Discovery of an expansive bacteriophage family that includes the most abundant viruses from the human gut

Longitudinal analysis of the enteric virome in paediatric subjects from the Free State Province, South Africa, reveals early gut colonisation and temporal dynamics

The gut of healthy neonates is devoid of viruses at birth, but rapidly becomes colonised by normal viral commensals that aid in important physiological functions like metabolism but can, in some instances, result in gastrointestinal illnesses. However, little is known about how this colonisation begins, its variability and factors shaping the gut virome composition. Thus, understanding the development, assembly, and progression of enteric viral communities over time is key. To explore early-life virome development, metagenomic sequencing was employed in faecal samples collected longitudinally from a cohort of 17 infants during their first six months of life. The gut virome analysis revealed a diverse and dynamic viral community, formed by a richness of different viruses infecting humans, non-human mammals, bacteria, and plants. Eukaryotic viruses were detected as early as one week of life, increasing in abundance and diversity over time. Most of the viruses detected are commonly associated with gastroenteritis and include members of the Caliciviridae, Picornaviridae, Astroviridae, Adenoviridae, and Sedoreoviridae families. The most common co-occurrences involved asymptomatic norovirus-parechovirus, norovirus-sapovirus, sapovirus-parechovirus, observed in at least 40 % of the samples. Majority of the plant-derived viruses detected in the infants' gut were from the Virgaviridae family. This study demonstrates the first longitudinal characterisation of the gastrointestinal virome in infants, from birth up to 6 months of age, in sub-Saharan Africa. Overall, the findings from this study delineate the composition and variability of the healthy infants' gut virome over time, which is a significant step towards understanding the dynamics and biogeography of viral communities in the infant gut.

CrAss-Like Phages: From Discovery in Human Fecal Metagenome to Application as a Microbial Source Tracking Marker

CrAss-like phages are a diverse group of bacteriophages genetically similar to the prototypical crAssphage (p-crAssphage), which was discovered in the human gut microbiome through a metagenomics approach. It was identified as a ubiquitous and highly abundant bacteriophage group in the gut microbiome. Initial co-occurrence analysis postulated Bacteroides spp. as the prospective bacterial host. Subsequent studies have confirmed multiple host species under Phylum Bacteroidetes and some Firmicutes. Detection of crAss-like phages in sewage-contaminated environmental water and robust correlation with enteric viruses and bacteria has culminated in their adoption as a microbial source tracking (MST) marker. Polymerase chain reaction (PCR) and real-time PCR assays have been developed utilizing the conserved genes in the p-crAssphage genome to detect human fecal contamination of different water sources, with high specificity. Numerous investigations have examined the implications of crAss-like phages in diverse disease conditions, including ulcerative colitis, obesity and metabolic syndrome, autism spectrum disorders, rheumatoid arthritis, atopic eczema, and other autoimmune disorders. These studies have unveiled associations between certain diseases and diminished abundance and diversity of crAss-like phages. This review offers insights into the diverse aspects of research on crAss-like phages, including their discovery, genomic characteristics, structure, taxonomy, isolation, molecular detection, application as an MST marker, and role as a gut microbiome modulator with consequential health implications.

Assessing phage-host population dynamics by reintroducing virulent viruses to synthetic microbiomes

Microbiomes feature complex interactions between diverse bacteria and bacteriophages. Synthetic microbiomes offer a powerful way to study these interactions; however, a major challenge is obtaining a representative bacteriophage population during the bacterial isolation process. We demonstrate that colony isolation reliably excludes virulent viruses from sample sources with low virion-to-bacteria ratios such as feces, creating "virulent virus-free" controls. When the virulent dsDNA virome is reintroduced to a 73-strain synthetic gut microbiome in a bioreactor model of the human colon, virulent viruses target susceptible strains without significantly altering community structure or metabolism. In addition, we detected signals of prophage induction that associate with virulent predation. Overall, our findings indicate that dilution-based isolation methods generate synthetic gut microbiomes that are heavily depleted, if not devoid, of virulent viruses and that such viruses, if reintroduced, have a targeted effect on community assembly, metabolism, and prophage replication.

Another piece of the puzzle for the human microbiome: the gut virome under dietary modulation

The virome is the most abundant and highly variable microbial consortium in the gut. Because of difficulties in isolating and culturing gut viruses and consequently shorting of reference genomes, the virome has remained a relatively elusive aspect of the human microbiome. In recent years, studies on the virome have accumulated growing evidence showing that the virome is diet-modulated and widely involved in regulating health. Here, we review the responses of the gut virome to dietary intake and the potential health implications, presenting changes in the gut viral community, preferences of viral members to particular diets. We further discuss how viral-bacterial interactions and phage lifestyle shifts shape the gut microbiota. We also discuss the specific functions conferred by diet on the gut virome and bacterial community in the context of horizontal gene transfer, as well as the import of new viral members along with the diet. Collating these studies will expand our understanding of the dietary regulation of the gut virome and inspire dietary interventions and health maintenance strategies targeting the gut microbiota.

The Potential of Co-Evolution and Interactions of Gut Bacteria-Phages in Bamboo-Eating Pandas: Insights from Dietary Preference-Based Metagenomic Analysis

Bacteria and phages are two of the most abundant biological entities in the gut microbiome, and diet and host phylogeny are two of the most critical factors influencing the gut microbiome. A stable gut bacterial community plays a pivotal role in the host's physiological development and immune health. A phage is a virus that directly infects bacteria, and phages' close associations and interactions with bacteria are essential for maintaining the stability of the gut bacterial community and the entire microbial ecosystem. Here, we utilized 99 published metagenomic datasets from 38 mammalian species to investigate the relationship (diversity and composition) and potential interactions between gut bacterial and phage communities and the impact of diet and phylogeny on these communities. Our results highlight the co-evolutionary potential of bacterial-phage interactions within the mammalian gut. We observed a higher alpha diversity in gut bacteria than in phages and identified positive correlations between bacterial and phage compositions. Furthermore, our study revealed the significant influence of diet and phylogeny on mammalian gut bacterial and phage communities. We discovered that the impact of dietary factors on these communities was more pronounced than that of phylogenetic factors at the order level. In contrast, phylogenetic characteristics had a more substantial influence at the family level. The similar omnivorous dietary preference and closer phylogenetic relationship (family Ursidae) may contribute to the similarity of gut bacterial and phage communities between captive giant panda populations (GPCD and GPYA) and omnivorous animals (OC; including Sun bear, brown bear, and Asian black bear). This study employed co-occurrence microbial network analysis to reveal the potential interaction patterns between bacteria and phages. Compared to other mammalian groups (carnivores, herbivores, and omnivores), the gut bacterial and phage communities of bamboo-eating species (giant pandas and red pandas) exhibited a higher level of interaction. Additionally, keystone species and modular analysis showed the potential role of phages in driving and maintaining the interaction patterns between bacteria and phages in captive giant pandas. In sum, gaining a comprehensive understanding of the interaction between the gut microbiota and phages in mammals is of great significance, which is of great value in promoting healthy and sustainable mammals and may provide valuable insights into the conservation of wildlife populations, especially endangered animal species.

Genome Analysis of Epsilon CrAss-like Phages

CrAss-like phages play an important role in maintaining ecological balance in the human intestinal microbiome. However, their genetic diversity and lifestyle are still insufficiently studied. In this study, a novel CrAssE-Sib phage genome belonging to the epsilon crAss-like phage genomes was found. Comparative analysis indicated that epsilon crAss-like phages are divided into two putative genera, which were proposed to be named Epsilonunovirus and Epsilonduovirus; CrAssE-Sib belongs to the former. The crAssE-Sib genome contains a diversity-generating retroelement (DGR) cassette with all essential elements, including the reverse transcriptase (RT) and receptor binding protein (RBP) genes. However, this RT contains the GxxxSP motif in its fourth domain instead of the usual GxxxSQ motif found in all known phage and bacterial DGRs. RBP encoded by CrAssE-Sib and other Epsilonunoviruses has an unusual structure, and no similar phage proteins were found. In addition, crAssE-Sib and other Epsilonunoviruses encode conserved prophage repressor and anti-repressors that could be involved in lysogenic-to-lytic cycle switches. Notably, DNA primase sequences of epsilon crAss-like phages are not included in the monophyletic group formed by the DNA primases of all other crAss-like phages. Therefore, epsilon crAss-like phage substantially differ from other crAss-like phages, indicating the need to classify these phages into a separate family.

Analysis and culturing of the prototypic crAssphage reveals a phage-plasmid lifestyle

The prototypic crAssphage (Carjivirus communis) is one of the most abundant, prevalent, and persistent gut bacteriophages, yet it remains uncultured and its lifestyle uncharacterized. For the last decade, crAssphage has escaped plaque-dependent culturing efforts, leading us to investigate alternative lifestyles that might explain its widespread success. Through genomic analyses and culturing, we find that crAssphage uses a phage-plasmid lifestyle to persist extrachromosomally. Plasmid-related genes are more highly expressed than those implicated in phage maintenance. Leveraging this finding, we use a plaque-free culturing approach to measure crAssphage replication in culture with Phocaeicola vulgatus, Phocaeicola dorei, and Bacteroides stercoris, revealing a broad host range. We demonstrate that crAssphage persists with its hosts in culture without causing major cell lysis events or integrating into host chromosomes. The ability to switch between phage and plasmid lifestyles within a wide range of hosts contributes to the prolific nature of crAssphage in the human gut microbiome.

Wastewater-based surveillance as a tool for public health action: SARS-CoV-2 and beyond

Wastewater-based surveillance (WBS) has undergone dramatic advancement in the context of the coronavirus disease 2019 (COVID-19) pandemic. The power and potential of this platform technology were rapidly realized when it became evident that not only did WBS-measured SARS-CoV-2 RNA correlate strongly with COVID-19 clinical disease within monitored populations but also, in fact, it functioned as a leading indicator. Teams from across the globe rapidly innovated novel approaches by which wastewater could be collected from diverse sewersheds ranging from wastewater treatment plants (enabling community-level surveillance) to more granular locations including individual neighborhoods and high-risk buildings such as long-term care facilities (LTCF). Efficient processes enabled SARS-CoV-2 RNA extraction and concentration from the highly dilute wastewater matrix. Molecular and genomic tools to identify, quantify, and characterize SARS-CoV-2 and its various variants were adapted from clinical programs and applied to these mixed environmental systems. Novel data-sharing tools allowed this information to be mobilized and made immediately available to public health and government decision-makers and even the public, enabling evidence-informed decision-making based on local disease dynamics. WBS has since been recognized as a tool of transformative potential, providing near-real-time cost-effective, objective, comprehensive, and inclusive data on the changing prevalence of measured analytes across space and time in populations. However, as a consequence of rapid innovation from hundreds of teams simultaneously, tremendous heterogeneity currently exists in the SARS-CoV-2 WBS literature. This manuscript provides a state-of-the-art review of WBS as established with SARS-CoV-2 and details the current work underway expanding its scope to other infectious disease targets.

A cryptic plasmid is among the most numerous genetic elements in the human gut

Plasmids are extrachromosomal genetic elements that often encode fitness-enhancing features. However, many bacteria carry "cryptic" plasmids that do not confer clear beneficial functions. We identified one such cryptic plasmid, pBI143, which is ubiquitous across industrialized gut microbiomes and is 14 times as numerous as crAssphage, currently established as the most abundant extrachromosomal genetic element in the human gut. The majority of mutations in pBI143 accumulate in specific positions across thousands of metagenomes, indicating strong purifying selection. pBI143 is monoclonal in most individuals, likely due to the priority effect of the version first acquired, often from one's mother. pBI143 can transfer between Bacteroidales, and although it does not appear to impact bacterial host fitness in vivo, it can transiently acquire additional genetic content. We identified important practical applications of pBI143, including its use in identifying human fecal contamination and its potential as an alternative approach to track human colonic inflammatory states.

Exploring the gut DNA virome in fecal immunochemical test stool samples reveals associations with lifestyle in a large population-based study

Stool samples for fecal immunochemical tests (FIT) are collected in large numbers worldwide as part of colorectal cancer screening programs. Employing FIT samples from 1034 CRCbiome participants, recruited from a Norwegian colorectal cancer screening study, we identify, annotate and characterize more than 18000 DNA viruses, using shotgun metagenome sequencing. Only six percent of them are assigned to a known taxonomic family, with Microviridae being the most prevalent viral family. Linking individual profiles to comprehensive lifestyle and demographic data shows 17/25 of the variables to be associated with the gut virome. Physical activity, smoking, and dietary fiber consumption exhibit strong and consistent associations with both diversity and relative abundance of individual viruses, as well as with enrichment for auxiliary metabolic genes. We demonstrate the suitability of FIT samples for virome analysis, opening an opportunity for large-scale studies of this enigmatic part of the gut microbiome. The diverse viral populations and their connections to the individual lifestyle uncovered herein paves the way for further exploration of the role of the gut virome in health and disease.

Assessment of crAssphage as a human fecal source tracking marker in the lower Great Lakes

CrAssphage or crAss-like phage ranks as the most abundant phage in the human gut and is present in human feces-contaminated environments. Due to its high human specificity and sensitivity, crAssphage is a potentially robust source tracking indicator that can distinguish human fecal contamination from agricultural or wildlife sources. Its suitability in the Great Lakes area, one of the world's most important water systems, has not been well tested. In this study, we tested a qPCR-based quantification method using two crAssphage marker genes (ORF18-mod and CPQ_064) at Toronto recreational beaches along with their adjacent river mouths. Our results showed a 71.4 % (CPQ_064) and 100 % (ORF18-mod) human sensitivity for CPQ_064 and ORF18-mod, and a 100 % human specificity for both marker genes. CrAssphage was present in 57.7 % or 71.2 % of environmental water samples, with concentrations ranging from 1.45 to 5.14 log10 gene copies per 100 mL water. Though concentrations of the two marker genes were strongly correlated, ORF18-mod features a higher human sensitivity and higher positive detection rates in environmental samples. Quantifiable crAssphage was mostly present in samples collected in June and July 2021 associated with higher rainfall. In addition, rivers had more frequent crAssphage presence and higher concentrations than their associated beaches, indicating more frequent and greater human fecal contamination in the rivers. However, crAssphage was more correlated with E. coli and Enterococcus at the beaches than in the rivers, suggesting human fecal sources may be more predominant in driving the increases in E. coli and Enterococcus at the beaches when impacted by river plumes.

Megataxonomy and global ecology of the virosphere

Nearly all organisms are hosts to multiple viruses that collectively appear to be the most abundant biological entities in the biosphere. With recent advances in metagenomics and metatranscriptomics, the known diversity of viruses substantially expanded. Comparative analysis of these viruses using advanced computational methods culminated in the reconstruction of the evolution of major groups of viruses and enabled the construction of a virus megataxonomy, which has been formally adopted by the International Committee on Taxonomy of Viruses. This comprehensive taxonomy consists of six virus realms, which are aspired to be monophyletic and assembled based on the conservation of hallmark proteins involved in capsid structure formation or genome replication. The viruses in different major taxa substantially differ in host range and accordingly in ecological niches. In this review article, we outline the latest developments in virus megataxonomy and the recent discoveries that will likely lead to reassessment of some major taxa, in particular, split of three of the current six realms into two or more independent realms. We then discuss the correspondence between virus taxonomy and the distribution of viruses among hosts and ecological niches, as well as the abundance of viruses versus cells in different habitats. The distribution of viruses across environments appears to be primarily determined by the host ranges, i.e. the virome is shaped by the composition of the biome in a given habitat, which itself is affected by abiotic factors.

Tail-tape-fused virion and non-virion RNA polymerases of a thermophilic virus with an extremely long tail

Thermus thermophilus bacteriophage P23-45 encodes a giant 5,002-residue tail tape measure protein (TMP) that defines the length of its extraordinarily long tail. Here, we show that the N-terminal portion of P23-45 TMP is an unusual RNA polymerase (RNAP) homologous to cellular RNAPs. The TMP-fused virion RNAP transcribes pre-early phage genes, including a gene that encodes another, non-virion RNAP, that transcribes early and some middle phage genes. We report the crystal structures of both P23-45 RNAPs. The non-virion RNAP has a crab-claw-like architecture. By contrast, the virion RNAP adopts a unique flat structure without a clamp. Structure and sequence comparisons of the P23-45 RNAPs with other RNAPs suggest that, despite the extensive functional differences, the two P23-45 RNAPs originate from an ancient gene duplication in an ancestral phage. Our findings demonstrate striking adaptability of RNAPs that can be attained within a single virus species.

Microbial transmission in the social microbiome and host health and disease

Although social interactions are known to drive pathogen transmission, the contributions of socially transmissible host-associated mutualists and commensals to host health and disease remain poorly explored. We use the concept of the social microbiome-the microbial metacommunity of a social network of hosts-to analyze the implications of social microbial transmission for host health and disease. We investigate the contributions of socially transmissible microbes to both eco-evolutionary microbiome community processes (colonization resistance, the evolution of virulence, and reactions to ecological disturbance) and microbial transmission-based processes (transmission of microbes with metabolic and immune effects, inter-specific transmission, transmission of antibiotic-resistant microbes, and transmission of viruses). We consider the implications of social microbial transmission for communicable and non-communicable diseases and evaluate the importance of a socially transmissible component underlying canonically non-communicable diseases. The social transmission of mutualists and commensals may play a significant, under-appreciated role in the social determinants of health and may act as a hidden force in social evolution.

Role of the immune system in liver transplantation and its implications for therapeutic interventions

Liver transplantation (LT) stands as the gold standard for treating end-stage liver disease and hepatocellular carcinoma, yet postoperative complications continue to impact survival rates. The liver's unique immune system, governed by a microenvironment of diverse immune cells, is disrupted during processes like ischemia-reperfusion injury posttransplantation, leading to immune imbalance, inflammation, and subsequent complications. In the posttransplantation period, immune cells within the liver collaboratively foster a tolerant environment, crucial for immune tolerance and liver regeneration. While clinical trials exploring cell therapy for LT complications exist, a comprehensive summary is lacking. This review provides an insight into the intricacies of the liver's immune microenvironment, with a specific focus on macrophages and T cells as primary immune players. Delving into the immunological dynamics at different stages of LT, we explore the disruptions after LT and subsequent immune responses. Focusing on immune cell targeting for treating liver transplant complications, we provide a comprehensive summary of ongoing clinical trials in this domain, especially cell therapies. Furthermore, we offer innovative treatment strategies that leverage the opportunities and prospects identified in the therapeutic landscape. This review seeks to advance our understanding of LT immunology and steer the development of precise therapies for postoperative complications.

Genomes of a Novel Group of Phages That Use Alternative Genetic Code Found in Human Gut Viromes

Metagenomics provides detection of phage genome sequences in various microbial communities. However, the use of alternative genetic codes by some phages precludes the correct analysis of their genomes. In this study, the unusual phage genome (phAss-1, 135,976 bp) was found after the de novo assembly of the human gut virome. Genome analysis revealed the presence of the TAG stop codons in 41 ORFs, including characteristic phage ORFs, and three genes of suppressor tRNA. Comparative analysis indicated that no phages with similar genomes were described. However, two phage genomes (BK046881_ctckW2 and BK025033_ct6IQ4) with substantial similarity to phAss-1 were extracted from the human gut metagenome data. These two complete genomes demonstrated 82.7% and 86.4% of nucleotide identity, respectively, similar genome synteny to phAss-1, the presence of suppressor tRNA genes and suppressor TAG stop codons in many characteristic phage ORFs. These data indicated that phAss-1, BK046881_ctckW2, and BK025033_ct6IQ4 are distinct species within the proposed Phassvirus genus. Moreover, a monophyletic group of divergent phage genomes containing the proposed Phassvirus genus was found among metagenome data. Several phage genomes from the group also contain ORFs with suppressor TAG stop codons, indicating the need to use various translation tables when depositing phage genomes in GenBank.

Asymmetric Structure of Podophage GP4 Reveals a Novel Architecture of Three Types of Tail Fibers

Bacteriophage tail fibers (or called tail spikes) play a critical role in the early stage of infection by binding to the bacterial surface. Podophages with known structures usually possess one or two types of fibers. Here, we resolved an asymmetric structure of the podophage GP4 to near-atomic resolution by cryo-EM. Our structure revealed a symmetry-mismatch relationship between the components of the GP4 tail with previously unseen topologies. In detail, two dodecameric adaptors (adaptors I and II), a hexameric nozzle, and a tail needle form a conserved tail body connected to a dodecameric portal occupying a unique vertex of the icosahedral head. However, five chain-like extended fibers (fiber I) and five tulip-like short fibers (fiber II) are anchored to a 15-fold symmetric fiber-tail adaptor, encircling the adaptor I, and six bamboo-like trimeric fibers (fiber III) are connected to the nozzle. Five fibers I, each composed of five dimers of the protein gp80 linked by an elongated rope protein, are attached to the five edges of the tail vertex of the icosahedral head. In this study, we identified a new structure of the podophage with three types of tail fibers, and such phages with different types of fibers may have a broad host range and/or infect host cells with considerably high efficiency, providing evolutionary advantages in harsh environments.

Impact of gut microbiota on liver transplantation

The gut microbiota has been gaining attention due to its interactions with the human body and its role in pathophysiological processes. One of the main interactions is the "gut-liver axis," in which disruption of the gut mucosal barrier seen in portal hypertension and liver disease can influence liver allograft function over time. For example, in patients who are undergoing liver transplantation, preexisting dysbiosis, perioperative antibiotic use, surgical stress, and immunosuppressive use have each been associated with alterations in gut microbiota, potentially impacting overall morbidity and mortality. In this review, studies exploring gut microbiota changes in patients undergoing liver transplantation are reviewed, including both human and experimental animal studies. Common themes include an increase in Enterobacteriaceae and Enterococcaceae species and a decrease in Faecalibacterium prausnitzii and Bacteriodes, while a decrease in the overall diversity of gut microbiota after liver transplantation.

Factors Affecting Variation of the Human Gut Phageome

The gut microbiome is a dense and metabolically active consortium of microorganisms and viruses located in the lower gastrointestinal tract of the human body. Bacteria and their viruses (phages) are the most abundant members of the gut microbiome. Investigating their biology and the interplay between the two is important if we are to understand their roles in human health and disease. In this review, we summarize recent advances in resolving the taxonomic structure and ecological functions of the complex community of phages in the human gut-the gut phageome. We discuss how age, diet, and geography can all have a significant impact on phageome composition. We note that alterations to the gut phageome have been observed in several diseases such as inflammatory bowel disease, irritable bowel syndrome, and colorectal cancer, and we evaluate whether these phageome changes can directly or indirectly contribute to disease etiology and pathogenesis. We also highlight how lack of standardization in studying the gut phageome has contributed to variation in reported results.

Prevalence and Genetic Diversity of Cross-Assembly Phages in Wastewater Treatment Plants in Riyadh, Saudi Arabia

The most common DNA virus found in wastewaters globally is the cross-assembly phage (crAssphage). King Saud University wastewater treatment plant (KSU-WWTP); Manfoha wastewater treatment plant (MN-WWTP); and the Embassy wastewater treatment plant (EMB-WWTP) in Riyadh, Saudi Arabia were selected, and 36 untreated sewage water samples during the year 2022 were used in the current study. The meteorological impact on crAssphage prevalence was investigated. CrAssphage prevalence was recorded using PCR and Sanger sequencing. The molecular diversity of crAssphage sequences was studied for viral gene segments from the major capsid protein (MCP) and membrane protein containing the peptidoglycan-binding domain (MP-PBD). KSU-WWTP and EMB-WWTP showed a higher prevalence of crAssphage (83.3%) than MN-WWTP (75%). Phylogenetic analysis of MCP and MP-PBD segments depicted a close relationship to the Japanese isolates. The MCP gene from the current study's isolate WW/2M/SA/2022 depicted zero evolutionary divergence from 3057_98020, 2683_104905, and 4238_99953 isolates (d = 0.000) from Japan. A significant influence of temporal variations on the prevalence of crAssphage was detected in the three WWTPs. CrAssphage displayed the highest prevalence at high temperatures (33-44 °C), low relative humidity (6-14%), and moderate wind speed (16-21 Km/h). The findings provided pioneering insights into crAssphage prevalence and its genetic diversity in WWTPs in Riyadh, Saudi Arabia.

Prophage identification and molecular analysis in the genomes of Pseudomonas aeruginosa strains isolated from critical care patients

Prophages are bacteriophages integrated into the bacterial host's chromosome. This research aims to analyze and characterize the existing prophages within a collection of 53 Pseudomonas aeruginosa strains from intensive care units (ICUs) in Portugal and Spain. A total of 113 prophages were localized in the collection, with 18 of them being present in more than one strain simultaneously. After annotation, five of them were discarded as incomplete, and the 13 remaining prophages were characterized. Of 13, 10 belonged to the siphovirus tail morphology group, 2 to the podovirus tail morphology group, and 1 to the myovirus tail morphology group. All prophages had a length ranging from 20,199 to 63,401 bp and a GC% between 56.2% and 63.6%. The number of open reading frames (ORFs) oscillated between 32 and 88, and in 3/13 prophages, more than 50% of the ORFs had an unknown function. With our findings, we show that prophages are present in the majority of the P. aeruginosa strains isolated from Portuguese and Spanish critically ill patients, many of them found in more than one circulating strain at the same time and following a similar clonal distribution pattern. Although a great sum of ORFs had an unknown function, number of proteins in relation to viral defense (anti-CRISPR proteins, toxin/antitoxin modules, proteins against restriction-modification systems) as well as to prophage interference into their host's quorum sensing system and regulatory cascades were found. This supports the idea that prophages have an influence in bacterial pathogenesis and anti-phage defense. IMPORTANCE Despite being known for decades, prophages remain understudied when compared to the lytic phages employed in phage therapy. This research aims to shed some light into the nature, composition, and role of prophages found within a set of circulating strains of Pseudomas aeruginosa, with special attention to high-risk clones. Given the fact that prophages can effectively influence bacterial pathogenesis, prophage basic research constitutes a topic of growing interest. Furthermore, the abundance of viral defense and regulatory proteins within prophage genomes detected in this study evidences the importance of characterizing the most frequent prophages in circulating clinical strains and in high-risk clones if phage therapy is to be used.

Characterization of crAss-like phage isolates highlights Crassvirales genetic heterogeneity and worldwide distribution

Crassvirales (crAss-like phages) are an abundant group of human gut-specific bacteriophages discovered in silico. The use of crAss-like phages as human fecal indicators is proposed but the isolation of only seven cultured strains of crAss-like phages to date has greatly hindered their study. Here, we report the isolation and genetic characterization of 25 new crAss-like phages (termed crAssBcn) infecting Bacteroides intestinalis, belonging to the order Crassvirales, genus Kehishuvirus and, based on their genomic variability, classified into six species. CrAssBcn phage genomes are similar to ΦCrAss001 but show genomic and aminoacidic differences when compared to other crAss-like phages of the same family. CrAssBcn phages are detected in fecal metagenomes around the world at a higher frequency than ΦCrAss001. This study increases the known crAss-like phage isolates and their abundance and heterogeneity open the question of what member of the Crassvirales group should be selected as human fecal marker.

MgCod: Gene Prediction in Phage Genomes with Multiple Genetic Codes

Massive sequencing of microbiomes has led to the discovery of a large number of phage genomes with intermittent stop codon recoding. We have developed a computational tool, MgCod, that identifies genomic regions (blocks) with distinct stop codon recoding simultaneously with the prediction of protein-coding regions. When MgCod was used to scan a large volume of human metagenomic contigs hundreds of viral contigs with intermittent stop codon recoding were revealed. Many of these contigs originated from genomes of known crAssphages. Further analyses had shown that intermittent recoding was associated with subtle patterns in the organization of protein-coding genes, such as 'single-coding' and 'dual-coding'. The dual-coding genes, clustered into blocks, could be translated by two alternative codes producing nearly identical proteins. It was observed that the dual-coded blocks were enriched with the early-stage phage genes, while the late-stage genes were residing in the single-coded blocks. MgCod can identify types of stop codon recoding in novel genomic sequences in parallel with gene prediction. It is available for download from https://github.com/gatech-genemark/MgCod.

The human gut phageome: composition, development, and alterations in disease

The human gastrointestinal tract is colonized by a large number of microorganisms, including bacteria, archaea, viruses, and eukaryotes. The bacterial community has been widely confirmed to have a significant impact on human health, while viruses, particularly phages, have received less attention. Phages are viruses that specifically infect bacteria. They are abundant in the biosphere and exist in a symbiotic relationship with their host bacteria. Although the application of high-throughput sequencing and bioinformatics technology has greatly improved our understanding of the genomic diversity, taxonomic composition, and spatio-temporal dynamics of the human gut phageome, there is still a large portion of sequencing data that is uncharacterized. Preliminary studies have predicted that the phages play a crucial role in driving microbial ecology and evolution. Prior to exploring the function of phages, it is necessary to address the obstacles that hinder establishing a comprehensive sequencing database with sufficient biological properties and understanding the impact of phage-bacteria interactions on human health. In this study, we provide an overview of the human gut phageome, including its composition, structure, and development. We also explore the various factors that may influence the phageome based on current research, including age, diet, ethnicity, and geographical location. Additionally, we summarize the relationship between the phageome and human diseases, such as IBD, IBS, obesity, diabetes, and metabolic syndrome.

Nonbacterial Microflora in Wastewater Treatment Plants: an Underappreciated Potential Source of Pathogens

Wastewater treatment plants (WWTPs) receive and treat large volumes of domestic, industrial, and urban wastewater containing pathogenic and nonpathogenic microorganisms, chemical compounds, heavy metals, and other potentially hazardous substances. WWTPs play an essential role in preserving human, animal, and environmental health by removing many of these toxic and infectious agents, particularly biological hazards. Wastewater contains complex consortiums of bacterial, viral, archaeal, and eukaryotic species, and while bacteria in WWTP have been extensively studied, the temporal and spatial distribution of nonbacterial microflora (viruses, archaea, and eukaryotes) is less understood. In this study, we analyzed the viral, archaeal, and eukaryotic microflora in wastewater throughout a treatment plant (raw influent, effluent, oxidation pond water, and oxidation pond sediment) in Aotearoa (New Zealand) using Illumina shotgun metagenomic sequencing. Our results suggest a similar trend across many taxa, with an increase in relative abundance in oxidation pond samples compared to influent and effluent samples, except for archaea, which had the opposite trend. Additionally, some microbial families, such as Podoviridae bacteriophages and Apicomplexa alveolates, appeared largely unaffected by the treatment process, with their relative abundance remaining stable throughout. Several groups encompassing pathogenic species, such as Leishmania, Plasmodium, Toxoplasma, Apicomplexa, Cryptococcus, Botrytis, and Ustilago, were identified. If present, these potentially pathogenic species could be a threat to human and animal health and agricultural productivity; therefore, further investigation is warranted. These nonbacterial pathogens should be considered when assessing the potential for vector transmission, distribution of biosolids to land, and discharge of treated wastewater to waterways or land. IMPORTANCE Nonbacterial microflora in wastewater remain understudied compared to their bacterial counterparts despite their importance in the wastewater treatment process. In this study, we report the temporal and spatial distributions of DNA viruses, archaea, protozoa, and fungi in raw wastewater influent, effluent, oxidation pond water, and oxidation pond sediments by using shotgun metagenomic sequencing. Our study indicated the presence of groups of nonbacterial taxa which encompass pathogenic species that may have potential to cause disease in humans, animals, and agricultural crops. We also observed higher alpha diversity in viruses, archaea, and fungi in effluent samples than in influent samples. This suggests that the resident microflora in the wastewater treatment plant may be making a greater contribution to the diversity of taxa observed in wastewater effluent than previously thought. This study provides important insights to better understand the potential human, animal, and environmental health impacts of discharged treated wastewater.

The Post-Antibiotic Era: A New Dawn for Bacteriophages

Phages are the most biologically diverse entities in the biosphere, infecting specific bacteria. Lytic phages quickly kill bacteria, while lysogenic phages integrate their genomes into bacteria and reproduce within the bacteria, participating in the evolution of natural populations. Thus, lytic phages are used to treat bacterial infections. However, due to the huge virus invasion, bacteria have also evolved a special immune mechanism (CRISPR-Cas systems, discovered in 1987). Therefore, it is necessary to develop phage cocktails and synthetic biology methods to infect bacteria, especially against multidrug-resistant bacteria infections, which are a major global threat. This review outlines the discovery and classification of phages and the associated achievements in the past century. The main applications of phages, including synthetic biology and PT, are also discussed, in addition to the effects of PT on immunity, intestinal microbes, and potential safety concerns. In the future, combining bioinformatics, synthetic biology, and classic phage research will be the way to deepen our understanding of phages. Overall, whether phages are an important element of the ecosystem or a carrier that mediates synthetic biology, they will greatly promote the progress of human society.

Structural atlas of a human gut crassvirus

CrAssphage and related viruses of the order Crassvirales (hereafter referred to as crassviruses) were originally discovered by cross-assembly of metagenomic sequences. They are the most abundant viruses in the human gut, are found in the majority of individual gut viromes, and account for up to 95% of the viral sequences in some individuals1-4. Crassviruses are likely to have major roles in shaping the composition and functionality of the human microbiome, but the structures and roles of most of the virally encoded proteins are unknown, with only generic predictions resulting from bioinformatic analyses4,5. Here we present a cryo-electron microscopy reconstruction of Bacteroides intestinalis virus ΦcrAss0016, providing the structural basis for the functional assignment of most of its virion proteins. The muzzle protein forms an assembly about 1 MDa in size at the end of the tail and exhibits a previously unknown fold that we designate the 'crass fold', that is likely to serve as a gatekeeper that controls the ejection of cargos. In addition to packing the approximately 103 kb of virus DNA, the ΦcrAss001 virion has extensive storage space for virally encoded cargo proteins in the capsid and, unusually, within the tail. One of the cargo proteins is present in both the capsid and the tail, suggesting a general mechanism for protein ejection, which involves partial unfolding of proteins during their extrusion through the tail. These findings provide a structural basis for understanding the mechanisms of assembly and infection of these highly abundant crassviruses.

iPHoP: An integrated machine learning framework to maximize host prediction for metagenome-derived viruses of archaea and bacteria

The extraordinary diversity of viruses infecting bacteria and archaea is now primarily studied through metagenomics. While metagenomes enable high-throughput exploration of the viral sequence space, metagenome-derived sequences lack key information compared to isolated viruses, in particular host association. Different computational approaches are available to predict the host(s) of uncultivated viruses based on their genome sequences, but thus far individual approaches are limited either in precision or in recall, i.e., for a number of viruses they yield erroneous predictions or no prediction at all. Here, we describe iPHoP, a two-step framework that integrates multiple methods to reliably predict host taxonomy at the genus rank for a broad range of viruses infecting bacteria and archaea, while retaining a low false discovery rate. Based on a large dataset of metagenome-derived virus genomes from the IMG/VR database, we illustrate how iPHoP can provide extensive host prediction and guide further characterization of uncultivated viruses.

Expanding known viral diversity in the healthy infant gut

The gut microbiome is shaped through infancy and impacts the maturation of the immune system, thus protecting against chronic disease later in life. Phages, or viruses that infect bacteria, modulate bacterial growth by lysis and lysogeny, with the latter being especially prominent in the infant gut. Viral metagenomes (viromes) are difficult to analyse because they span uncharted viral diversity, lacking marker genes and standardized detection methods. Here we systematically resolved the viral diversity in faecal viromes from 647 1-year-olds belonging to Copenhagen Prospective Studies on Asthma in Childhood 2010, an unselected Danish cohort of healthy mother-child pairs. By assembly and curation we uncovered 10,000 viral species from 248 virus family-level clades (VFCs). Most (232 VFCs) were previously unknown, belonging to the Caudoviricetes viral class. Hosts were determined for 79% of phage using clustered regularly interspaced short palindromic repeat spacers within bacterial metagenomes from the same children. Typical Bacteroides-infecting crAssphages were outnumbered by undescribed phage families infecting Clostridiales and Bifidobacterium. Phage lifestyles were conserved at the viral family level, with 33 virulent and 118 temperate phage families. Virulent phages were more abundant, while temperate ones were more prevalent and diverse. Together, the viral families found in this study expand existing phage taxonomy and provide a resource aiding future infant gut virome research.

A highly conserved and globally prevalent cryptic plasmid is among the most numerous mobile genetic elements in the human gut

Plasmids are extrachromosomal genetic elements that often encode fitness enhancing features. However, many bacteria carry 'cryptic' plasmids that do not confer clear beneficial functions. We identified one such cryptic plasmid, pBI143, which is ubiquitous across industrialized gut microbiomes, and is 14 times as numerous as crAssphage, currently established as the most abundant genetic element in the human gut. The majority of mutations in pBI143 accumulate in specific positions across thousands of metagenomes, indicating strong purifying selection. pBI143 is monoclonal in most individuals, likely due to the priority effect of the version first acquired, often from one's mother. pBI143 can transfer between Bacteroidales and although it does not appear to impact bacterial host fitness in vivo, can transiently acquire additional genetic content. We identified important practical applications of pBI143, including its use in identifying human fecal contamination and its potential as an inexpensive alternative for detecting human colonic inflammatory states.

Bacteriophages of the Order Crassvirales: What Do We Currently Know about This Keystone Component of the Human Gut Virome?

The order Crassvirales comprises dsDNA bacteriophages infecting bacteria in the phylum Bacteroidetes that are found in a variety of environments but are especially prevalent in the mammalian gut. This review summarises available information on the genomics, diversity, taxonomy, and ecology of this largely uncultured viral taxon. With experimental data available from a handful of cultured representatives, the review highlights key properties of virion morphology, infection, gene expression and replication processes, and phage-host dynamics.

Human virome: Implications in cancer

In recent years, the human virome has gained importance, especially after the SARS-CoV-2 pandemic, due to its possible involvement in autoimmune, inflammatory diseases, and cancer. Characterization of the human virome can be carried out by shotgun next-generation sequencing (metagenomics), which allows the identification of all viral communities in an environmental sample and the discovery of new viral families not previously described. Variations in viral quantity and diversity have been associated with disease development, mainly due to their effect on gut bacterial microbiota. Phages can regulate bacterial flora through lysogeny; this is associated with increased susceptibility to infections, chronic inflammation, or cancer. The virome characterization in different human body ecological niches could help elucidate these particles' role in disease. Hence, it is important to understand the virome's influence on human health and disease. The present review highlights the significance of the human virome and how it is associated with disease, focusing on virome composition, characterization, and its association with cancer.

Interpersonal variability of the human gut virome confounds disease signal detection in IBD

Viruses are increasingly recognised as important components of the human microbiome, fulfilling numerous ecological roles including bacterial predation, immune stimulation, genetic diversification, horizontal gene transfer, microbial interactions, and augmentation of metabolic functions. However, our current view of the human gut virome is tainted by previous sequencing requirements that necessitated the amplification of starting nucleic acids. In this study, we performed an original longitudinal analysis of 40 healthy control, 19 Crohn's disease, and 20 ulcerative colitis viromes over three time points without an amplification bias, which revealed and highlighted the interpersonal individuality of the human gut virome. In contrast to a 16 S rRNA gene analysis of matched samples, we show that α- and β-diversity metrics of unamplified viromes are not as efficient at discerning controls from patients with inflammatory bowel disease. Additionally, we explored the intrinsic properties of unamplified gut viromes and show there is considerable interpersonal variability in viral taxa, infrequent longitudinal persistence of intrapersonal viruses, and vast fluctuations in the abundance of temporal viruses. Together, these properties of unamplified faecal viromes confound the ability to discern disease associations but significantly advance toward an unbiased and accurate representation of the human gut virome.

CrAssphage May Be Viable Markers of Contamination in Pristine and Contaminated River Water

Viruses are the most biologically abundant entities and may be ideal indicators of fecal pollutants in water. Anthropogenic activities have triggered drastic ecosystem changes in rivers, leading to substantial shifts in chemical and biological attributes. Here, we evaluate the viability of using the presence of crAssphage as indicators of fecal contamination in South African rivers. Shotgun analysis revealed diverse crAssphage viruses in these rivers, which are impacted by chemical and biological pollution. Overall, the diversity and relative abundances of these viruses was higher in contaminated sites compared to pristine locations. In contrast to fecal coliform counts, crAssphage sequences were detected in pristine rivers, supporting the assertion that the afore mentioned marker may be a more accurate indicator of fecal contamination. Our data demonstrate the presence of diverse putative hosts which includes members of the phyla Bacteroidota, Pseudomonadota, Verrucomicrobiota, and Bacillota. Phylogenetic analysis revealed novel subfamilies, suggesting that rivers potentially harbor distinct and uncharacterized clades of crAssphage. These data provide the first insights regarding the diversity, distribution, and functional roles of crAssphage in rivers. Taken together, the results support the potential application of crAssphage as viable markers for water quality monitoring. IMPORTANCE Rivers support substantial populations and provide important ecosystem services. Despite the application of fecal coliform tests and other markers, we lack rapid and reproducible approaches for determining fecal contamination in rivers. Waterborne viral outbreaks have been reported even after fecal indicator bacteria (FIB) were suggested to be absent or below regulated levels of coliforms. This indicates a need to develop and apply improved indicators of pollutants in aquatic ecosystems. Here, we evaluate the viability of crAssphage as indicators of fecal contamination in two South African rivers. We assess the abundance, distribution, and diversity of these viruses in sites that had been predicted pristine or contaminated by FIB analysis. We show that crAssphage are ideal and sensitive markers for fecal contamination and describe novel clades of crAss-like phages. Known crAss-like subfamilies were unrepresented in our data, suggesting that the diversity of these viruses may reflect geographic locality and dependence.

The Human Gut Virome and Its Relationship with Nontransmissible Chronic Diseases

The human gastrointestinal tract contains large communities of microorganisms that are in constant interaction with the host, playing an essential role in the regulation of several metabolic processes. Among the gut microbial communities, the gut bacteriome has been most widely studied in recent decades. However, in recent years, there has been increasing interest in studying the influences that other microbial groups can exert on the host. Among them, the gut virome is attracting great interest because viruses can interact with the host immune system and metabolic functions; this is also the case for phages, which interact with the bacterial microbiota. The antecedents of virome-rectification-based therapies among various diseases were also investigated. In the near future, stool metagenomic investigation should include the identification of bacteria and phages, as well as their correlation networks, to better understand gut microbiota activity in metabolic disease progression.

Diverse viruses of marine archaea discovered using metagenomics

During the past decade, metagenomics became a method of choice for the discovery of novel viruses. However, host assignment for uncultured viruses remains challenging, especially for archaeal viruses, which are grossly undersampled compared to viruses of bacteria and eukaryotes. Here, we assessed the utility of CRISPR spacer targeting, tRNA gene matching and homology searches for viral signature proteins, such as major capsid proteins, for the assignment of archaeal hosts and validated these approaches on metaviromes from Yangshan Harbor (YSH). We report 35 new genomes of viruses which could be confidently assigned to hosts representing diverse lineages of marine archaea. We show that the archaeal YSH virome is highly diverse, with some viruses enriching the previously described virus groups, such as magroviruses of Marine Group II Archaea (Poseidoniales), and others representing novel groups of marine archaeal viruses. Metagenomic recruitment of Tara Oceans datasets on the YSH viral genomes demonstrated the presence of YSH Poseidoniales and Nitrososphaeria viruses in the global oceans, but also revealed the endemic YSH-specific viral lineages. Furthermore, our results highlight the relationship between the soil and marine thaumarchaeal viruses. We propose three new families within the class Caudoviricetes for the classification of the five complete viral genomes predicted to replicate in marine Poseidoniales and Nitrososphaeria, two ecologically important and widespread archaeal groups. This study illustrates the utility of viral metagenomics in exploring the archaeal virome and provides new insights into the diversity, distribution and evolution of marine archaeal viruses.

Abolishment of morphology-based taxa and change to binomial species names: 2022 taxonomy update of the ICTV bacterial viruses subcommittee

This article summarises the activities of the Bacterial Viruses Subcommittee of the International Committee on Taxonomy of Viruses for the period of March 2021-March 2022. We provide an overview of the new taxa proposed in 2021, approved by the Executive Committee, and ratified by vote in 2022. Significant changes to the taxonomy of bacterial viruses were introduced: the paraphyletic morphological families Podoviridae, Siphoviridae, and Myoviridae as well as the order Caudovirales were abolished, and a binomial system of nomenclature for species was established. In addition, one order, 22 families, 30 subfamilies, 321 genera, and 862 species were newly created, promoted, or moved.

PhaTYP: predicting the lifestyle for bacteriophages using BERT

Bacteriophages (or phages), which infect bacteria, have two distinct lifestyles: virulent and temperate. Predicting the lifestyle of phages helps decipher their interactions with their bacterial hosts, aiding phages' applications in fields such as phage therapy. Because experimental methods for annotating the lifestyle of phages cannot keep pace with the fast accumulation of sequenced phages, computational method for predicting phages' lifestyles has become an attractive alternative. Despite some promising results, computational lifestyle prediction remains difficult because of the limited known annotations and the sheer amount of sequenced phage contigs assembled from metagenomic data. In particular, most of the existing tools cannot precisely predict phages' lifestyles for short contigs. In this work, we develop PhaTYP (Phage TYPe prediction tool) to improve the accuracy of lifestyle prediction on short contigs. We design two different training tasks, self-supervised and fine-tuning tasks, to overcome lifestyle prediction difficulties. We rigorously tested and compared PhaTYP with four state-of-the-art methods: DeePhage, PHACTS, PhagePred and BACPHLIP. The experimental results show that PhaTYP outperforms all these methods and achieves more stable performance on short contigs. In addition, we demonstrated the utility of PhaTYP for analyzing the phage lifestyle on human neonates' gut data. This application shows that PhaTYP is a useful means for studying phages in metagenomic data and helps extend our understanding of microbial communities.

Use of an Integrated Approach Involving AlphaFold Predictions for the Evolutionary Taxonomy of Duplodnaviria Viruses

The evaluation of the evolutionary relationships is exceptionally important for the taxonomy of viruses, which is a rapidly expanding area of research. The classification of viral groups belonging to the realm Duplodnaviria, which include tailed bacteriophages, head-tailed archaeal viruses and herpesviruses, has undergone many changes in recent years and continues to improve. One of the challenging tasks of Duplodnaviria taxonomy is the classification of high-ranked taxa, including families and orders. At the moment, only 17 of 50 families have been assigned to orders. The evaluation of the evolutionary relationships between viruses is complicated by the high level of divergence of viral proteins. However, the development of structure prediction algorithms, including the award-winning AlphaFold, encourages the use of the results of structural predictions to clarify the evolutionary history of viral proteins. In this study, the evolutionary relationships of two conserved viral proteins, the major capsid protein and terminase, representing different viruses, including all classified Duplodnaviria families, have been analysed using AlphaFold modelling. This analysis has been undertaken using structural comparisons and different phylogenetic methods. The results of the analyses mainly indicated the high quality of AlphaFold modelling and the possibility of using the AlphaFold predictions, together with other methods, for the reconstruction of the evolutionary relationships between distant viral groups. Based on the results of this integrated approach, assumptions have been made about refining the taxonomic classification of bacterial and archaeal Duplodnaviria groups, and problems relating to the taxonomic classification of Duplodnaviria have been discussed.

The Two-Faced Role of crAssphage Subfamilies in Obesity and Metabolic Syndrome: Between Good and Evil

Viral metagenomic studies of the human gut microbiota have unraveled the differences in phage populations between health and disease, stimulating interest in phages' role on bacterial ecosystem regulation. CrAssphage is a common and abundant family in the gut virome across human populations. Therefore, we explored its role in obesity (O) and obesity with metabolic syndrome (OMS) in a children's cohort. We found a significantly decreased prevalence, diversity, and richness of the crAssphage Alpha subfamily in OMS mainly driven by a decrease in the Alpha_1 and Alpha_4 genera. On the contrary, there was a significant increase in the Beta subfamily in OMS, mainly driven by an increase in Beta_6. Additionally, an overabundance of the Delta_8 genus was observed in OMS. Notably, a decreased abundance of crAssphages was significantly correlated with the overabundance of Bacilli in the same group. The Bacilli class is a robust taxonomical biomarker of O and was also significantly abundant in our OMS cohort. Our results suggest that a loss of stability in the Alpha subfamily of crAssphages is associated with O and OMS. Contrary, an overabundance of the Delta subfamily was found in OMS. Our study advises the importance of considering the dual role (good and evil) of crAssphage subfamilies and their participation in conditions such as O, where we suggest that Alpha loss and Delta gain are associated with obese individuals.

Metagenome data-based phage therapy for intestinal bacteria-mediated diseases

Improvements in genome analysis technology using next-generation sequencing have revealed that abnormalities in the composition of the intestinal microbiota are important in numerous diseases. Furthermore, intestinal commensal pathogens that are directly involved in the onset and exacerbation of disease have been identified. Specific control of them is strongly desired. However, antibiotics are not appropriate for the control of intestinal commensal pathogens because they may kill beneficial bacteria as well. The intestinal tract contains many viruses: most are bacteriophages (phages) that infect intestinal bacteria rather than viruses that infect human cells. Phages have very high specificity for their host bacteria. Therefore, phage therapy is considered potentially useful for controlling intestinal commensal pathogens. However, the intestinal tract is a specialized, anaerobic environment, and it is impossible to isolate phages that infect host intestinal bacteria if the bacteria cannot be cultured. Furthermore, genomic analysis methods for intestinal phages have not been well established, so until recently, a complete picture of the intestinal phage has not been clear. In this review, I summarize the importance of next-generation phage therapy based on metagenomic data and describe a novel therapy against Clostridioides difficile developed using such data.

Multiomic spatial analysis reveals a distinct mucosa-associated virome

The human gut virome has been increasingly explored in recent years. However, nearly all virome-sequencing efforts rely solely on fecal samples and few studies leverage multiomic approaches to investigate phage-host relationships. Here, we combine metagenomics, metaviromics, and metatranscriptomics to study virome-bacteriome interactions at the colonic mucosal-luminal interface in a cohort of three individuals with inflammatory bowel disease; non-IBD controls were not included in this study. We show that the mucosal viral population is distinct from the stool virome and houses abundant crAss-like phages that are undetectable by fecal sampling. Through viral protein prediction and metatranscriptomic analysis, we explore viral gene transcription, prophage activation, and the relationship between the presence of integrase and temperate phages in IBD subjects. We also show the impact of deep sequencing on virus recovery and offer guidelines for selecting optimal sequencing depths in future metaviromic studies. Systems biology approaches such as those presented in this report will enhance our understanding of the human virome and its interactions with our microbiome and our health.

The global virome: How much diversity and how many independent origins?

Viruses are considered to be the most abundant biological entities on earth. They also display striking genetic diversity as emphatically demonstrated by the recent advances of metagenomics and metatranscriptomics. But what are the limits of this diversity, that is, how many virus species in the earth virome? By combining the available estimates of the number of prokaryote species with those of the virome size, we obtain back-of-the-envelope estimates of the total number of distinct virus species, which come out astronomically large, from about 10⁷ to about 10⁹ . The route of virus origins apparently involved non-viral replicators capturing and exapting various cellular proteins to become virus capsid subunits. How many times in the history of life has this happened? In other words, how many realms of viruses, the highest rank taxa that are supposed to be monophyletic, comprise the global virome? We argue that viruses emerged on a number (even if far from astronomical) independent occasions, so the number of realms will considerably increase from the current 6, by splitting some of the current realms, giving the realm status to some of the currently unclassified groups of viruses and discovery of new distinct groups.

Prokaryotic and viral genomes recovered from 787 Japanese gut metagenomes revealed microbial features linked to diets, populations, and diseases

We reconstructed 19,084 prokaryotic and 31,395 viral genomes from 787 Japanese gut metagenomes as Japanese metagenome-assembled genomes (JMAG) and Japanese Virus Database (JVD), which are large microbial genome datasets for a single population. Population-specific enrichment of the Bacillus subtilis and β-porphyranase among the JMAG could derive from the Japanese traditional food natto (fermented soybeans) and nori (laver), respectively. Dairy-related Enterococcus_B lactis and Streptococcus thermophilus were nominally associated with the East Asian-specific missense variant rs671:G>A in ALDH2, which was associated with dairy consumption. Of the species-level viral genome clusters in the JVD, 62.9% were novel. The β crAss-like phage composition was low among the Japanese but relatively high among African and Oceanian peoples. Evaluations of the association between crAss-like phages and diseases showed significant disease-specific associations. Our large catalog of virus-host pairs identified the positive correlation between the abundance of the viruses and their hosts.

Characterization of the human gut virome in metabolic and autoimmune diseases

The intestinal microbiome is dominated by bacteria and plays a pivotal role in the occurrence and development of disease, including several metabolic and autoimmune disorders. While intestinal viral communities, primarily made up of bacteriophages, are also thought to play a role in disease pathogenesis in the gastrointestinal tract, they have received much less attention than intestinal bacteria. Thus, there is limited information about the relationship between bacteriophages and disease. This review explores a potential role for the intestinal viral microbiome in various metabolic and autoimmune diseases.

Understanding Bacteriophage Tail Fiber Interaction with Host Surface Receptor: The Key “Blueprint” for Reprogramming Phage Host Range

Bacteriophages (phages), as natural antibacterial agents, are being rediscovered because of the growing threat of multi- and pan-drug-resistant bacterial pathogens globally. However, with an estimated 10³¹ phages on the planet, finding the right phage to recognize a specific bacterial host is like looking for a needle in a trillion haystacks. The host range of a phage is primarily determined by phage tail fibers (or spikes), which initially mediate reversible and specific recognition and adsorption by susceptible bacteria. Recent significant advances at single-molecule and atomic levels have begun to unravel the structural organization of tail fibers and underlying mechanisms of phage–host interactions. Here, we discuss the molecular mechanisms and models of the tail fibers of the well-characterized T4 phage’s interaction with host surface receptors. Structure–function knowledge of tail fibers will pave the way for reprogramming phage host range and will bring future benefits through more-effective phage therapy in medicine. Furthermore, the design strategies of tail fiber engineering are briefly summarized, including machine-learning-assisted engineering inspired by the increasingly enormous amount of phage genetic information.

Unraveling the viral dark matter through viral metagenomics

Viruses are part of the microbiome and have essential roles in immunology, evolution, biogeochemical cycles, health, and disease progression. Viruses influence a wide variety of systems and processes, and the continued discovery of novel viruses is anticipated to reveal new mechanisms influencing the biology of diverse environments. While the identity and roles of viruses continue to be discovered and understood through viral metagenomics, most of the sequences in virome datasets cannot be attributed to known viruses or may be only distantly related to species already described in public sequence databases, at best. Such viruses are known as the viral dark matter. Ongoing discoveries from the viral dark matter have provided insights into novel viruses from a variety of environments, as well as their potential in immunological processes, virus evolution, health, disease, therapeutics, and surveillance. Increased understanding of the viral dark matter will continue with a combination of cultivation, microscopy, sequencing, and bioinformatic efforts, which are discussed in the present review.

Extensive gut virome variation and its associations with host and environmental factors in a population-level cohort

Indigenous bacteriophage communities (virome) in the human gut have a huge impact on the structure and function of gut bacterial communities (bacteriome), but virome variation at a population scale is not fully investigated yet. Here, we analyse the gut dsDNA virome in the Japanese 4D cohort of 4198 deeply phenotyped individuals. By assembling metagenomic reads, we discover thousands of high-quality phage genomes including previously uncharacterised phage clades with different bacterial hosts than known major ones. The distribution of host bacteria is a strong determinant for the distribution of phages in the gut, and virome diversity is highly correlated with anti-viral defence mechanisms of the bacteriome, such as CRISPR-Cas and restriction-modification systems. We identify 97 various intrinsic/extrinsic factors that significantly affect the virome structure, including age, sex, lifestyle, and diet, most of which showed consistent associations with both phages and their predicted bacterial hosts. Among the metadata categories, disease and medication have the strongest effects on the virome structure. Overall, these results present a basis to understand the symbiotic communities of bacteria and their viruses in the human gut, which will facilitate the medical and industrial applications of indigenous viruses.

Here, Nishijima et al. perform a large-scale analysis of the human gut virome in the Japanese 4D cohort of 4198 deeply phenotyped individuals, revealing thousands of bacteriophage genomes, virus-bacteria interactions, and describing associations with various host and environmental factors.

Varidnaviruses in the Human Gut: A Major Expansion of the Order Vinavirales

Bacteriophages play key roles in the dynamics of the human microbiome. By far the most abundant components of the human gut virome are tailed bacteriophages of the realm Duplodnaviria, in particular, crAss-like phages. However, apart from duplodnaviruses, the gut virome has not been dissected in detail. Here we report a comprehensive census of a minor component of the gut virome, the tailless bacteriophages of the realm Varidnaviria. Tailless phages are primarily represented in the gut by prophages, that are mostly integrated in genomes of Alphaproteobacteria and Verrucomicrobia and belong to the order Vinavirales, which currently consists of the families Corticoviridae and Autolykiviridae. Phylogenetic analysis of the major capsid proteins (MCP) suggests that at least three new families should be established within Vinavirales to accommodate the diversity of prophages from the human gut virome. Previously, only the MCP and packaging ATPase genes were reported as conserved core genes of Vinavirales. Here we report an extended core set of 12 proteins, including MCP, packaging ATPase, and previously undetected lysis enzymes, that are shared by most of these viruses. We further demonstrate that replication system components are frequently replaced in the genomes of Vinavirales, suggestive of selective pressure for escape from yet unknown host defenses or avoidance of incompatibility with coinfecting related viruses. The results of this analysis show that, in a sharp contrast to marine viromes, varidnaviruses are a minor component of the human gut virome. Moreover, they are primarily represented by prophages, as indicated by the analysis of the flanking genes, suggesting that there are few, if any, lytic varidnavirus infections in the gut at any given time. These findings complement the existing knowledge of the human gut virome by exploring a group of viruses that has been virtually overlooked in previous work.