103Blw), isolated from an organic farm. Based on genomic and morphological analyses, phages Ro103C3lw and Pr103Blw belonged to Autographiviridae and Myoviridae families, respectively. Ro103C3lw contained a 39,389-bp double-stranded DNA and encoded a unique tail fiber with depolymerase activity, resulting in huge plaques. Pr103Blw had an 88,421-bp double-stranded DNA with 26 predicted tRNAs associated with the enhancement of the phage fitness. Within each phage genome, no virulence, antibiotic-resistant, and lysogenic genes were detected. Additionally, Ro103C3lw had a short latent period (2 min) and a narrow host range, infecting only STEC O103 strains. By contrast, Pr103Blw had a large burst size (152 PFU/CFU) and a broad host range against STEC O103, O26, O111, O157:H7, and Salmonella Javiana strains. Furthermore, both phages showed strong antimicrobial activities against STEC O103:H2 strains. The findings provide valuable insight into these two phages’ genomic features with the potential antimicrobial activities against STEC O103.

Isolation and characterization of Hena1 - a novel Erwinia amylovora bacteriophage

Fire blight, caused by plant pathogenic bacterium Erwinia amylovora, is one of the most important diseases of Rosaceae plants. Due to the lack of effective control measures, fire blight infections pose a recurrent threat on agricultural production worldwide. Recently, bacterial viruses, or bacteriophages, have been proposed as environmentally friendly natural antimicrobial agents for fire blight control. Here, we isolated a novel bacteriophage Hena1 with activity against E. amylovora. Further analysis revealed that Hena1 is a narrow-host-range lytic phage belonging to Myoviridae family. Its genome consists of a linear 148,842 bp dsDNA (48.42% GC content) encoding 240 ORFs and 23 tRNA genes. Based on virion structure and genomic composition, Hena1 was classified as a new species of bacteriophage subfamily Vequintavirinae. The comprehensive analysis of Hena1 genome may provide further insights into evolution of bacteriophages infecting plant pathogenic bacteria.

Engineered Bacteriophage Therapeutics: Rationale, Challenges and Future

The current problems with increasing bacterial resistance to antibacterial therapies, resulting in a growing frequency of incurable bacterial infections, necessitates the acceleration of studies on antibacterials of a new generation that could offer an alternative to antibiotics or support their action. Bacteriophages (phages) can kill antibiotic-sensitive as well as antibiotic-resistant bacteria, and thus are a major subject of such studies. Their efficacy in curing bacterial infections has been demonstrated in in vivo experiments and in the clinic. Unlike antibiotics, phages have a narrow range of specificity, which makes them safe for commensal microbiota. However, targeting even only the most clinically relevant strains of pathogenic bacteria requires large collections of well characterized phages, whose specificity would cover all such strains. The environment is a rich source of diverse phages, but due to their complex relationships with bacteria and safety concerns, only some naturally occurring phages can be considered for therapeutic applications. Still, their number and diversity make a detailed characterization of all potentially promising phages virtually impossible. Moreover, no single phage combines all the features required of an ideal therapeutic agent. Additionally, the rapid acquisition of phage resistance by bacteria may make phages already approved for therapy ineffective and turn the search for environmental phages of better efficacy and new specificity into an endless race. An alternative strategy for acquiring phages with desired properties in a short time with minimal cost regarding their acquisition, characterization, and approval for therapy could be based on targeted genome modifications of phage isolates with known properties. The first example demonstrating the potential of this strategy in curing bacterial diseases resistant to traditional therapy is the recent successful treatment of a progressing disseminated Mycobacterium abscessus infection in a teenage patient with the use of an engineered phage. In this review, we briefly present current methods of phage genetic engineering, highlighting their advantages and disadvantages, and provide examples of genetically engineered phages with a modified host range, improved safety or antibacterial activity, and proven therapeutic efficacy. We also summarize novel uses of engineered phages not only for killing pathogenic bacteria, but also for in situ modification of human microbiota to attenuate symptoms of certain bacterial diseases and metabolic, immune, or mental disorders.

A New Pipeline for Designing Phage Cocktails Based on Phage-Bacteria Infection Networks

In recent years, the spread of antibiotic-resistant bacteria and efforts to preserve food microbiota have induced renewed interest in phage therapy. Phage cocktails, instead of a single phage, are commonly used as antibacterial agents since the hosts are unlikely to become resistant to several phages simultaneously. While the spectrum of activity might increase with cocktail complexity, excessive phages could produce side effects, such as the horizontal transfer of genes that augment the fitness of host strains, dysbiosis or high manufacturing costs. Therefore, cocktail formulation represents a compromise between achieving substantial reduction in the bacterial loads and restricting its complexity. Despite the abovementioned points, the observed bacterial load reduction does not increase significantly with the size of phage cocktails, indicating the requirement for a systematic approach to their design. In this work, the information provided by host range matrices was analyzed after building phage-bacteria infection networks (PBINs). To this end, we conducted a meta-analysis of 35 host range matrices, including recently published studies and new datasets comprising Escherichia coli strains isolated during ripening of artisanal raw milk cheese and virulent coliphages from ewes' feces. The nestedness temperature, which reflects the host range hierarchy of the phages, was determined from bipartite host range matrices using heuristic (Nestedness Temperature Calculator) and genetic (BinMatNest) algorithms. The latter optimizes matrix packing, leading to lower temperatures, i.e., it simplifies the identification of the phages with the broadest host range. The structure of infection networks suggests that generalist phages (and not specialist phages) tend to succeed in infecting less susceptible bacteria. A new metric (Φ), which considers some properties of the host range matrices (fill, temperature, and number of bacteria), is proposed as an estimator of phage cocktail size. To identify the best candidates, agglomerative hierarchical clustering using Ward's method was implemented. Finally, a cocktail was formulated for the biocontrol of cheese-isolated E. coli, reducing bacterial counts by five orders of magnitude.

Targeting of Mammalian Glycans Enhances Phage Predation in the Gastrointestinal Tract

The human gastrointestinal mucosal surface consists of a eukaryotic epithelium, a prokaryotic microbiota, and a carbohydrate-rich interface that separates them. In the gastrointestinal tract, the interaction of bacteriophages (phages) and their prokaryotic hosts influences the health of the mammalian host, especially colonization with invasive pathobionts. Antibiotics may be used, but they also kill protective commensals. Here, we report a novel phage whose lytic cycle is enhanced in intestinal environments. The tail fiber gene, whose protein product binds human heparan sulfated proteoglycans and localizes the phage to the epithelial cell surface, positions it near its bacterial host, a type of locational targeting mechanism. This finding offers the prospect of developing mucosal targeting phage to selectively remove invasive pathobiont species from mucosal surfaces.IMPORTANCE Invasive pathobionts or microbes capable of causing disease can reside deep within the mucosal epithelium of our gastrointestinal tract. Targeted effective antibacterial therapies are needed to combat these disease-causing organisms, many of which may be multidrug resistant. Here, we isolated a lytic bacteriophage (phage) that can localize to the epithelial surface by binding heparan sulfated glycans, positioning it near its host, Escherichia coli This targeted therapy can be used to selectively remove invasive pathobionts from the gastrointestinal tract, preventing the development of disease.

Compilation of Escherichia coli K-12 outer membrane phage receptors - their function and some historical remarks

Many Escherichia coli phages have been sequenced, but in most cases their sequences alone do not suffice to predict their host specificity. Analysis of phage resistant E. coli K-12 mutants have uncovered a certain set of outer membrane proteins and polysaccharides as receptors. In this review, a compilation of E. coli K12 phage receptors is provided and their functional characterization, often driven by studies on phage resistant mutants, is discussed in the historical context. While great progress has been made in this field thus far, several proteins in the outer membrane still await characterization as phage receptors.

Characterization of Endolysin LysECP26 Derived from rV5-like Phage vB_EcoM-ECP26 for Inactivation of Escherichia coli O157:H7

With an increase in the consumption of non-heated fresh food, foodborne shiga toxin-producing Escherichia coli (STEC) has emerged as one of the most problematic pathogens worldwide. Endolysin, a bacteriophage-derived lysis protein, is able to lyse the target bacteria without any special resistance, and thus has been garnering interest as a powerful antimicrobial agent. In this study, rV5-like phage endolysin targeting E. coli O157:H7, named as LysECP26, was identified and purified. This endolysin had a lysozyme-like catalytic domain, but differed markedly from the sequence of lambda phage endolysin. LysECP26 exhibited strong activity with a broad lytic spectrum against various gram-negative strains (29/29) and was relatively stable at a broad temperature range (4°C- 55°C). The optimum temperature and pH ranges of LysECP26 were identified at 37°C-42°C and pH 7- 8, respectively. NaCl supplementation did not affect the lytic activity. Although LysECP26 was limited in that it could not pass the outer membrane, E. coli O157: H7 could be effectively controlled by adding ethylenediaminetetraacetic acid (EDTA) and citric acid (1.44 and 1.14 log CFU/ml) within 30 min. Therefore, LysECP26 may serv as an effective biocontrol agent for gram-negative pathogens, including E. coli O157:H7.

Multisubunit RNA Polymerases of Jumbo Bacteriophages

Prokaryotic viruses with DNA genome longer than 200 kb are collectively referred to as “jumbo phages”. Some representatives of this phylogenetically diverse group encode two DNA-dependent RNA polymerases (RNAPs)—a virion RNAP and a non-virion RNAP. In contrast to most other phage-encoded RNAPs, the jumbo phage RNAPs are multisubunit enzymes related to RNAPs of cellular organisms. Unlike all previously characterized multisubunit enzymes, jumbo phage RNAPs lack the universally conserved alpha subunits required for enzyme assembly. The mechanism of promoter recognition is also different from those used by cellular enzymes. For example, the AR9 phage non-virion RNAP requires uracils in its promoter and is able to initiate promoter-specific transcription from single-stranded DNA. Jumbo phages encoding multisubunit RNAPs likely have a common ancestor allowing making them a separate subgroup within the very diverse group of jumbo phages. In this review, we describe transcriptional strategies used by RNAP-encoding jumbo phages and describe the properties of characterized jumbo phage RNAPs.

New insights into the biodiversity of coliphages in the intestine of poultry

Despite phages' ubiquitous presence and great importance in shaping microbial communities, little is known about the diversity of specific phages in different ecological niches. Here, we isolated, sequenced, and characterized 38 Escherichia coli-infecting phages (coliphages) from poultry faeces to gain a better understanding of the coliphage diversity in the poultry intestine. All phages belonged to either the Siphoviridae or Myoviridae family and their genomes ranged between 44,324 and 173,384 bp, with a G+C content between 35.5 and 46.4%. Phylogenetic analysis was performed based on single "marker" genes; the terminase large subunit, portal protein, and exonucleases, as well as the full draft genomes. Single gene analysis resulted in six distinct clusters. Only minor differences were observed between the different phylogenetic analyses, including branch lengths and additional duplicate or triplicate subclustering. Cluster formation was according to genome size, G+C content and phage subfamily. Phylogenetic analysis based on the full genomes supported these clusters. Moreover, several of our Siphoviridae phages might represent a novel unclassified phage genus. This study allowed for identification of several novel coliphages and provides new insights to the coliphage diversity in the intestine of poultry. Great diversity was observed amongst the phages, while they were isolated from an otherwise similar ecosystem.

Shining Light on Human Gut Bacteriophages

The human gut is a complex environment that contains a multitude of microorganisms that are collectively termed the microbiome. Multiple factors have a role to play in driving the composition of human gut bacterial communities either toward homeostasis or the instability that is associated with many disease states. One of the most important forces are likely to be bacteriophages, bacteria-infecting viruses that constitute by far the largest portion of the human gut virome. Despite this, bacteriophages (phages) are the one of the least studied residents of the gut. This is largely due to the challenges associated with studying these difficult to culture entities. Modern high throughput sequencing technologies have played an important role in improving our understanding of the human gut phageome but much of the generated sequencing data remains uncharacterised. Overcoming this requires database-independent bioinformatic pipelines and even those phages that are successfully characterized only provide limited insight into their associated biological properties, and thus most viral sequences have been characterized as “viral dark matter.” Fundamental to understanding the role of phages in shaping the human gut microbiome, and in turn perhaps influencing human health, is how they interact with their bacterial hosts. An essential aspect is the isolation of novel phage-bacteria host pairs by direct isolation through various screening methods, which can transform in silico phages into a biological reality. However, this is also beset with multiple challenges including culturing difficulties and the use of traditional methods, such as plaquing, which may bias which phage-host pairs that can be successfully isolated. Phage-bacteria interactions may be influenced by many aspects of complex human gut biology which can be difficult to reproduce under laboratory conditions. Here we discuss some of the main findings associated with the human gut phageome to date including composition, our understanding of phage-host interactions, particularly the observed persistence of virulent phages and their hosts, as well as factors that may influence these highly intricate relationships. We also discuss current methodologies and bottlenecks hindering progression in this field and identify potential steps that may be useful in overcoming these hurdles.

Exploring the Remarkable Diversity of Culturable Escherichia coli Phages in the Danish Wastewater Environment

Phages drive bacterial diversity, profoundly influencing microbial communities, from microbiomes to the drivers of global biogeochemical cycling. Aiming to broaden our understanding of Escherichiacoli (MG1655, K-12) phages, we screened 188 Danish wastewater samples and isolated 136 phages. Ninety-two of these have genomic sequences with less than 95% similarity to known phages, while most map to existing genera several represent novel lineages. The isolated phages are highly diverse, estimated to represent roughly one-third of the true diversity of culturable virulent dsDNA Escherichia phages in Danish wastewater, yet almost half (40%) are not represented in metagenomic databases, emphasising the importance of isolating phages to uncover diversity. Seven viral families, Myoviridae, Siphoviridae, Podoviridae,Drexlerviridae,Chaseviridae,Autographviridae, and Microviridae, are represented in the dataset. Their genomes vary drastically in length from 5.3 kb to 170.8 kb, with a guanine and cytosine (GC) content ranging from 35.3% to 60.0%. Hence, even for a model host bacterium, substantial diversity remains to be uncovered. These results expand and underline the range of coliphage diversity and demonstrate how far we are from fully disclosing phage diversity and ecology.

Paving the Way to Unveil the Diversity and Evolution of Phage Genomes

Phage biology has been developing for the last hundred years, and the potential of phages as tools and treatments has been known since their early discovery. However, the lack of knowledge of the molecular mechanisms coded in phage genomes hindered the development of the field. With current molecular methods, the last decade has been a resurgence of the field. The Special Issue on “Diversity and Evolution of Phage Genomes” is a great example with its 17 manuscripts published. It covers some of the latest methods to sample and characterize environmental and host associated viromes, considering experimental biases and computational developments. Furthermore, the use of molecular tools coupled with traditional methods has allowed to isolate and characterize viruses from different hosts and environments with such diversity that even a new viral class is being proposed. The viruses described cover all different phage families and lifestyles. However, is not only about diversity; the molecular evolution is studied in a set of manuscripts looking at phage-host interactions and their capacity to uncover the frequency and type of mutations behind the bacterial resistance mechanisms and viral pathogenesis, and such methods are opening new ways into identifying potential receptors and characterizing the bacterial host range.