Advances and challenges in cataloging the human gut virome

The Aggregated Gut Viral Catalogue (AVrC): A unified resource for exploring the viral diversity of the human gut

The growing interest in the role of the gut virome in human health and disease, has led to several recent large-scale viral catalogue projects mining human gut metagenomes each using varied computational tools and quality control criteria. Importantly, there has been to date no consistent comparison of these catalogues' quality, diversity, and overlap. In this project, we therefore systematically surveyed nine previously published human gut viral catalogues. While these catalogues collectively screened >40,000 human fecal metagenomes, 82% of the recovered 345,613 viral sequences were unique to one catalogue, highlighting limited redundancy between the ressources and suggesting the need for an aggregated resource bringing these viral sequences together. We further expanded these viral catalogues by mining 7,867 infant gut metagenomes from 12 large-scale infant studies collected in 9 different countries. From these datasets, we constructed the Aggregated Gut Viral Catalogue (AVrC), a unified modular resource containing 1,018,941 dereplicated viral sequences (449,859 species-level vOTUs). Using computational inference tools, annotations were obtained for each vOTU representative sequence quality, viral taxonomy, predicted viral lifestyle, and putative host. This project aims to facilitate the reuse of previously published viral catalogues by the research community and follows a modular framework to enable future expansions as novel data becomes available.

A bacteriophage-conditional mouse model reveals the impact of phages within a conventionally colonized gut microbiota

The significance of bacteriophages in the gut microbiota remains poorly understood due, in part, to an absence of an animal model that allows for comparative study of conditions with or without phages while retaining the microbial diversity attained by conventional colonization. We describe a mouse model that uses a broadly available chemical compound, acriflavine, to preferentially deplete virulent phages from the gut without significantly impacting gut bacteria. We then show that gut phage density can be reconstituted by oral gavage. Using this bacteriophage-conditional (BaCon) mouse model, we reveal that while phages have comparatively minimal impact during equilibrium conditions, they increase the potency of ampicillin against commensal gut bacteria. Collectively, our work presents an animal model that can be leveraged to conditionally study the role of phages in complex, physiologically relevant systems and further identifies virulent gut phages as potential sources of bacterial variability during major perturbations.

Characterization of the phyllosphere virome of fresh vegetables and potential transfer to the human gut

Fresh vegetables harbor diverse microorganisms on leaf surfaces, yet their viral communities remain unexplored. We investigate the diversity and ecology of phyllosphere viromes of six leafy green vegetables using virus-like particle (VLP) enrichment and shotgun metagenome sequencing. On average, 9.2 × 107 viruses are present per gram of leaf tissue. The majority (93.1 ± 6.2%) of these viruses are taxonomically unclassified. Virome compositions are distinct among vegetable types and exhibit temporal variations. Virulent phages with replication-enhancing auxiliary metabolic genes (AMGs) are more dominant than temperate phages with host fitness-benefiting AMGs. Analysis of 1498 human fecal VLP metagenomes reveals that approximately 10% of vegetable viruses are present in the human gut virome, including viruses commonly observed in multiple studies. These gut-associated vegetable viruses are enriched with short-term vegetable intake, and depleted in individuals with metabolic and immunologic disorders. Overall, this study elucidates the ecological contribution of the fresh vegetable virome to human gut virome diversity.

The Chinese gut virus catalogue reveals gut virome diversity and disease-related viral signatures

BACKGROUND

The gut viral community has been increasingly recognized for its role in human physiology and health; however, our understanding of its genetic makeup, functional potential, and disease associations remains incomplete.

METHODS

In this study, we collected 11,286 bulk or viral metagenomes from fecal samples across large-scale Chinese populations to establish a Chinese Gut Virus Catalogue (cnGVC) using a de novo virus identification approach. We then examined the diversity and compositional patterns of the gut virome in relation to common diseases by analyzing 6311 bulk metagenomes representing 28 disease or unhealthy states.

RESULTS

The cnGVC contains 93,462 nonredundant viral genomes, with over 70% of these being novel viruses not included in existing gut viral databases. This resource enabled us to characterize the functional diversity and specificity of the gut virome. Using cnGVC, we profiled the gut virome in large-scale populations, assessed sex- and age-related variations, and identified 4238 universal viral signatures of diseases. A random forest classifier based on these signatures achieved high accuracy in distinguishing diseased individuals from controls (AUC = 0.698) and high-risk patients from controls (AUC = 0.761), and its predictive ability was also validated in external cohorts.

CONCLUSIONS

Our resources and findings significantly expand the current understanding of the human gut virome and provide a comprehensive view of the associations between gut viruses and common diseases. This will pave the way for novel strategies in the treatment and prevention of these diseases.

A roadmap of isolating and investigating bacteriophage infecting human gut anaerobes

Bacteriophages, viruses that infect bacteria, play a crucial role in manipulating the gut microbiome, with implications for human health and disease. Despite the vast amount of data available on the human gut virome, the number of cultured phages that infect human gut bacteria-particularly obligate anaerobes-remains strikingly limited. Here, we summarize the resources and basic characteristics of phages that infect the human gut obligate anaerobe. We review various methods for isolating these phages and suggest a strategy for their isolation. Additionally, we outline their impact on the field of viral biology, their interactions with bacteria and humans, and their potential for disease intervention. Finally, we discuss the value and prospects of research on these phages, providing a comprehensive 'Roadmap' that sheds light on the 'dark matter' of phages that infect human gut obligate anaerobes.

A metagenome-assembled genome inventory for children reveals early-life gut bacteriome and virome dynamics

Existing microbiota databases are biased toward adult samples, hampering accurate profiling of the infant gut microbiome. Here, we generated a metagenome-assembled genome inventory for children (MAGIC) from a large collection of bulk and viral-like particle-enriched metagenomes from 0 to 7 years of age, encompassing 3,299 prokaryotic and 139,624 viral species-level genomes, 8.5% and 63.9% of which are unique to MAGIC. MAGIC improves early-life microbiome profiling, with the greatest improvement in read mapping observed in Africans. We then identified 54 candidate keystone species, including several Bifidobacterium spp. and four phages, forming guilds that fluctuated in abundance with time. Their abundances were reduced in preterm infants and were associated with childhood allergies. By analyzing the B. longum pangenome, we found evidence of phage-mediated evolution and quorum sensing-related ecological adaptation. Together, the MAGIC database recovers genomes that enable characterization of the dynamics of early-life microbiomes, identification of candidate keystone species, and strain-level study of target species.

Exploring micronutrients and microbiome synergy: pioneering new paths in cancer therapy

The human microbiome is the complex ecosystem consisting of trillions of microorganisms that play a key role in developing the immune system and nutrient metabolism. Alterations in the gut microbiome have been linked to cancer initiation, progression, metastasis, and response to treatment. Accumulating evidence suggests that levels of vitamins and minerals influence the gut environment and may have implications for cancer risk and progression. Bifidobacterium has been reported to reduce the colorectal cancer risk by binding to free iron. Additionally, zinc ions have been shown to activate the immune cells and enhance the effectiveness of immunotherapy. Higher selenium levels have been associated with a reduced risk of several cancers, including colorectal cancer. In contrast, enhanced copper uptake has been implicated in promoting cancer progression, including colon cancer. The interaction between cancer and gut bacteria, as well as dysbiosis impact has been studied in animal models. The interplay between prebiotics, probiotics, synbiotics, postbiotics and gut bacteria in cancer offers the diverse physiological benefits. We also explored the particular probiotic formulations like VSL#3, Prohep, Lactobacillus rhamnosus GG (LGG), etc., for their ability to modulate immune responses and reduce tumor burden in preclinical models. Targeting the gut microbiome through antibiotics, bacteriophage, microbiome transplantation-based therapies will offer a new perspective in cancer research. Hence, to understand this interplay, we outline the importance of micronutrients with an emphasis on the immunomodulatory function of the microbiome and highlight the microbiome's potential as a target for precision medicine in cancer treatment.

A review of bacteriophage and their application in domestic animals in a post-antibiotic era

Bacteriophages (phages for short) are the most abundant biological entities on Earth and are natural enemies of bacteria. Genomics and molecular biology have identified subtle and complex relationships among phages, bacteria and their animal hosts. This review covers composition, diversity and factors affecting gut phage, their lifecycle in the body, and interactions with bacteria and hosts. In addition, research regarding phage in poultry, aquaculture and livestock are summarized, and application of phages in antibiotic substitution, phage therapy and food safety are reviewed.

Another piece of 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 the lack 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 and 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.

Gut virome-wide association analysis identifies cross-population viral signatures for inflammatory bowel disease

BACKGROUND

The gut virome has been implicated in inflammatory bowel disease (IBD), yet a full understanding of the gut virome in IBD patients, especially across diverse geographic populations, is lacking.

RESULTS

In this study, we conducted a comprehensive gut virome-wide association study in a Chinese cohort of 71 IBD patients (15 with Crohn's disease and 56 with ulcerative colitis) and 77 healthy controls via viral-like particle (VLP) and bulk virome sequencing of their feces. By utilizing an integrated gut virus catalog tailored to the IBD virome, we revealed fundamental alterations in the gut virome in IBD patients. These characterized 139 differentially abundant viral signatures, including elevated phages predicted to infect Escherichia, Klebsiella, Enterococcus_B, Streptococcus, and Veillonella species, as well as IBD-depleted phages targeting Prevotella, Ruminococcus_E, Bifidobacterium, and Blautia species. Remarkably, these viral signatures demonstrated high consistency across diverse populations such as those in Europe and the USA, emphasizing their significance and broad relevance in the disease context. Furthermore, fecal virome transplantation experiments verified that the colonization of these IBD-characterized viruses can modulate experimental colitis in mouse models.

CONCLUSIONS

Building upon these insights into the IBD gut virome, we identified potential biomarkers for prognosis and therapy in IBD patients, laying the foundation for further exploration of viromes in related conditions. Video Abstract.

A compendium of ruminant gastrointestinal phage genomes revealed a higher proportion of lytic phages than in any other environments

BACKGROUND

Ruminants are important livestock animals that have a unique digestive system comprising multiple stomach compartments. Despite significant progress in the study of microbiome in the gastrointestinal tract (GIT) sites of ruminants, we still lack an understanding of the viral community of ruminants. Here, we surveyed its viral ecology using 2333 samples from 10 sites along the GIT of 8 ruminant species.

RESULTS

We present the Unified Ruminant Phage Catalogue (URPC), a comprehensive survey of phages in the GITs of ruminants including 64,922 non-redundant phage genomes. We characterized the distributions of the phage genomes in different ruminants and GIT sites and found that most phages were organism-specific. We revealed that ~ 60% of the ruminant phages were lytic, which was the highest as compared with those in all other environments and certainly will facilitate their applications in microbial interventions. To further facilitate the future applications of the phages, we also constructed a comprehensive virus-bacteria/archaea interaction network and identified dozens of phages that may have lytic effects on methanogenic archaea.

CONCLUSIONS

The URPC dataset represents a useful resource for future microbial interventions to improve ruminant production and ecological environmental qualities. Phages have great potential for controlling pathogenic bacterial/archaeal species and reducing methane emissions. Our findings provide insights into the virome ecology research of the ruminant GIT and offer a starting point for future research on phage therapy in ruminants. Video Abstract.

Intestinal flora and pregnancy complications: Current insights and future prospects

Numerous studies have demonstrated the pivotal roles of intestinal microbiota in many physiopathological processes through complex interactions with the host. As a unique period in a woman's lifespan, pregnancy is characterized by changes in hormones, immunity, and metabolism. The gut microbiota also changes during this period and plays a crucial role in maintaining a healthy pregnancy. Consequently, anomalies in the composition and function of the gut microbiota, namely, gut microbiota dysbiosis, can predispose individuals to various pregnancy complications, posing substantial risks to both maternal and neonatal health. However, there are still many controversies in this field, such as "sterile womb" versus "in utero colonization." Therefore, a thorough understanding of the roles and mechanisms of gut microbiota in pregnancy and its complications is essential to safeguard the health of both mother and child. This review provides a comprehensive overview of the changes in gut microbiota during pregnancy, its abnormalities in common pregnancy complications, and potential etiological implications. It also explores the potential of gut microbiota in diagnosing and treating pregnancy complications and examines the possibility of gut-derived bacteria residing in the uterus/placenta. Our aim is to expand knowledge in maternal and infant health from the gut microbiota perspective, aiding in developing new preventive and therapeutic strategies for pregnancy complications based on intestinal microecology.

Synergistic horizontal transfer of antibiotic resistance genes and transposons in the infant gut microbial genome

Transposons, plasmids, bacteriophages, and other mobile genetic elements facilitate horizontal gene transfer in the gut microbiota, allowing some pathogenic bacteria to acquire antibiotic resistance genes (ARGs). Currently, the relationship between specific ARGs and specific transposons in the comprehensive infant gut microbiome has not been elucidated. In this study, ARGs and transposons were annotated from the Unified Human Gastrointestinal Genome (UHGG) and the Early-Life Gut Genomes (ELGG). Association rules mining was used to explore the association between specific ARGs and specific transposons in UHGG, and the robustness of the association rules was validated using the external database in ELGG. Our results suggested that ARGs and transposons were more likely to be relevant in infant gut microbiota compared to adult gut microbiota, and nine robust association rules were identified, among which Klebsiella pneumoniae, Enterobacter hormaechei_A, and Escherichia coli_D played important roles in this association phenomenon. The emphasis of this study is to investigate the synergistic transfer of specific ARGs and specific transposons in the infant gut microbiota, which can contribute to the study of microbial pathogenesis and the ARG dissemination dynamics.IMPORTANCEThe transfer of transposons carrying antibiotic resistance genes (ARGs) among microorganisms accelerates antibiotic resistance dissemination among infant gut microbiota. Nonetheless, it is unclear what the relationship between specific ARGs and specific transposons within the infant gut microbiota. K. pneumoniae, E. hormaechei_A, and E. coli_D were identified as key players in the nine robust association rules we discovered. Meanwhile, we found that infant gut microorganisms were more susceptible to horizontal gene transfer events about specific ARGs and specific transposons than adult gut microorganisms. These discoveries could enhance the understanding of microbial pathogenesis and the ARG dissemination dynamics within the infant gut microbiota.

Infant gut DNA bacteriophage strain persistence during the first 3 years of life

Bacteriophages are key components of gut microbiomes, yet the phage colonization process in the infant gut remains uncertain. Here, we establish a large phage sequence database and use strain-resolved analyses to investigate DNA phage succession in infants throughout the first 3 years of life. Analysis of 819 fecal metagenomes collected from 28 full-term and 24 preterm infants and their mothers revealed that early-life phageome richness increases over time and reaches adult-like complexity by age 3. Approximately 9% of early phage colonizers, which are mostly maternally transmitted and infect Bacteroides, persist for 3 years and are more prevalent in full-term than in preterm infants. Although rare, phages with stop codon reassignment are more likely to persist than non-recoded phages and generally display an increase in in-frame reassigned stop codons over 3 years. Overall, maternal seeding, stop codon reassignment, host CRISPR-Cas locus prevalence, and diverse phage populations contribute to stable viral colonization.

Gut virome in inflammatory bowel disease and beyond

OBJECTIVE

The gut virome is a dense community of viruses inhabiting the gastrointestinal tract and an integral part of the microbiota. The virome coexists with the other components of the microbiota and with the host in a dynamic equilibrium, serving as a key contributor to the maintenance of intestinal homeostasis and functions. However, this equilibrium can be interrupted in certain pathological states, including inflammatory bowel disease, causing dysbiosis that may participate in disease pathogenesis. Nevertheless, whether virome dysbiosis is a causal or bystander event requires further clarification.

DESIGN

This review seeks to summarise the latest advancements in the study of the gut virome, highlighting its cross-talk with the mucosal microenvironment. It explores how cutting-edge technologies may build upon current knowledge to advance research in this field. An overview of virome transplantation in diseased gastrointestinal tracts is provided along with insights into the development of innovative virome-based therapeutics to improve clinical management.

RESULTS

Gut virome dysbiosis, primarily driven by the expansion of Caudovirales, has been shown to impact intestinal immunity and barrier functions, influencing overall intestinal homeostasis. Although emerging innovative technologies still need further implementation, they display the unprecedented potential to better characterise virome composition and delineate its role in intestinal diseases.

CONCLUSIONS

The field of gut virome is progressively expanding, thanks to the advancements of sequencing technologies and bioinformatic pipelines. These have contributed to a better understanding of how virome dysbiosis is linked to intestinal disease pathogenesis and how the modulation of virome composition may help the clinical intervention to ameliorate gut disease management.

The Diversity of Bacteriophages in the Human Gut

Bacteriophages, commonly referred to as phages, are viruses that infect bacteria and are among the most numerous microorganisms on the planet. They occur throughout nature occupying every habitat where their bacterial hosts can be found. Within these communities, phages are responsible for shaping the bacterial community structure and function through their interactions. Phages shape the community structure and function within the human gut but are also able to influence the human host. As such, there is increased interest in understanding the composition and activity of the gastrointestinal phages, although these studies have been hindered by the difficulties accompanying the study of the human gut. Here, we summarize the methods and findings pertaining to the diversity of the human gastrointestinal phages.

A universe of human gut-derived bacterial prophages: unveiling the hidden viral players in intestinal microecology

Prophages, which are an existing form of temperate phages that integrate into host genomes, have been found extensively present in diverse bacterial species. The human gut microbiome, characterized by its complexity, dynamism, and interconnectivity among multiple species, remains inadequately understood in terms of the global landscape of bacterial prophages. Here, we analyzed 43,942 human gut-derived bacterial genomes (439 species of 12 phyla) and identified 105,613 prophage regions in ~ 92% of them. 16254 complete prophages were distributed in ~ 24% of bacteria, indicating an extremely uneven prophage distribution across various species within the human gut. Among all identified prophages, ~4% possessed cross-genera (2-20 genera) integration capacity, while ~ 17% displayed broad infection host ranges (targeting 2-35 genera). Functional gene annotation revealed that antibiotic-resistance genes and toxin-related genes were detected in ~ 2.5% and ~ 5.8% of all prophages, respectively. Furthermore, through sequence alignments between our obtained prophages and publicly available human gut phageome contigs, we have observed that ~ 72% of non-redundant prophages are previously unreported genomes, and they illuminate ~ 6.5-9.5% of the individual intestinal "viral dark matter". Our study represents the first comprehensive depiction of human gut-derived prophages, provides a substantial collection of reference sequences for forthcoming human gut phageome-related investigations, and potentially enables better risk assessment of prophage dissemination.

Colorectal cancer and gut viruses: a visualized analysis based on CiteSpace knowledge graph

Background

Gut microbiome is a complex community of microbes present in the human gut and plays an important role in the occurrence and progression of colorectal cancer (CRC). However, the relationship between virus and CRC has not been fully understood.

Objective

To explore the hot spots and research trends in the field of CRC and virus.

Methods

By using the bibliometric analysis tool CiteSpace and based on the articles of the Web of Science Core Collection (WoSCC) database, the country, institution, highly cited literature, keywords and so on were visually analyzed.

Results

A total of 356 research articles on CRC from 2001 to 2023 were thoroughly analyzed. The USA and China have made the largest contribution in the field of virus and CRC. The Helmholtz Association published the most papers. There were relatively few cooperations among institutions from different countries. The results of keyword cluster analysis proved that the literature on the relationship between human cytomegalovirus (CMV) and CRC was the most widely studied aspect in this field. "Gut microbiota," "inflammatory bowel disease," "hepatitis b virus," and "human papillomavirus infection" are the current research hotspots; "oncolytic virus," "apoptosis," and "gut microbiome" are the recent research frontiers and should be paid closer attention.

Conclusion

By using CiteSpace bibliometric software, the visual analysis reflected the research trends and hot topics of virus and CRC. In addition, the prevalence and mechanism of specific virus on CRC were also reviewed, which provides valuable references for future CRC research.

An extended catalog of integrated prophages in the infant and adult fecal microbiome shows high prevalence of lysogeny

Background and aims

The acquisition and gradual maturation of gut microbial communities during early childhood is central to an individual's healthy development. Bacteriophages have the potential to shape the gut bacterial communities. However, the complex ecological interactions between phages and their bacterial host are still poorly characterized. In this study, we investigated the abundance and diversity of integrated prophages in infant and adult gut bacteria by detecting integrated prophages in metagenome assembled genomes (MAGs) of commensal bacteria.

Methods

Our study included 88 infants sampled at 3 weeks, 3 months, 6 months, and 12 months (n = 323 total samples), and their parents around delivery time (n = 138 total samples). Fecal DNA was extracted and characterized by using shotgun metagenomic sequencing, and a collection of prokaryotic MAGs was generated. The MAG collection was screened for the presence of integrated bacteriophage sequences, allowing their taxonomic and functional characterization.

Results

A large collection of 6,186 MAGs from infant and adult gut microbiota was obtained and screened for integrated prophages, allowing the identification of 7,165 prophage sequences longer than 10 kb. Strikingly, more than 70% of the near-complete MAGs were identified as lysogens. The prevalence of prophages in MAGs varied across bacterial families, with a lower prevalence observed among Coriobacteriaceae, Eggerthellaceae, Veillonellaceae and Burkholderiaceae, while a very high prevalence of lysogen MAGs were observed in Oscillospiraceae, Enterococcaceae, and Enterobacteriaceae. Interestingly for several bacterial families such as Bifidobacteriaceae and Bacteroidaceae, the prevalence of prophages in MAGs was higher in early infant time point (3 weeks and 3 months) than in later sampling points (6 and 12 months) and in adults. The prophage sequences were clustered into 5,616 species-like vOTUs, 77% of which were novel. Finally, we explored the functional repertoire of the potential auxiliary metabolic genes carried by these prophages, encoding functions involved in carbohydrate metabolism and degradation, amino acid metabolism and carbon metabolism.

Conclusion

Our study provides an enhanced understanding of the diversity and prevalence of lysogens in infant and adult gut microbiota and suggests a complex interplay between prophages and their bacterial hosts.

Long-Read Sequencing Reveals Extensive DNA Methylations in Human Gut Phagenome Contributed by Prevalently Phage-Encoded Methyltransferases

DNA methylation plays a crucial role in the survival of bacteriophages (phages), yet the understanding of their genome methylation remains limited. In this study, DNA methylation patterns are analyzed in 8848 metagenome-assembled high-quality phages from 104 fecal samples using single-molecule real-time sequencing. The results demonstrate that 97.60% of gut phages exhibit methylation, with certain factors correlating with methylation densities. Phages with higher methylation densities appear to have potential viability advantages. Strikingly, more than one-third of the phages possess their own DNA methyltransferases (MTases). Increased MTase copies are associated with higher genome methylation densities, specific methylation motifs, and elevated prevalence of certain phage groups. Notably, the majority of these MTases share close homology with those encoded by gut bacteria, suggesting their exchange during phage-bacterium interactions. Furthermore, these MTases can be employed to accurately predict phage-host relationships. Overall, the findings indicate the widespread utilization of DNA methylation by gut DNA phages as an evasion mechanism against host defense systems, with a substantial contribution from phage-encoded MTases.

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.