VPF-Class: Taxonomic assignment and host prediction of uncultivated viruses based on viral protein families

Metagenomic analysis reveals ecological and functional signatures of oral phageome associated with severe early childhood caries

OBJECTIVES

Severe early childhood caries (S-ECC) is highly prevalent, affecting children's oral health. S-ECC development is closely associated with the complex oral microbial microbiome and its microorganism interactions, such as the imbalance of bacteriophages and bacteria. Till now, little is known about oral phageome on S-ECC. Therefore, this study aimed to investigate the potential role of the oral phageome in the pathogenesis of S-ECC.

METHODS

Unstimulated saliva (2 mL) was collected from 20 children with and without S-ECC for metagenomics analysis. Metagenomics sequencing and bioinformatic analysis were performed to determine the two groups' phageome diversity, taxonomic and functional annotations. Statistical analysis and visualization were performed with R and SPSS Statistics software.

RESULTS

85.7 % of the extracted viral sequences were predicted from phages, in which most phages were classified into Myoviridae, Siphoviridae, and Podoviridae. Alpha diversity decreased, and Beta diversity increased in the S-ECC phageome compared to the healthy group. The abundance of Podoviridae phages increased, and the abundance of Inoviridae, Herelleviridae, and Streptococcus phages decreased in the S-ECC group. Functional annotation revealed increased annotation on glycoside hydrolases and nucleotide metabolism, decreased glycosyl transferases, carbohydrate-binding modules, and biogenic metabolism in the S-ECC phageome.

CONCLUSIONS

Metagenomic analysis revealed reduced Streptococcus phages and significant changes in functional annotations within the S-ECC phageome. These findings suggest a potential weakening of the regulatory influence of oral bacteria, which may indicate the development of innovative prevention and treatment strategies for S-ECC. These implications deserve further investigation and hold promise for advancing our understanding and management of S-ECC.

CLINICAL SIGNIFICANCE

The findings of this study indicate that oral phageomes are associated with bacterial genomes and metabolic processes, affecting the development of S-ECC. The reduced modulatory effect of the oral phageome in counteracting S-ECC's cariogenic activity suggests a new avenue for the prevention and treatment of S-ECC.

Habitat- and lifestyle-dependent structural and functional characteristics of viruses in mangrove wetlands of different functional zonings

Mangrove wetlands, as one of the natural ecosystems with the most ecological services, have garnered widespread attention about their microbial driven biogeochemical cycling. Urbanization have led to different spatial patterns of environmental conditions and microbial communities in mangroves. However, viruses, as the pivotal drivers of biogeochemical cycling in mangroves, remain inadequately explored in terms of how their ecological potential and complex interactions with host respond to functional zonings. To address this knowledge gap, we conducted a comprehensive investigation on the structural and functional properties of temperate and lytic viruses in mangrove wetlands from different functional zonings by jointly using high-throughput sequencing, prokaryotic and viral metagenomics. Multiple environmental factors were found to significantly influence the taxonomic and functional composition, as well as lysogen-lysis decision-making of mangrove viruses. Furthermore, enriched auxiliary metabolic genes (AMGs) involved in methane, nitrogen and sulfur metabolism, and heavy metal resistance were unveiled in mangrove viruses, whose community composition was closely related to lifestyle and host. The virus-host pairs with different lifestyles were also discovered to react to environmental changes in different ways, which provided an empirical evidence for how virus and bacteria dynamics were specific to viral lifestyles in nature. This study expands our comprehension of the intricate interactions among virus, prokaryotic host and the environment in mangrove wetlands from multiple perspectives, including viral lifestyles, virus-host interactions, and habitat dependence. Importantly, it provides a new ecological perspective on how mangrove viruses are adapted to the stress posed by urbanization.

Symbiotic virus-bacteria interactions in biological treatment of coking wastewater manipulating bacterial physiological activities

Biological treatment is commonly used in coking wastewater (CWW) treatment. Prokaryotic microbial communities in CWW treatment have been comprehensively studied. However, viruses, as the critical microorganisms affecting microbial processes and thus engineering parameters, still remain poorly understood in CWW treatment context. Employing viromics sequencing, the composition and function of the viral community in CWW treatment were discovered, revealing novel viral communities and key auxiliary metabolic functions. Caudovirales appeared to be the predominant viral order in the oxic-hydrolytic-oxic (OHO) CWW treatment combination, showing relative abundances of 62.47 %, 56.64 % and 92.20 % in bioreactors O1, H and O2, respectively. At the family level, Myoviridae, Podoviridae and Siphoviridae mainly prevailed in bioreactors O1 and H while Phycodnaviridae dominated in O2. A total of 56.23-92.24% of novel viral contigs defied family-level characterization in this distinct CWW habitat. The virus-host prediction results revealed most viruses infecting the specific functional taxa Pseudomonas, Acidovorax and Thauera in the entire OHO combination, demonstrating the viruses affecting bacterial physiology and pollutants removal from CWW. Viral auxiliary metabolic genes (AMGs) were screened, revealing their involvement in the metabolism of contaminants and toxicity tolerance. In the bioreactor O1, AMGs were enriched in detoxification and phosphorus ingestion, where glutathione S-transferase (GSTs) and beta-ketoadipyl CoA thiolase (fadA) participated in biodegradation of polycyclic aromatic hydrocarbons and phenols, respectively. In the bioreactors H and O2, the AMGs focused on cell division and epicyte formation of the hosts, where GDPmannose 4,6-dehydratase (gmd) related to lipopolysaccharides biosynthesis was considered to play an important role in the growth of nitrifiers. The diversities of viruses and AMGs decreased along the CWW treatment process, pointing to a reinforced virus-host adaptive strategy in stressful operation environments. In this study, the symbiotic virus-bacteria interaction patterns were proposed with a theoretical basis for promoting CWW biological treatment efficiency. The findings filled the gaps in the virus-bacteria interactions at the full-scale CWW treatment and provided great value for understanding the mechanism of biological toxicity and sludge activity in industrial wastewater treatment.

Enrichable consortia of microbial symbionts degrade macroalgal polysaccharides in Kyphosus fish

Coastal herbivorous fishes consume macroalgae, which is then degraded by microbes along their digestive tract. However, there is scarce genomic information about the microbiota that perform this degradation. This study explores the potential of Kyphosus gastrointestinal microbial symbionts to collaboratively degrade and ferment polysaccharides from red, green, and brown macroalgae through in silico study of carbohydrate-active enzyme and sulfatase sequences. Recovery of metagenome-assembled genomes (MAGs) from previously described Kyphosus gut metagenomes and newly sequenced bioreactor enrichments reveals differences in enzymatic capabilities between the major microbial taxa in Kyphosus guts. The most versatile of the recovered MAGs were from the Bacteroidota phylum, whose MAGs house enzyme collections able to decompose a variety of algal polysaccharides. Unique enzymes and predicted degradative capacities of genomes from the Bacillota (genus Vallitalea) and Verrucomicrobiota (order Kiritimatiellales) highlight the importance of metabolic contributions from multiple phyla to broaden polysaccharide degradation capabilities. Few genomes contain the required enzymes to fully degrade any complex sulfated algal polysaccharide alone. The distribution of suitable enzymes between MAGs originating from different taxa, along with the widespread detection of signal peptides in candidate enzymes, is consistent with cooperative extracellular degradation of these carbohydrates. This study leverages genomic evidence to reveal an untapped diversity at the enzyme and strain level among Kyphosus symbionts and their contributions to macroalgae decomposition. Bioreactor enrichments provide a genomic foundation for degradative and fermentative processes central to translating the knowledge gained from this system to the aquaculture and bioenergy sectors.IMPORTANCESeaweed has long been considered a promising source of sustainable biomass for bioenergy and aquaculture feed, but scalable industrial methods for decomposing terrestrial compounds can struggle to break down seaweed polysaccharides efficiently due to their unique sulfated structures. Fish of the genus Kyphosus feed on seaweed by leveraging gastrointestinal bacteria to degrade algal polysaccharides into simple sugars. This study reconstructs metagenome-assembled genomes for these gastrointestinal bacteria to enhance our understanding of herbivorous fish digestion and fermentation of algal sugars. Investigations at the gene level identify Kyphosus guts as an untapped source of seaweed-degrading enzymes ripe for further characterization. These discoveries set the stage for future work incorporating marine enzymes and microbial communities in the industrial degradation of algal polysaccharides.

Insights into the phage community structure and potential function in silage fermentation

The virus that infects bacteria known as phage, plays a crucial role in the biogeochemical cycling of nutrients. However, the community structure and potential functions of phages in silage fermentation remain largely unexplored. In this study, we utilized viral metagenomics (viromics) to investigate the types, lifestyles, functions, and nutrient utilization patterns of phages in silage. Our findings indicated a high prevalence of annotated phages belonging to Caudovirales and Geplafuvirales, as well as unclassified phages in silage. The predominant host types for these phages were Campylobacterales and Enterobacterales. Virulent phages dominated the silage environment due to their broader range of hosts and enhanced survival capabilities. All identified phages present in silage were found to be non-pathogenic. Although temperate and virulent phages carried distinct genes associated with nutrient cycling processes, the shared genes (prsA) involved in carbon metabolism underscore the potential significance of phages in regulating carbon metabolism in silage. Overall, our findings provide a valuable foundation for further exploring the complex interactions between phages and microorganisms in regulating silage fermentation quality.

Short-, long-read metagenome and virome reveal the profile of phage-mediated ARGs in anoxic-oxic processes for swine wastewater treatment

Phages are among the most widely spread viruses, but their profiles and the antibiotic resistance genes (ARGs) they carry in swine wastewater remain underexplored. The present study investigated the distribution characteristics of phages and their ARG risk in anoxic/oxic (A/O) wastewater treatment processes of swine farms using short- and long-read metagenome and virome. The results demonstrated that the virome could extract more phage sequences than the total metagenome; thus, it was more suited for studying phages in wastewater settings. Intriguingly, phages had significantly lower abundance of ARG than ARGs harbored by total microorganisms (P < 0.01). Eleven ARGs co-occurred with phages and bacteria (R > 0.6 and P < 0.05), with Siphoviridae being the phage co-occurring with the most ARGs (5). Horizontal gene transfer (HGT) events were observed between Proteobacteria and the major phyla except for Bacteroidota. Furthermore, there were prophage sequences and ARGs on the same contig in bacterial MAGs. These data strongly demonstrate that phages promote horizontal transfer of ARG between bacterial hosts in A/O processes for swine wastewater treatment. Therefore, the risk of phage-mediated horizontal transfer of ARGs cannot be overlooked despite the low abundance of phage ARGs (pARG).

Airborne antibiotic resistome and microbiome in pharmaceutical factories

Antimicrobial resistance is considered to be one of the biggest public health problems, and airborne transmission is an important but under-appreciated pathway for the spread of antibiotic resistance genes (ARGs) in the environment. Previous research has shown pharmaceutical factories to be a major source of ARGs and antibiotic resistant bacteria (ARB) in the surrounding receiving water and soil environments. Pharmaceutical factories are hotspots of antibiotic resistance, but the atmospheric transmission and its environmental risk remain more concerns. Here, we conducted a metagenomic investigation into the airborne microbiome and resistome in three pharmaceutical factories in China. Soil (average: 38.45%) and wastewater (average: 28.53%) were major contributors of airborne resistome. ARGs (vanR/vanS, blaOXA, and CfxA) conferring resistance to critically important clinically used antibiotics were identified in the air samples. The wastewater treatment area had significantly higher relative abundances of ARGs (average: 0.64 copies/16S rRNA). Approximately 28.2% of the detected airborne ARGs were found to be associated with plasmids, and this increased to about 50% in the wastewater treatment area. We have compiled a list of high-risk airborne ARGs found in pharmaceutical factories. Moreover, A total of 1,043 viral operational taxonomic units were identified and linked to 47 family-group taxa. Different CRISPR-Cas immune systems have been identified in bacterial hosts in response to phage infection. Similarly, higher phage abundance (average: 2451.70 PPM) was found in the air of the wastewater treatment area. Our data provide insights into the antibiotic resistance gene profiles and microbiome (bacterial and non-bacterial) in pharmaceutical factories and reveal the potential role of horizontal transfer in the spread of airborne ARGs, with implications for human and animal health.

Correlation between the gut microbiome and neurodegenerative diseases: a review of metagenomics evidence

A growing body of evidence suggests that the gut microbiota contributes to the development of neurodegenerative diseases via the microbiota-gut-brain axis. As a contributing factor, microbiota dysbiosis always occurs in pathological changes of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. High-throughput sequencing technology has helped to reveal that the bidirectional communication between the central nervous system and the enteric nervous system is facilitated by the microbiota's diverse microorganisms, and for both neuroimmune and neuroendocrine systems. Here, we summarize the bioinformatics analysis and wet-biology validation for the gut metagenomics in neurodegenerative diseases, with an emphasis on multi-omics studies and the gut virome. The pathogen-associated signaling biomarkers for identifying brain disorders and potential therapeutic targets are also elucidated. Finally, we discuss the role of diet, prebiotics, probiotics, postbiotics and exercise interventions in remodeling the microbiome and reducing the symptoms of neurodegenerative diseases.

COBRA improves the completeness and contiguity of viral genomes assembled from metagenomes

Viruses are often studied using metagenome-assembled sequences, but genome incompleteness hampers comprehensive and accurate analyses. Contig Overlap Based Re-Assembly (COBRA) resolves assembly breakpoints based on the de Bruijn graph and joins contigs. Here we benchmarked COBRA using ocean and soil viral datasets. COBRA accurately joined the assembled sequences and achieved notably higher genome accuracy than binning tools. From 231 published freshwater metagenomes, we obtained 7,334 bacteriophage clusters, ~83% of which represent new phage species. Notably, ~70% of these were circular, compared with 34% before COBRA analyses. We expanded sampling of huge phages (≥200 kbp), the largest of which was curated to completion (717 kbp). Improved phage genomes from Rotsee Lake provided context for metatranscriptomic data and indicated the in situ activity of huge phages, whiB-encoding phages and cysC- and cysH-encoding phages. COBRA improves viral genome assembly contiguity and completeness, thus the accuracy and reliability of analyses of gene content, diversity and evolution.

Large language models improve annotation of prokaryotic viral proteins

Viral genomes are poorly annotated in metagenomic samples, representing an obstacle to understanding viral diversity and function. Current annotation approaches rely on alignment-based sequence homology methods, which are limited by the paucity of characterized viral proteins and divergence among viral sequences. Here we show that protein language models can capture prokaryotic viral protein function, enabling new portions of viral sequence space to be assigned biologically meaningful labels. When applied to global ocean virome data, our classifier expanded the annotated fraction of viral protein families by 29%. Among previously unannotated sequences, we highlight the identification of an integrase defining a mobile element in marine picocyanobacteria and a capsid protein that anchors globally widespread viral elements. Furthermore, improved high-level functional annotation provides a means to characterize similarities in genomic organization among diverse viral sequences. Protein language models thus enhance remote homology detection of viral proteins, serving as a useful complement to existing approaches.

Investigating the viral ecology and contribution to the microbial ecology in full-scale mesophilic anaerobic digesters

In an attempt to assess the diversity of viruses and their potential to modulate the metabolism of functional microorganisms in anaerobic digesters, we collected digestate from three mesophilic anaerobic digesters in full-scale wastewater treatment plants treating real municipal wastewater. The reads were analyzed using bioinformatics algorithms to elucidate viral diversity, identify their potential role in modulating the metabolism of functional microorganisms, and provide essential genomic information for the potential use of virus-mediated treatment in controlling the anaerobic digester microbiome. We found that Siphoviridae was the dominant family in mesophilic anaerobic digesters, followed by Myoviridae and Podoviridae. Lysogeny was prevalent in mesophilic anaerobic digesters as the majority of metagenome-assembled genomes contained at least one viral genome within them. One virus within the genome of an acetoclastic methanogen (Methanothrix soehngenii) was observed with a gene (fwdE) acquired via lateral transfer from hydrogenotrophic methanogens. The virus-mediated acquisition of fwdE gene enables possibility of mixotrophic methanogenesis in Methanothrix soehngenii. This evidence highlighted that lysogeny provides fitness advantage to methanogens in anaerobic digesters by adding flexibility to changing substrates. Similarly, we found auxiliary metabolic genes, such as cellulase and alpha glucosidase, of bacterial origin responsible for sludge hydrolysis in viruses. Additionally, we discovered novel viral genomes and provided genomic information on viruses infecting acidogenic, acetogenic, and pathogenic bacteria that can potentially be used for virus-mediated treatment to deal with the souring problem in anaerobic digesters and remove pathogens from biosolids before land application. Collectively, our study provides a genome-level understanding of virome in conjunction with the microbiome in anaerobic digesters that can be used to optimize the anaerobic digestion process for efficient biogas generation.

Computational host range prediction-The good, the bad, and the ugly

The rapid emergence and spread of antimicrobial resistance across the globe have prompted the usage of bacteriophages (i.e. viruses that infect bacteria) in a variety of applications ranging from agriculture to biotechnology and medicine. In order to effectively guide the application of bacteriophages in these multifaceted areas, information about their host ranges-that is the bacterial strains or species that a bacteriophage can successfully infect and kill-is essential. Utilizing sixteen broad-spectrum (polyvalent) bacteriophages with experimentally validated host ranges, we here benchmark the performance of eleven recently developed computational host range prediction tools that provide a promising and highly scalable supplement to traditional, but laborious, experimental procedures. We show that machine- and deep-learning approaches offer the highest levels of accuracy and precision-however, their predominant predictions at the species- or genus-level render them ill-suited for applications outside of an ecosystems metagenomics framework. In contrast, only moderate sensitivity (<80 per cent) could be reached at the strain-level, albeit at low levels of precision (<40 per cent). Taken together, these limitations demonstrate that there remains room for improvement in the active scientific field of in silico host prediction to combat the challenge of guiding experimental designs to identify the most promising bacteriophage candidates for any given application.

Enrichable consortia of microbial symbionts degrade macroalgal polysaccharides in Kyphosus fish

Coastal herbivorous fishes consume macroalgae, which is then degraded by microbes along their digestive tract. However, there is scarce foundational genomic work on the microbiota that perform this degradation. This study explores the potential of Kyphosus gastrointestinal microbial symbionts to collaboratively degrade and ferment polysaccharides from red, green, and brown macroalgae through in silico study of carbohydrate-active enzyme and sulfatase sequences. Recovery of metagenome-assembled genomes (MAGs) reveals differences in enzymatic capabilities between the major microbial taxa in Kyphosus guts. The most versatile of the recovered MAGs were from the Bacteroidota phylum, whose MAGs house enzymes able to decompose a variety of algal polysaccharides. Unique enzymes and predicted degradative capacities of genomes from the Bacillota (genus Vallitalea) and Verrucomicrobiota (order Kiritimatiellales) suggest the potential for microbial transfer between marine sediment and Kyphosus digestive tracts. Few genomes contain the required enzymes to fully degrade any complex sulfated algal polysaccharide alone. The distribution of suitable enzymes between MAGs originating from different taxa, along with the widespread detection of signal peptides in candidate enzymes, is consistent with cooperative extracellular degradation of these carbohydrates. This study leverages genomic evidence to reveal an untapped diversity at the enzyme and strain level among Kyphosus symbionts and their contributions to macroalgae decomposition. Bioreactor enrichments provide a genomic foundation for degradative and fermentative processes central to translating the knowledge gained from this system to the aquaculture and bioenergy sectors.

Hi-C metagenome sequencing reveals soil phage-host interactions

Bacteriophages are abundant in soils. However, the majority are uncharacterized, and their hosts are unknown. Here, we apply high-throughput chromosome conformation capture (Hi-C) to directly capture phage-host relationships. Some hosts have high centralities in bacterial community co-occurrence networks, suggesting phage infections have an important impact on the soil bacterial community interactions. We observe increased average viral copies per host (VPH) and decreased viral transcriptional activity following a two-week soil-drying incubation, indicating an increase in lysogenic infections. Soil drying also alters the observed phage host range. A significant negative correlation between VPH and host abundance prior to drying indicates more lytic infections result in more host death and inversely influence host abundance. This study provides empirical evidence of phage-mediated bacterial population dynamics in soil by directly capturing specific phage-host interactions.

Viral Diversity in Benthic Abyssal Ecosystems: Ecological and Methodological Considerations

Viruses are the most abundant 'biological entities' in the world's oceans. However, technical and methodological constraints limit our understanding of their diversity, particularly in benthic abyssal ecosystems (>4000 m depth). To verify advantages and limitations of analyzing virome DNA subjected either to random amplification or unamplified, we applied shotgun sequencing-by-synthesis to two sample pairs obtained from benthic abyssal sites located in the North-eastern Atlantic Ocean at ca. 4700 m depth. One amplified DNA sample was also subjected to single-molecule long-read sequencing for comparative purposes. Overall, we identified 24,828 viral Operational Taxonomic Units (vOTUs), belonging to 22 viral families. Viral reads were more abundant in the amplified DNA samples (38.5-49.9%) compared to the unamplified ones (4.4-5.8%), with the latter showing a greater viral diversity and 11-16% of dsDNA viruses almost undetectable in the amplified samples. From a procedural point of view, the viromes obtained by direct sequencing (without amplification step) provided a broader overview of both ss and dsDNA viral diversity. Nevertheless, our results suggest that the contextual use of random amplification of the same sample and long-read technology can improve the assessment of viral assemblages by reducing off-target reads.

Depth-driven patterns in lytic viral diversity, auxiliary metabolic gene content, and productivity in offshore oligotrophic waters

Introduction

Marine viruses regulate microbial population dynamics and biogeochemical cycling in the oceans. The ability of viruses to manipulate hosts' metabolism through the expression of viral auxiliary metabolic genes (AMGs) was recently highlighted, having important implications in energy production and flow in various aquatic environments. Up to now, the presence and diversity of viral AMGs is studied using -omics data, and rarely using quantitative measures of viral activity alongside.

Methods

In the present study, four depth layers (5, 50, 75, and 1,000 m) with discrete hydrographic features were sampled in the Eastern Mediterranean Sea; we studied lytic viral community composition and AMG content through metagenomics, and lytic production rates through the viral reduction approach in the ultra-oligotrophic Levantine basin where knowledge regarding viral actions is rather limited.

Results and Discussion

Our results demonstrate depth-dependent patterns in viral diversity and AMG content, related to differences in temperature, nutrients availability, and host bacterial productivity and abundance. Although lytic viral production rates were similar along the water column, the virus-to-bacteria ratio was higher and the particular set of AMGs was more diverse in the bathypelagic (1,000 m) than the shallow epipelagic (5, 50, and 75 m) layers, revealing that the quantitative effect of viruses on their hosts may be the same along the water column through the intervention of different AMGs. In the resource- and energy-limited bathypelagic waters of the Eastern Mediterranean, the detected AMGs could divert hosts' metabolism toward energy production, through a boost in gluconeogenesis, fatty-acid and glycan biosynthesis and metabolism, and sulfur relay. Near the deep-chlorophyll maximum depth, an exceptionally high percentage of AMGs related to photosynthesis was noticed. Taken together our findings suggest that the roles of viruses in the deep sea might be even more important than previously thought as they seem to orchestrate energy acquisition and microbial community dynamics, and thus, biogeochemical turnover in the oceans.

Diversity and function of mountain and polar supraglacial DNA viruses

Mountain and polar glaciers cover 10% of the Earth's surface and are typically extreme environments that challenge life of all forms. Viruses are abundant and active in supraglacial ecosystems and play a crucial role in controlling the supraglacial microbial communities. However, our understanding of virus ecology on glacier surfaces and their potential impacts on downstream ecosystems remains limited. Here, we present the supraglacial virus genome (SgVG) catalog, a 15-fold expanded genomic inventory of 10,840 DNA-virus species from 38 mountain and polar glaciers, spanning habitats such as snow, ice, meltwater, and cryoconite. Supraglacial DNA-viruses were highly specific compared to viruses in other ecosystems yet exhibited low public health risks. Supraglacial viral communities were primarily constrained by habitat, with cryoconite displaying the highest viral activity levels. We observed a prevalence of lytic viruses in all habitats, especially in cryoconite, but a high level of lysogenic viruses in snow and ice. Additionally, we found that supraglacial viruses could be linked to ∼83% of obtained prokaryotic phyla/classes and possessed the genetic potential to promote metabolism and increase cold adaptation, cell mobility, and phenolic carbon use of hosts in hostile environmental conditions using diverse auxiliary metabolic genes. Our results provide the first systematic characterization of the diversity, function, and public health risks evaluation of mountain and polar supraglacial DNA viruses. This understanding of glacial viruses is crucial for function assessments and ecological modeling of glacier ecosystems, especially for the Tibetan Plateau's Mountain glaciers, which support ∼20% of the human populations on Earth.

Global diversity and biogeography of DNA viral communities in activated sludge systems

BACKGROUND

Activated sludge (AS) systems in wastewater treatment plants (WWTPs) harbor enormous viruses that regulate microbial metabolism and nutrient cycling, significantly influencing the stability of AS systems. However, our knowledge about the diversity of viral taxonomic groups and functional traits in global AS systems is still limited. To address this gap, we investigated the global diversity and biogeography of DNA viral communities in AS systems using 85,114 viral operational taxonomic units (vOTUs) recovered from 144 AS samples collected across 54 WWTPs from 13 different countries.

RESULTS

AS viral communities and their functional traits exhibited distance-decay relationship (DDR) at the global scale and latitudinal diversity gradient (LDG) from equator to mid-latitude. Furthermore, it was observed that AS viral community and functional gene structures were largely driven by the geographic factors and wastewater types, of which the geographic factors were more important. Carrying and disseminating auxiliary metabolic genes (AMGs) associated with the degradation of polysaccharides, sulfate reduction, denitrification, and organic phosphoester hydrolysis, as well as the lysis of crucial functional microbes that govern biogeochemical cycles were two major ways by which viruses could regulate AS functions. It was worth noting that our study revealed a high abundance of antibiotic resistance genes (ARGs) in viral genomes, suggesting that viruses were key reservoirs of ARGs in AS systems.

CONCLUSIONS

Our results demonstrated the highly diverse taxonomic groups and functional traits of viruses in AS systems. Viral lysis of host microbes and virus-mediated HGT can regulate the biogeochemical and nutrient cycles, thus affecting the performance of AS systems. These findings provide important insights into the viral diversity, function, and ecology in AS systems on a global scale. Video Abstract.

Metagenomic analysis unveils the underexplored roles of prokaryotic viruses in a full-scale landfill leachate treatment plant

Enormous viral populations have been identified in activated sludge systems, but their ecological and biochemical roles in landfill leachate treatment plants remain poorly understood. To address this knowledge gap, we conducted an in-depth analysis using 36 metagenomic datasets that we collected and sequenced during a half-year time-series sampling campaign at six sites in a full-scale landfill leachate treatment plant (LLTP), elucidating viral distribution, virus‒host dynamics, virus-encoded auxiliary metabolic genes (AMGs), and viral contributions to the spread of virulence and antibiotic resistance genes. Our findings demonstrated that viral and prokaryotic communities differed widely among different treatment units, with stability over time. LLTP viruses were linked to various prokaryotic hosts, spanning 35 bacterial phyla and one archaeal phylum, which included the core microbes involved in biological treatments, as well as some of the less well-characterized microbial dark matter phyla. By encoding 2364 auxiliary metabolic genes (AMGs), viruses harbored the potential to regulate microbial nucleotide metabolism, facilitate the biodegradation of complex organic matter, and enhance flocculation and settling in biological treatment plants. The abundance distribution of AMGs varied considerably across treatment units and showed a lifestyle-dependent pattern with temperate virus-associated AMGs exhibiting a higher average abundance in downstream biological treatment units and effluent water. Meanwhile, temperate viruses tended to carry a higher load of virulence factor genes (VFGs), antibiotic resistance genes (ARGs), and biotic and metal resistance genes (BMRGs), and engaged in more frequent gene exchanges with prokaryotes than lytic viruses, thus acting as a pivotal contributor to the dissemination of pathogenicity and resistance genes in downstream LLTP units. This study provided a comprehensive profile of viral and prokaryotic communities in the LLTP and unveiled the varying roles of different-lifestyle viruses in biochemical processes and water quality safety.

Combined virome analysis and metagenomic sequencing to reveal the viral communities and risk of virus-associated antibiotic resistance genes during composting

The issue of antibiotic resistance genes (ARGs) pollution in manure has garnered significant attention, with viruses now being recognized as crucial carriers and disseminators of ARGs. However, the virus-associated ARG profiles and potential health risks in composts are still unclear. In this study, the viral communities and associated ARGs in biogas residue and pig faeces composts were profiled by virome analysis. The viral communities were dominated by Caudovirales, and non-thermophilic viruses were inactivated during composting. The diversity and abundance of ARGs were lower in virome than in metagenome, while ARGs' risk was greater in virome than in metagenome. There were six bacterial genera identified as viral hosts at the genomic level, Pseudomonas and Clostridium carried high-risk ARGs. Virus-associated ARGs in viral hosts had a higher risk rank than non-virus-associated ARGs. Composting reduced the diversity, abundance and risk of viral ARGs. The risk of ARGs in biogas residues was significantly lower than that of pig faeces in the initial period of composting, and the two different substracts equally less harmful after composting. These results revealed that viruses play a non-negligible role in spreading ARGs, posing high risk to environmental and human health.

Metagenome-derived virus-microbe ratios across ecosystems

It is generally assumed that viruses outnumber cells on Earth by at least tenfold. Virus-to-microbe ratios (VMR) are largely based on counts of fluorescently labelled virus-like particles. However, these exclude intracellular viruses and potentially include false positives (DNA-containing vesicles, gene-transfer agents, unspecifically stained inert particles). Here, we develop a metagenome-based VMR estimate (mVRM) that accounts for DNA viruses across all stages of their replication cycles (virion, intracellular lytic and lysogenic) by using normalised RPKM (reads per kilobase of gene sequence per million of mapped metagenome reads) counts of the major capsid protein (MCP) genes and cellular universal single-copy genes (USCGs) as proxies for virus and cell counts, respectively. After benchmarking this strategy using mock metagenomes with increasing VMR, we inferred mVMR across different biomes. To properly estimate mVMR in aquatic ecosystems, we generated metagenomes from co-occurring cellular and viral fractions (>50 kDa-200 µm size-range) in freshwater, seawater and solar saltern ponds (10 metagenomes, 2 control metaviromes). Viruses outnumbered cells in freshwater by ~13 fold and in plankton from marine and saline waters by ~2-4 fold. However, across an additional set of 121 diverse non-aquatic metagenomes including microbial mats, microbialites, soils, freshwater and marine sediments and metazoan-associated microbiomes, viruses, on average, outnumbered cells by barely two-fold. Although viruses likely are the most diverse biological entities on Earth, their global numbers might be closer to those of cells than previously estimated.

PhaGenus: genus-level classification of bacteriophages using a Transformer model

MOTIVATION

Bacteriophages (phages for short), which prey on and replicate within bacterial cells, have a significant role in modulating microbial communities and hold potential applications in treating antibiotic resistance. The advancement of high-throughput sequencing technology contributes to the discovery of phages tremendously. However, the taxonomic classification of assembled phage contigs still faces several challenges, including high genetic diversity, lack of a stable taxonomy system and limited knowledge of phage annotations. Despite extensive efforts, existing tools have not yet achieved an optimal balance between prediction rate and accuracy.

RESULTS

In this work, we develop a learning-based model named PhaGenus, which conducts genus-level taxonomic classification for phage contigs. PhaGenus utilizes a powerful Transformer model to learn the association between protein clusters and support the classification of up to 508 genera. We tested PhaGenus on four datasets in different scenarios. The experimental results show that PhaGenus outperforms state-of-the-art methods in predicting low-similarity datasets, achieving an improvement of at least 13.7%. Additionally, PhaGenus is highly effective at identifying previously uncharacterized genera that are not represented in reference databases, with an improvement of 8.52%. The analysis of the infants' gut and GOV2.0 dataset demonstrates that PhaGenus can be used to classify more contigs with higher accuracy.

Comparative analysis of gut DNA viromes in wild and captive Himalayan vultures

Introduction

Himalayan vultures (Gyps hinalayensis) are widely distributed on the Qinghai-Tibetan Plateau and play a crucial role in maintaining the ecological balance by feeding on decayed corpses of wild and domestic animals. Large-scale culture and metagenomics studies have broadened our understanding of viral diversity in animals' gastrointestinal tracts. However, despite the importance of gut viral communities in regulating bacterial diversity and performing symbiotic functions, no gut viral study has been conducted on Himalayan vultures. Furthermore, the impact of captivity on the gut virome of these vultures remains unknown.

Methods

In this study, metagenomic sequencing methods targeting DNA of virus-like particles enriched from feces were used to characterize the gut DNA viromes of wild and captive Himalayan vultures.

Results

In total, 22,938 unique viral operational taxonomic units (vOTUs) were identified and assigned to 140 viral genera in 41 viral families. These families included viruses associated with bacteria, animals, plants, insects, and archaea. Phage communities, including Siphoviridae, Microviridae, Myoviridae, Inoviridae, and Herelleviridae, dominated the gut virome of Himalayan vultures. Wild vultures exhibited higher viral richness and diversity compared with those in captivity. The functional capacity of the gut virome was characterized by identifying 93 KEGG pathways, which were significantly enriched in metabolism and genetic information processing. Abundant auxiliary metabolic genes, such as carbohydrate-active enzyme, and antibiotic resistance genes, were also found in the vultures' gut virome.

Discussion

Our findings reveal the complex and diverse viral community present in the gut virome of Himalayan vultures, which varies between wild, and captive states. The DNA virome dataset establishes a baseline for the vultures' gut virome and will serve as a reference for future virus isolation and cultivation. Understanding the impact of captivity on the gut virome contributes to our knowledge of vultures' response to captivity and aids in optimizing their rehabilitation and implementing protective measures.

Viral community structure and functional potential vary with lifestyle and altitude in soils of Mt. Everest

More and more focus has been placed on the processes by which viruses interact with bacteria to influence the biogeochemical cycles. The intricacy of soil matrix and the incompleteness of databases, however, constrains the investigation on the mechanisms of soil viruses exerting ecological functions. The modification of ICTV classification system in 2021 was also a huge shock to the results of the existing studies on virome. We used viral metagenomes combined with soil properties to investigate the viral community composition and auxiliary metabolic genes (AMGs) profiles of various lifestyles in soils of Mount Everest at different altitudes. Viral lifestyles and soil nutrient levels were found to significantly influence the diversity and composition of viral communities. Temperate virus lifestyle dominated in high-altitude soils with lower level of nutrients because of its stronger survival adaptability, and the structural and functional diversity of viral communities was positively correlated with the contents of nutrients (total carbon and total nitrogen). The primary types of AMGs carried by temperate and virulent viruses differed, while a variety of genes involved in carbon metabolism highlighted the potential importance of viruses in the soil carbon cycle of Mount Everest. Moreover, the abundance of AMGs encoding carbohydrate-active enzymes had a significant and positive correlation with soil C/N ratio. Overall, these findings provide a context for further exploration on the regulatory mechanisms of viruses in carbon cycle via interactions with microorganisms.

Virome reveals effect of Ulva prolifera green tide on the structural and functional profiles of virus communities in coastal environments

Viruses are widely distributed in marine environments, where they influence the transformation of matter and energy by modulating host metabolism. Driven by eutrophication, green tides are a rising concern in Chinese coastal areas, and are a serious ecological disaster that negatively affects coastal ecosystems and disrupts biogeochemical cycles. Although the composition of bacterial communities in green algae has been investigated, the diversity and roles of viruses in green algal blooms are largely unexplored. Therefore, the diversity, abundance, lifestyle, and metabolic potential of viruses in a natural bloom in Qingdao coastal area were investigated at three different stages (pre-bloom, during-bloom, and post-bloom) by metagenomics analysis. The dsDNA viruses, Siphoviridae, Myoviridae, Podoviridae, and Phycodnaviridae, were found to dominate the viral community. The viral dynamics exhibited distinct temporal patterns across different stages. The composition of the viral community varied during the bloom, especially in populations with low abundance. The lytic cycle was most predominant, and the abundance of lytic viruses increased slightly in the post-bloom stage. The diversity and richness of the viral communities varied distinctly during the green tide, and the post-bloom stage favored viral diversity and richness. The total organic carbon, dissolved oxygen, NO^3-, NO^2-, PO₄^3-, chlorophyll-a contents, and temperature variably co-influenced the viral communities. The primary hosts included bacteria, algae, and other microplankton. Network analysis revealed the closer links between the viral communities as the bloom progressed. Functional prediction revealed that the viruses possibly influenced the biodegradation of microbial hydrocarbons and carbon by metabolic augmentation via auxiliary metabolic genes. The composition, structure, metabolic potential, and interaction taxonomy of the viromes differed significantly across the different stages of the green tide. The study demonstrated that the ecological event shaped the viral communities during algal bloom, and the viral communities played a significant role in phycospheric microecology.

Longitudinal Investigation of Enteric Virome Signatures from Parental-Generation to Offspring Pigs

To date, studies on the swine gut microbiome have focused almost exclusively on bacteria. Despite recent advances in the understanding of the swine gut bacteriome at different growth stages, a comprehensive longitudinal study of the lifetime dynamics of the swine gut virome is lacking. Here, we used metagenomic sequencing combined with bioinformatic analysis techniques to characterize the gut viromes of parental-generation and offspring pigs at different biological classification levels. We collected 54 fecal samples from 36 parental-generation pigs (18 breeding boars [Duroc] and 18 pregnant/lactating sows [Landrace]) and 108 fecal samples from 18 offspring pigs during the lactation (day 3), nursery (days 26, 35, and 49), growing (day 120), and finishing (day 180) stages. Alpha diversity, including community richness (richness index) and diversity (Shannon index), showed an overall increasing trend in offspring pigs. Distinct shifts (beta diversity) in the microbiome structure along different growth stages were observed. The linear discriminant analysis effect size (LEfSe) algorithm revealed 53 viral genus that are stage specific. Host prediction results showed that enteric viruses are probably correlated with carbohydrate decomposition. We identified abundant auxiliary carbohydrate-active enzyme (CAZyme) genes from enteric viruses, most of which are glycoside hydrolase genes and participate in the biolysis of complex polysaccharides. IMPORTANCE This study shows that distinct stage-associated swine gut viromes may be determined by age and/or gut physiology at different growth stages, and enteric viruses probably manipulate carbohydrate decomposition by abundant glycoside hydrolases. These findings fill a gap in the longitudinal pattern of the swine gut virome and lay the foundation for research on the function of swine enteric viruses.

Water mass age structures the auxiliary metabolic gene content of free-living and particle-attached deep ocean viral communities

BACKGROUND

Viruses play important roles in the ocean's biogeochemical cycles. Yet, deep ocean viruses are one of the most under-explored fractions of the global biosphere. Little is known about the environmental factors that control the composition and functioning of their communities or how they interact with their free-living or particle-attached microbial hosts.

RESULTS

We analysed 58 viral communities associated with size-fractionated free-living (0.2-0.8 μm) and particle-attached (0.8-20 μm) cellular metagenomes from bathypelagic (2150-4018 m deep) microbiomes obtained during the Malaspina expedition. These metagenomes yielded 6631 viral sequences, 91% of which were novel, and 67 represented high-quality genomes. Taxonomic classification assigned 53% of the viral sequences to families of tailed viruses from the order Caudovirales. Computational host prediction associated 886 viral sequences to dominant members of the deep ocean microbiome, such as Alphaproteobacteria (284), Gammaproteobacteria (241), SAR324 (23), Marinisomatota (39), and Chloroflexota (61). Free-living and particle-attached viral communities had markedly distinct taxonomic composition, host prevalence, and auxiliary metabolic gene content, which led to the discovery of novel viral-encoded metabolic genes involved in the folate and nucleotide metabolisms. Water mass age emerged as an important factor driving viral community composition. We postulated this was due to changes in quality and concentration of dissolved organic matter acting on the host communities, leading to an increase of viral auxiliary metabolic genes associated with energy metabolism among older water masses.

CONCLUSIONS

These results shed light on the mechanisms by which environmental gradients of deep ocean ecosystems structure the composition and functioning of free-living and particle-attached viral communities. Video Abstract.

Ecological drivers and potential functions of viral communities in flooded arsenic-contaminated paddy soils

This work revealed the profile of viral communities in paddy soils with different levels of arsenic (As) contamination during the flooded period. The structure of viral communities differed significantly in highly and moderately As-contaminated soils. The diversity of soil viral communities under high As contamination decreased. Siphoviridae, Podoviridae, Myoviridae, and Microviridae were the dominant viral families in all samples, and the relative abundances of five of the top 20 viral genera were significantly different between highly and moderately As-contaminated groups. Seventeen dissimilatory As(V)-reducing bacteria were predicted to host 161 viral operational taxonomic units (vOTUs), mainly affiliated with the genera of Sulfurospirillum, Deferribacter, Bacillus and Fusibacter. Among them, 28 vOTUs were also associated with Fe(III)-reducing bacteria, which belonged to different species of the genus Shewanella. Procrustes analysis showed that the community structure of soil viruses was strongly correlated with both prokaryotic community structure and geochemical properties. Random forest analyses revealed that the Total-Fe, DCB-Fe and oxalate-Fe were the most significant variables on viral community richness, while the total-As concentration was an important factor on the Shannon index. Furthermore, As resistance genes (ArsC, ArsR and ArsD), As methylation genes (arsM) and As transporter genes (Pst and Pit) were identified among the auxiliary metabolic genes (AMGs) of the virome. This work revealed that the viruses might influence microbial adaptation in response to As-induced stress, and provided a perspective on the potential virus-mediated biogeochemical cycling of As.

Lysogenic bacteriophages encoding arsenic resistance determinants promote bacterial community adaptation to arsenic toxicity

Emerging evidence from genomics gives us a glimpse into the potential contribution of lysogenic bacteriophages (phages) to the environmental adaptability of their hosts. However, it is challenging to quantify this kind of contribution due to the lack of appropriate genetic markers and the associated controllable environmental factors. Here, based on the unique transformable nature of arsenic (the controllable environmental factor), a series of flooding microcosms was established to investigate the contribution of arsM-bearing lysogenic phages to their hosts' adaptation to trivalent arsenic [As(III)] toxicity, where arsM is the marker gene associated with microbial As(III) detoxification. In the 15-day flooding period, the concentration of As(III) was significantly increased, and this elevated As(III) toxicity visibly inhibited the bacterial population, but the latter quickly adapted to As(III) toxicity. During the flooding period, some lysogenic phages re-infected new hosts after an early burst, while others persistently followed the productive cycle (i.e., lytic cycle). The unique phage-host interplay contributed to the rapid spread of arsM among soil microbiota, enabling the quick recovery of the bacterial community. Moreover, the higher abundance of arsM imparted a greater arsenic methylation capability to soil microbiota. Collectively, this study provides experimental evidence for lysogenic phages assisting their hosts in adapting to an extreme environment, which highlights the ecological perspectives on lysogenic phage-host mutualism.

Large language models improve annotation of viral proteins

Viral sequences are poorly annotated in environmental samples, a major roadblock to understanding how viruses influence microbial community structure. Current annotation approaches rely on alignment-based sequence ho-mology methods, which are limited by available viral sequences and sequence divergence in viral proteins. Here, we show that protein language model representations capture viral protein function beyond the limits of remote sequence homology by targeting two axes of viral sequence annotation: systematic labeling of protein families and function identification for biologic discovery. Protein language model representations capture protein functional properties specific to viruses and expand the annotated fraction of ocean virome viral protein sequences by 37%. Among unannotated viral protein families, we identify a novel DNA editing protein family that defines a new mobile element in marine picocyanobacteria. Protein language models thus significantly enhance remote homology detection of viral proteins and can be utilized to enable new biological discovery across diverse functional categories.

Children with autism show differences in the gut DNA virome compared to non-autistic children: a case control study

BACKGROUND

Several previous studies have identified a potential role that the gut microbiome can play in autism spectrum disorder (ASD) in children, but little is known about how variations in the virome may be involved in ASD. We aimed to understand the changes in the gut DNA virome of children with ASD.

METHODS

A case-control study was presented, in which 13 two-children families were observed while considering the age, mode of birth, history of antibiotic use, and vaccination history to minimize the influence of confounding factors. DNA viral metagenomic sequencing was successfully performed on stool samples from 11 children with ASD and 12 healthy non-ASD children. The basic composition and gene function of the participants' fecal DNA virome were detected and analyzed. Finally, the abundance and diversity of the DNA virome of children with ASD and their healthy siblings were compared.

RESULTS

The gut DNA virome in children aged 3-11 years was found to be dominated by the Siphoviridae family of Caudovirales. The proteins encoded by the DNA genes mainly carry out the functions of genetic information transmission and metabolism. Compared the gut DNA virome of ASD and healthy non-ASD children, their abundance of Caudovirales and Petitvirales both showed a significant negative correlation (r = -0.902, P < 0.01), there was no statistically significant difference in the relative abundance of viruses at the order and family levels, and a difference in the relative abundance at the genus level for Skunavirus (Ζ = -2.157, P = 0.031). Viral α diversity was reduced in children with ASD, but α diversity and β diversity did not differ statistically between groups.

CONCLUSIONS

This study indicates that elevated Skunavirus abundance and decreased α diversity in the gut DNA virulence group of children with ASD, but no statistically significant difference in the change in alpha and beta diversity. This provides preliminary cumulative information on virological aspects of the relationship between the microbiome and ASD, and should benefit future multi-omics and large sample studies on the gut microbes in children with ASD.

Metagenomic Sequencing Identified Specific Bacteriophage Signature Discriminating between Healthy and Diarrheal Neonatal Piglets

Neonatal diarrhea is one of the most severe diseases in human beings and pigs, leading to high mortality and growth faltering. Gut microbiome-related studies mostly focus on the relationship between bacteria and neonatal diarrhea onset, and no research study has investigated the role of the gut virome in neonatal diarrhea. Here, using metagenomic sequencing, we characterized the fecal viral community of diarrheal and healthy neonatal piglets. We found that the viral community of diarrheal piglets showed higher individual heterogeneity and elevated abundance of Myoviridae. By predicting the bacterial host of the identified viral genomes, phages infecting Proteobacteria, especially E. coli, were the dominant taxa in neonatal diarrheal piglets. Consistent with this, the antibiotic resistance gene of E. coli origin was also enriched in neonatal diarrheal piglets. Finally, we established a random forest model to accurately discriminate between neonatal diarrheal piglets and healthy controls and identified genus E. coli- and genus listeria-infecting bacteriophages, including psa and C5 viruses, as key biomarkers. In conclusion, we provide the first glance of viral community and function characteristics in diarrheal and healthy neonatal piglets. These findings expand our understanding of the relationship among phages, bacteria and diarrhea, and may facilitate the development of therapeutics for the prevention and treatment of neonatal diarrhea.

A Tale of Two Seasons: Distinct Seasonal Viral Communities in a Thermokarst Lake

Thermokarst lakes are important features of subarctic landscapes and are a substantial source of greenhouse gases, although the extent of gas produced varies seasonally. Microbial communities are responsible for the production of methane and CO₂ but the "top down" forces that influence microbial dynamics (i.e., grazers and viruses) and how they vary temporally within these lakes are still poorly understood. The aim of this study was to examine viral diversity over time to elucidate the seasonal structure of the viral communities in thermokarst lakes. We produced virus-enriched metagenomes from a subarctic peatland thermokarst lake in the summer and winter over three years. The vast majority of vOTUs assigned to viral families belonged to Caudovirales (Caudoviricetes), notably the morphological groups myovirus, siphovirus and podovirus. We identified two distinct communities: a dynamic, seasonal community in the oxygenated surface layer during the summer and a stable community found in the anoxic water layer at the bottom of the lake in summer and throughout much of the water column in winter. Comparison with other permafrost and northern lake metagenomes highlighted the distinct composition of viral communities in this permafrost thaw lake ecosystem.

Rhizosphere phage communities drive soil suppressiveness to bacterial wilt disease

BACKGROUND

Bacterial viruses, phages, play a key role in nutrient turnover and lysis of bacteria in terrestrial ecosystems. While phages are abundant in soils, their effects on plant pathogens and rhizosphere bacterial communities are poorly understood. Here, we used metagenomics and direct experiments to causally test if differences in rhizosphere phage communities could explain variation in soil suppressiveness and bacterial wilt plant disease outcomes by plant-pathogenic Ralstonia solanacearum bacterium. Specifically, we tested two hypotheses: (1) that healthy plants are associated with stronger top-down pathogen control by R. solanacearum-specific phages (i.e. 'primary phages') and (2) that 'secondary phages' that target pathogen-inhibiting bacteria play a stronger role in diseased plant rhizosphere microbiomes by indirectly 'helping' the pathogen.

RESULTS

Using a repeated sampling of tomato rhizosphere soil in the field, we show that healthy plants are associated with distinct phage communities that contain relatively higher abundances of R. solanacearum-specific phages that exert strong top-down pathogen density control. Moreover, 'secondary phages' that targeted pathogen-inhibiting bacteria were more abundant in the diseased plant microbiomes. The roles of R. solanacearum-specific and 'secondary phages' were directly validated in separate greenhouse experiments where we causally show that phages can reduce soil suppressiveness, both directly and indirectly, via top-down control of pathogen densities and by alleviating interference competition between pathogen-inhibiting bacteria and the pathogen.

CONCLUSIONS

Together, our findings demonstrate that soil suppressiveness, which is most often attributed to bacteria, could be driven by rhizosphere phage communities that regulate R. solanacearum densities and strength of interference competition with pathogen-suppressing bacteria. Rhizosphere phage communities are hence likely to be important in determining bacterial wilt disease outcomes and soil suppressiveness in agricultural fields. Video Abstract.

Advances in the field of phage-based therapy with special emphasis on computational resources

In the current era, one of the major challenges is to manage the treatment of drug/antibiotic-resistant strains of bacteria. Phage therapy, a century-old technique, may serve as an alternative to antibiotics in treating bacterial infections caused by drug-resistant strains of bacteria. In this review, a systematic attempt has been made to summarize phage-based therapy in depth. This review has been divided into the following two sections: general information and computer-aided phage therapy (CAPT). In the case of general information, we cover the history of phage therapy, the mechanism of action, the status of phage-based products (approved and clinical trials) and the challenges. This review emphasizes CAPT, where we have covered primary phage-associated resources, phage prediction methods and pipelines. This review covers a wide range of databases and resources, including viral genomes and proteins, phage receptors, host genomes of phages, phage-host interactions and lytic proteins. In the post-genomic era, identifying the most suitable phage for lysing a drug-resistant strain of bacterium is crucial for developing alternate treatments for drug-resistant bacteria and this remains a challenging problem. Thus, we compile all phage-associated prediction methods that include the prediction of phages for a bacterial strain, the host for a phage and the identification of interacting phage-host pairs. Most of these methods have been developed using machine learning and deep learning techniques. This review also discussed recent advances in the field of CAPT, where we briefly describe computational tools available for predicting phage virions, the life cycle of phages and prophage identification. Finally, we describe phage-based therapy's advantages, challenges and opportunities.

Virus classification for viral genomic fragments using PhaGCN2

Viruses are the most ubiquitous and diverse entities in the biome. Due to the rapid growth of newly identified viruses, there is an urgent need for accurate and comprehensive virus classification, particularly for novel viruses. Here, we present PhaGCN2, which can rapidly classify the taxonomy of viral sequences at the family level and supports the visualization of the associations of all families. We evaluate the performance of PhaGCN2 and compare it with the state-of-the-art virus classification tools, such as vConTACT2, CAT and VPF-Class, using the widely accepted metrics. The results show that PhaGCN2 largely improves the precision and recall of virus classification, increases the number of classifiable virus sequences in the Global Ocean Virome dataset (v2.0) by four times and classifies more than 90% of the Gut Phage Database. PhaGCN2 makes it possible to conduct high-throughput and automatic expansion of the database of the International Committee on Taxonomy of Viruses. The source code is freely available at https://github.com/KennthShang/PhaGCN2.0.

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.

Bioinformatics approaches for unveiling virus-host interactions

The coronavirus disease-2019 (COVID-19) pandemic has elucidated major limitations in the capacity of medical and research institutions to appropriately manage emerging infectious diseases. We can improve our understanding of infectious diseases by unveiling virus-host interactions through host range prediction and protein-protein interaction prediction. Although many algorithms have been developed to predict virus-host interactions, numerous issues remain to be solved, and the entire network remains veiled. In this review, we comprehensively surveyed algorithms used to predict virus-host interactions. We also discuss the current challenges, such as dataset biases toward highly pathogenic viruses, and the potential solutions. The complete prediction of virus-host interactions remains difficult; however, bioinformatics can contribute to progress in research on infectious diseases and human health.

Significant Differences in Planktonic Virus Communities Between "Cellular Fraction" (0.22 ~ 3.0 µm) and "Viral Fraction" (< 0.22 μm) in the Ocean

Compared to free-living viruses (< 0.22 m) in the ocean, planktonic viruses in the "cellular fraction" (0.22 ~ 3.0 μm) are now far less well understood, and the differences between them remain largely unexplored. Here, we revealed that even in the same seawater samples, the "cellular fraction" comprised significantly distinct virus communities from the free virioplankton, with only 13.87% overlap in viral contigs at the species level. Compared to the viral genomes deposited in NCBI RefSeq database, 99% of the assembled viral genomes in the "cellular fraction" represented novel genera. Notably, the assembled (near-) complete viral genomes within the "cellular fraction" were significantly larger than that in the "viral fraction," and the "cellular fraction" contained three times more species of giant viruses or jumbo phages with genomes > 200 kb than the "viral fraction." The longest complete genomes of jumbo phage (~ 252 kb) and giant virus (~ 716 kb) were both detected only in the "cellular fraction." Moreover, a relatively higher proportion of proviruses were predicted within the "cellular fraction" than "viral fraction." Besides the substantial divergence in viral community structure, the different fractions also contained their unique viral auxiliary metabolic genes; e.g., those potentially participating in inorganic carbon fixation in deep sea were detected only in the "cellular-fraction" viromes. In addition, there was a considerable divergence in the community structure of both "cellular fraction" and "viral fraction" viromes between the surface and deep-sea habitats, suggesting that they might have similar environmental adaptation properties. The findings deepen our understanding of the complexity of viral community structure and function in the ocean.

Genomic Analysis Unveils the Pervasiveness and Diversity of Prophages Infecting Erwinia Species

Prophages are abundant elements integrated into bacterial genomes and contribute to inter-strain genetic variability and, in some cases, modulate the environmental behavior of bacteria, such as pathogen virulence. Here, we described prophage occurrence and diversity in publicly available Erwinia genome assemblies, a genus containing plant pathogens. Prophage-like sequences were identified and taxonomically classified. Sequence diversity was analyzed through intergenomic similarities. Furthermore, we searched for anti-phage defense systems in Erwinia spp., such as DISARM, BREX, and CRISPR-Cas systems, and identified the putative targets of CRISPR spacers. We identified 939 prophage-like sequences in 221 Erwinia spp. genome assemblies. Only 243 prophage-like sequences were classified, all belonging to the Caudoviricetes class. The set of putative Erwinia prophages was mostly unique since only three sequences showed more than 70% intergenomic similarities to known Erwinia phages. Overall, the number and type of CRISPR-Cas systems were conserved within Erwinia species, with many spacers directed to the putative prophages identified. This study increased the knowledge of the diversity and distribution of Erwinia prophages, contributing to the characterization of genetic and ecological factors influencing Erwinia spp. environmental fitness.

Phage family classification under Caudoviricetes: A review of current tools using the latest ICTV classification framework

Bacteriophages, which are viruses infecting bacteria, are the most ubiquitous and diverse entities in the biosphere. There is accumulating evidence revealing their important roles in shaping the structure of various microbiomes. Thanks to (viral) metagenomic sequencing, a large number of new bacteriophages have been discovered. However, lacking a standard and automatic virus classification pipeline, the taxonomic characterization of new viruses seriously lag behind the sequencing efforts. In particular, according to the latest version of ICTV, several large phage families in the previous classification system are removed. Therefore, a comprehensive review and comparison of taxonomic classification tools under the new standard are needed to establish the state-of-the-art. In this work, we retrained and tested four recently published tools on newly labeled databases. We demonstrated their utilities and tested them on multiple datasets, including the RefSeq, short contigs, simulated metagenomic datasets, and low-similarity datasets. This study provides a comprehensive review of phage family classification in different scenarios and a practical guidance for choosing appropriate taxonomic classification pipelines. To our best knowledge, this is the first review conducted under the new ICTV classification framework. The results show that the new family classification framework overall leads to better conserved groups and thus makes family-level classification more feasible.

Climate-Endangered Arctic Epishelf Lake Harbors Viral Assemblages with Distinct Genetic Repertoires

Milne Fiord, located on the coastal margin of the Last Ice Area (LIA) in the High Arctic (82°N, Canada), harbors an epishelf lake, a rare type of ice-dependent ecosystem in which a layer of freshwater overlies marine water connected to the open ocean. This microbe-dominated ecosystem faces catastrophic change due to the deterioration of its ice environment related to warming temperatures. We produced the first assessment of viral abundance, diversity, and distribution in this vulnerable ecosystem and explored the niches available for viral taxa and the functional genes underlying their distribution. We found that the viral community in the freshwater layer was distinct from, and more diverse than, the community in the underlying seawater and contained a different set of putative auxiliary metabolic genes, including the sulfur starvation-linked gene tauD and the gene coding for patatin-like phospholipase. The halocline community resembled the freshwater more than the marine community, but harbored viral taxa unique to this layer. We observed distinct viral assemblages immediately below the halocline, at a depth that was associated with a peak of prasinophyte algae and the viral family Phycodnaviridae. We also assembled 15 complete circular genomes, including a putative Pelagibacter phage with a marine distribution. It appears that despite its isolated and precarious situation, the varied niches in this epishelf lake support a diverse viral community, highlighting the importance of characterizing underexplored microbiota in the Last Ice Area before these ecosystems undergo irreversible change.

IMPORTANCE Viruses are key to understanding polar aquatic ecosystems, which are dominated by microorganisms. However, studies of viral communities are challenging to interpret because the vast majority of viruses are known only from sequence fragments, and their taxonomy, hosts, and genetic repertoires are unknown. Our study establishes a basis for comparison that will advance understanding of viral ecology in diverse global environments, particularly in the High Arctic. Rising temperatures in this region mean that researchers have limited time remaining to understand the biodiversity and biogeochemical cycles of ice-dependent environments and the consequences of these rapid, irreversible changes. The case of the Milne Fiord epishelf lake has special urgency because of the rarity of this type of “floating lake” ecosystem and its location in the Last Ice Area, a region of thick sea ice with global importance for conservation efforts.

Genomes of six viruses that infect Asgard archaea from deep-sea sediments

Asgard archaea are globally distributed prokaryotic microorganisms related to eukaryotes; however, viruses that infect these organisms have not been described. Here, using metagenome sequences recovered from deep-sea hydrothermal sediments, we characterize six relatively large (up to 117 kb) double-stranded DNA (dsDNA) viral genomes that infected two Asgard archaeal phyla, Lokiarchaeota and Helarchaeota. These viruses encode Caudovirales-like structural proteins, as well as proteins distinct from those described in known archaeal viruses. Their genomes contain around 1-5% of genes associated with eukaryotic nucleocytoplasmic large DNA viruses (NCLDVs) and appear to be capable of semi-autonomous genome replication, repair, epigenetic modifications and transcriptional regulation. Moreover, Helarchaeota viruses may hijack host ubiquitin systems similar to eukaryotic viruses. Genomic analysis of these Asgard viruses reveals that they contain features of both prokaryotic and eukaryotic viruses, and provides insights into their potential infection and host interaction mechanisms.

Thousands of small, novel genes predicted in global phage genomes

Small genes (<150 nucleotides) have been systematically overlooked in phage genomes. We employ a large-scale comparative genomics approach to predict >40,000 small-gene families in ∼2.3 million phage genome contigs. We find that small genes in phage genomes are approximately 3-fold more prevalent than in host prokaryotic genomes. Our approach enriches for small genes that are translated in microbiomes, suggesting the small genes identified are coding. More than 9,000 families encode potentially secreted or transmembrane proteins, more than 5,000 families encode predicted anti-CRISPR proteins, and more than 500 families encode predicted antimicrobial proteins. By combining homology and genomic-neighborhood analyses, we reveal substantial novelty and diversity within phage biology, including small phage genes found in multiple host phyla, small genes encoding proteins that play essential roles in host infection, and small genes that share genomic neighborhoods and whose encoded proteins may share related functions.

Computational Tools for the Analysis of Uncultivated Phage Genomes

Over a century of bacteriophage research has uncovered a plethora of fundamental aspects of their biology, ecology, and evolution. Furthermore, the introduction of community-level studies through metagenomics has revealed unprecedented insights on the impact that phages have on a range of ecological and physiological processes. It was not until the introduction of viral metagenomics that we began to grasp the astonishing breadth of genetic diversity encompassed by phage genomes. Novel phage genomes have been reported from a diverse range of biomes at an increasing rate, which has prompted the development of computational tools that support the multilevel characterization of these novel phages based solely on their genome sequences. The impact of these technologies has been so large that, together with MAGs (Metagenomic Assembled Genomes), we now have UViGs (Uncultivated Viral Genomes), which are now officially recognized by the International Committee for the Taxonomy of Viruses (ICTV), and new taxonomic groups can now be created based exclusively on genomic sequence information. Even though the available tools have immensely contributed to our knowledge of phage diversity and ecology, the ongoing surge in software programs makes it challenging to keep up with them and the purpose each one is designed for. Therefore, in this review, we describe a comprehensive set of currently available computational tools designed for the characterization of phage genome sequences, focusing on five specific analyses: (i) assembly and identification of phage and prophage sequences, (ii) phage genome annotation, (iii) phage taxonomic classification, (iv) phage-host interaction analysis, and (v) phage microdiversity.

CHERRY: a Computational metHod for accuratE pRediction of virus-pRokarYotic interactions using a graph encoder-decoder model

Prokaryotic viruses, which infect bacteria and archaea, are key players in microbial communities. Predicting the hosts of prokaryotic viruses helps decipher the dynamic relationship between microbes. Experimental methods for host prediction cannot keep pace with the fast accumulation of sequenced phages. Thus, there is a need for computational host prediction. Despite some promising results, computational host prediction remains a challenge because of the limited known interactions and the sheer amount of sequenced phages by high-throughput sequencing technologies. The state-of-the-art methods can only achieve 43% accuracy at the species level. In this work, we formulate host prediction as link prediction in a knowledge graph that integrates multiple protein and DNA-based sequence features. Our implementation named CHERRY can be applied to predict hosts for newly discovered viruses and to identify viruses infecting targeted bacteria. We demonstrated the utility of CHERRY for both applications and compared its performance with 11 popular host prediction methods. To our best knowledge, CHERRY has the highest accuracy in identifying virus–prokaryote interactions. It outperforms all the existing methods at the species level with an accuracy increase of 37%. In addition, CHERRY’s performance on short contigs is more stable than other tools.

Novel Viral Communities Potentially Assisting in Carbon, Nitrogen, and Sulfur Metabolism in the Upper Slope Sediments of Mariana Trench

Viruses are ubiquitous in the oceans. Even in the deep sediments of the Mariana Trench, viruses have high productivity. However, little is known about their species composition and survival strategies in that environment. Here, we uncovered novel viral communities (3,206 viral scaffolds) in the upper slope sediments of the Mariana Trench via metagenomic analysis of 15 sediment samples. Most (99%) of the viral scaffolds lack known viral homologs, and ca. 59% of the high-quality viral genomes (total of 111 with completeness of >90%) represent novel genera, including some Phycodnaviridae and jumbo phages. These viruses contain various auxiliary metabolic genes (AMGs) potentially involved in organic carbon degradation, inorganic carbon fixation, denitrification, and assimilatory sulfate reduction, etc. This study provides novel insight into the almost unknown benthic viral communities in the Mariana Trench. IMPORTANCE The Mariana Trench harbors a substantial number of infective viral particles. However, very little is known about the identity, survival strategy, and potential functions of viruses in the trench sediments. Here, through metagenomic analysis, unusual benthic viral communities with high diversity and novelty were discovered. Among them, 59% of the viruses with a genome completeness of >90% represent novel genera. Various auxiliary metabolic genes carried by these viruses reflect the potential adaptive characteristics of viruses in this extreme environment and the biogeochemical cycles that they may participate in. This study gives us a deeper understanding of the peculiarities of viral communities in deep-sea/hadal sediments.

OUP accepted manuscript

Motivation

Phage–host associations play important roles in microbial communities. But in natural communities, as opposed to culture-based lab studies where phages are discovered and characterized metagenomically, their hosts are generally not known. Several programs have been developed for predicting which phage infects which host based on various sequence similarity measures or machine learning approaches. These are often based on whole viral and host genomes, but in metagenomics-based studies, we rarely have whole genomes but rather must rely on contigs that are sometimes as short as hundreds of bp long. Therefore, we need programs that predict hosts of phage contigs on the basis of these short contigs. Although most existing programs can be applied to metagenomic datasets for these predictions, their accuracies are generally low. Here, we develop ContigNet, a convolutional neural network-based model capable of predicting phage–host matches based on relatively short contigs, and compare it to previously published VirHostMatcher (VHM) and WIsH.

Results

On the validation set, ContigNet achieves 72–85% area under the receiver operating characteristic curve (AUROC) scores, compared to the maximum of 68% by VHM or WIsH for contigs of lengths between 200 bps to 50 kbps. We also apply the model to the Metagenomic Gut Virus (MGV) catalogue, a dataset containing a wide range of draft genomes from metagenomic samples and achieve 60–70% AUROC scores compared to that of VHM and WIsH of 52%. Surprisingly, ContigNet can also be used to predict plasmid-host contig associations with high accuracy, indicating a similar genetic exchange between mobile genetic elements and their hosts.

Availability and implementation

The source code of ContigNet and related datasets can be downloaded from https://github.com/tianqitang1/ContigNet.

iVirus 2.0: Cyberinfrastructure-supported tools and data to power DNA virus ecology

Microbes drive myriad ecosystem processes, but under strong influence from viruses. Because studying viruses in complex systems requires different tools than those for microbes, they remain underexplored. To combat this, we previously aggregated double-stranded DNA (dsDNA) virus analysis capabilities and resources into 'iVirus' on the CyVerse collaborative cyberinfrastructure. Here we substantially expand iVirus's functionality and accessibility, to iVirus 2.0, as follows. First, core iVirus apps were integrated into the Department of Energy's Systems Biology KnowledgeBase (KBase) to provide an additional analytical platform. Second, at CyVerse, 20 software tools (apps) were upgraded or added as new tools and capabilities. Third, nearly 20-fold more sequence reads were aggregated to capture new data and environments. Finally, documentation, as "live" protocols, was updated to maximize user interaction with and contribution to infrastructure development. Together, iVirus 2.0 serves as a uniquely central and accessible analytical platform for studying how viruses, particularly dsDNA viruses, impact diverse microbial ecosystems.

Predicting the hosts of prokaryotic viruses using GCN-based semi-supervised learning

Background

Prokaryotic viruses, which infect bacteria and archaea, are the most abundant and diverse biological entities in the biosphere. To understand their regulatory roles in various ecosystems and to harness the potential of bacteriophages for use in therapy, more knowledge of viral-host relationships is required. High-throughput sequencing and its application to the microbiome have offered new opportunities for computational approaches for predicting which hosts particular viruses can infect. However, there are two main challenges for computational host prediction. First, the empirically known virus-host relationships are very limited. Second, although sequence similarity between viruses and their prokaryote hosts have been used as a major feature for host prediction, the alignment is either missing or ambiguous in many cases. Thus, there is still a need to improve the accuracy of host prediction.

Results

In this work, we present a semi-supervised learning model, named HostG, to conduct host prediction for novel viruses. We construct a knowledge graph by utilizing both virus-virus protein similarity and virus-host DNA sequence similarity. Then graph convolutional network (GCN) is adopted to exploit viruses with or without known hosts in training to enhance the learning ability. During the GCN training, we minimize the expected calibrated error (ECE) to ensure the confidence of the predictions. We tested HostG on both simulated and real sequencing data and compared its performance with other state-of-the-art methods specifically designed for virus host classification (VHM-net, WIsH, PHP, HoPhage, RaFAH, vHULK, and VPF-Class).

Conclusion

HostG outperforms other popular methods, demonstrating the efficacy of using a GCN-based semi-supervised learning approach. A particular advantage of HostG is its ability to predict hosts from new taxa.

Supplementary Information

The online version contains supplementary material available at (10.1186/s12915-021-01180-4).