Infection strategy and biogeography distinguish cosmopolitan groups of marine jumbo bacteriophages

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.

Macroalgal virosphere assists with host-microbiome equilibrium regulation and affects prokaryotes in surrounding marine environments

The microbiomes in macroalgal holobionts play vital roles in regulating macroalgal growth and ocean carbon cycling. However, the virospheres in macroalgal holobionts remain largely underexplored, representing a critical knowledge gap. Here we unveil that the holobiont of kelp (Saccharina japonica) harbors highly specific and unique epiphytic/endophytic viral species, with novelty (99.7% unknown) surpassing even extreme marine habitats (e.g. deep-sea and hadal zones), indicating that macroalgal virospheres, despite being closest to us, are among the least understood. These viruses potentially maintain microbiome equilibrium critical for kelp health via lytic-lysogenic infections and the expression of folate biosynthesis genes. In-situ kelp mesocosm cultivation and metagenomic mining revealed that kelp holobiont profoundly reshaped surrounding seawater and sediment virus-prokaryote pairings through changing surrounding environmental conditions and virus-host migrations. Some kelp epiphytic viruses could even infect sediment autochthonous bacteria after deposition. Moreover, the presence of ample viral auxiliary metabolic genes for kelp polysaccharide (e.g. laminarin) degradation underscores the underappreciated viral metabolic influence on macroalgal carbon cycling. This study provides key insights into understanding the previously overlooked ecological significance of viruses within macroalgal holobionts and the macroalgae-prokaryotes-virus tripartite relationship.

Structural and Genomic Diversity of Bacteriophages

Bacteriophage diversity is a relatively unknown frontier that is rapidly being explored, leading to a wealth of new information. New bacteriophages are being discovered at an astounding rate via both phage isolation studies and metagenomic analyses. In addition, a nucleotide sequence-based viral taxonomic system has been developed to better handle this wealth of new information. As a result of these developments, phage scientists are transitioning from knowing that there must be huge numbers of diverse kinds of phage particles in natural environments to identifying the actual abundance and phage diversity that is present in specific environments. This review documents the beginning of this transition, offering a glimpse into the magnitude of change unfolding in the field. It stands as a testament to the expanding frontiers of phage research, illuminating the remarkable progress made in unraveling the intricate world of bacteriophage diversity and advancing our understanding of these enigmatic viral entities.

Phylogenetic diversity and functional potential of large and cell-associated viruses in the Bay of Bengal

IMPORTANCE

The BoB, the world's largest bay, is of significant economic importance to surrounding countries, particularly Bangladesh, which heavily relies on its coastal resources. Concurrently, the BoB holds substantial ecological relevance due to the region's high vulnerability to climate change-induced impacts. Yet, our understanding of the BoB's microbiome in relation to marine food web and biogeochemical cycling remains limited. Particularly, there are little or no data on the viral diversity and host association in the BoB. We examined the viral community in two distinct BoB coastal regions to reveal a multitude of viral species interacting with a wide range of microbial hosts, some of which play key roles in coastal biogeochemical cycling or potential pathogens. Furthermore, we demonstrate that the BoB coast harbors a diverse community of large and giant viruses, underscoring the importance of investigating understudied environments to discover novel viral lineages with complex metabolic capacities.

Contrasting drivers of abundant phage and prokaryotic communities revealed in diverse coastal ecosystems

Phages (viruses of bacteria and archaea) are a ubiquitous top-down control on microbial communities by selectively infecting and killing cells. As obligate parasites, phages are inherently linked to processes that impact their hosts' distribution and physiology, but phages can also be impacted by external, environmental factors, such as UV radiation degrading their virions. To better understand these complex links of phages to their hosts and the environment, we leverage the unique ecological context of the Isthmus of Panama, which narrowly disconnects the productive Tropical Eastern Pacific (EP) and nutrient-poor Tropical Western Atlantic (WA) provinces. We could thus compare patterns of phage and prokaryotic communities at both global scales (between oceans) and local-scales (between habitats within an ocean). Although both phage and prokaryotic communities differed sharply between the oceans, phage community composition did not significantly differ between mangroves and reefs of the WA, while prokaryotic communities were distinct. These results suggest phages are more shaped by dispersal processes than local conditions regardless of spatial scale, while prokaryotes tend to be shaped by local conditions at smaller spatial scales. Collectively, we provide a framework for addressing the co-variability between phages and prokaryotes in marine systems and identifying factors that drive consistent versus disparate trends in community shifts, essential to informing models of biogeochemical cycles that include these interactions.

Genomic and proteomic characterization of vB_SauM-UFV_DC4, a novel Staphylococcus jumbo phage

Staphylococcus aureus is one of the most relevant mastitis pathogens in dairy cattle, and the acquisition of antimicrobial resistance genes presents a significant health issue in both veterinary and human fields. Among the different strategies to tackle S. aureus infection in livestock, bacteriophages have been thoroughly investigated in the last decades; however, few specimens of the so-called jumbo phages capable of infecting S. aureus have been described. Herein, we report the biological, genomic, and structural proteomic features of the jumbo phage vB_SauM-UFV_DC4 (DC4). DC4 exhibited a remarkable killing activity against S. aureus isolated from the veterinary environment and stability at alkaline conditions (pH 4 to 12). The complete genome of DC4 is 263,185 bp (GC content: 25%), encodes 263 predicted CDSs (80% without an assigned function), 1 tRNA (Phe-tRNA), multisubunit RNA polymerase, and an RNA-dependent DNA polymerase. Moreover, comparative analysis revealed that DC4 can be considered a new viral species belonging to a new genus DC4 and showed a similar set of lytic proteins and depolymerase activity with closely related jumbo phages. The characterization of a new S. aureus jumbo phage increases our understanding of the diversity of this group and provides insights into the biotechnological potential of these viruses. KEY POINTS: • vB_SauM-UFV_DC4 is a new viral species belonging to a new genus within the class Caudoviricetes. • vB_SauM-UFV_DC4 carries a set of RNA polymerase subunits and an RNA-directed DNA polymerase. • vB_SauM-UFV_DC4 and closely related jumbo phages showed a similar set of lytic proteins.

Viral metagenomics reveals diverse virus-host interactions throughout the soil depth profile

IMPORTANCE

Soil viruses can moderate the roles that their host microbes play in global carbon cycling. However, given that most studies investigate the surface layer (i.e., top 20 cm) of soil, the extent to which this occurs in subsurface soil (i.e., below 20 cm) is unknown. Here, we leveraged public sequencing data to investigate the interactions between viruses and their hosts at soil depth intervals, down to 115 cm. While most viruses were detected throughout the soil depth profile, their adaptation to host microbes varied. Nonetheless, we uncovered evidence for the potential of soil viruses to encourage their hosts to recycle plant-derived carbon in both surface and subsurface soils. This work reasons that our understanding of soil viral functions requires us to continue to dig deeper and compare viruses existing throughout soil ecosystems.

Automated classification of giant virus genomes using a random forest model built on trademark protein families

Viruses of the phylum Nucleocytoviricota , often referred to as "giant viruses," are prevalent in various environments around the globe and play significant roles in shaping eukaryotic diversity and activities in global ecosystems. Given the extensive phylogenetic diversity within this viral group and the highly complex composition of their genomes, taxonomic classification of giant viruses, particularly incomplete metagenome-assembled genomes (MAGs) can present a considerable challenge. Here we developed TIGTOG ( T axonomic Information of G iant viruses using T rademark O rthologous G roups), a machine learning-based approach to predict the taxonomic classification of novel giant virus MAGs based on profiles of protein family content. We applied a random forest algorithm to a training set of 1,531 quality-checked, phylogenetically diverse Nucleocytoviricota genomes using pre-selected sets of giant virus orthologous groups (GVOGs). The classification models were predictive of viral taxonomic assignments with a cross-validation accuracy of 99.6% to the order level and 97.3% to the family level. We found that no individual GVOGs or genome features significantly influenced the algorithm's performance or the models' predictions, indicating that classification predictions were based on a comprehensive genomic signature, which reduced the necessity of a fixed set of marker genes for taxonomic assigning purposes. Our classification models were validated with an independent test set of 823 giant virus genomes with varied genomic completeness and taxonomy and demonstrated an accuracy of 98.6% and 95.9% to the order and family level, respectively. Our results indicate that protein family profiles can be used to accurately classify large DNA viruses at different taxonomic levels and provide a fast and accurate method for the classification of giant viruses. This approach could easily be adapted to other viral groups.

Virologs, viral mimicry, and virocell metabolism: the expanding scale of cellular functions encoded in the complex genomes of giant viruses

The phylum Nucleocytoviricota includes the largest and most complex viruses known. These "giant viruses" have a long evolutionary history that dates back to the early diversification of eukaryotes, and over time they have evolved elaborate strategies for manipulating the physiology of their hosts during infection. One of the most captivating of these mechanisms involves the use of genes acquired from the host-referred to here as viral homologs or "virologs"-as a means of promoting viral propagation. The best-known examples of these are involved in mimicry, in which viral machinery "imitates" immunomodulatory elements in the vertebrate defense system. But recent findings have highlighted a vast and rapidly expanding array of other virologs that include many genes not typically found in viruses, such as those involved in translation, central carbon metabolism, cytoskeletal structure, nutrient transport, vesicular trafficking, and light harvesting. Unraveling the roles of virologs during infection as well as the evolutionary pathways through which complex functional repertoires are acquired by viruses are important frontiers at the forefront of giant virus research.

Characterization and genomic analysis of an oceanic cyanophage infecting marine Synechococcus reveal a novel genus

Cyanophages play a crucial role in the biogeochemical cycles of aquatic ecosystems by affecting the population dynamics and community structure of cyanobacteria. In this study, a novel cyanophage, Nanhaivirus ms29, that infects Synechococcus sp. MW02 was isolated from the ocean basin in the South China Sea. It was identified as a T4-like phage using transmission electron microscopy. Phylogenetic analysis demonstrated that this cyanophage is distinct from other known T4-like cyanophage, belonging to a novel genus named Nanhaivirus within the family Kyanoviridae, according to the most recent classification proposed by the International Committee on Taxonomy of Viruses (ICTV). The genome of this novel cyanophage is composed of 178,866 bp of double-stranded DNA with a G + C content of 42.5%. It contains 217 potential open reading frames (ORFs) and 6 tRNAs. As many as 30 auxiliary metabolic genes (AMGs) were identified in the genome, which related to photosynthesis, carbon metabolism, nutrient uptake and stress tolerance, possibly reflecting a genomic adaption to the oligotrophic environment. Read-mapping analysis showed that Nanhaivirus ms29 mainly distributed in temperate and tropical epipelagic waters. This study enriches of the virus gene database of cyanophages and provides valuable insights into the phylogeny of cyanophages and their interactions with their hosts.

Assessing the biogeography of marine giant viruses in four oceanic transects

Viruses of the phylum Nucleocytoviricota are ubiquitous in ocean waters and play important roles in shaping the dynamics of marine ecosystems. In this study, we leveraged the bioGEOTRACES metagenomic dataset collected across the Atlantic and Pacific Oceans to investigate the biogeography of these viruses in marine environments. We identified 330 viral genomes, including 212 in the order Imitervirales and 54 in the order Algavirales. We found that most viruses appeared to be prevalent in shallow waters (<150 m), and that viruses of the Mesomimiviridae (Imitervirales) and Prasinoviridae (Algavirales) are by far the most abundant and diverse groups in our survey. Five mesomimiviruses and one prasinovirus are particularly widespread in oligotrophic waters; annotation of these genomes revealed common stress response systems, photosynthesis-associated genes, and oxidative stress modulation genes that may be key to their broad distribution in the pelagic ocean. We identified a latitudinal pattern in viral diversity in one cruise that traversed the North and South Atlantic Ocean, with viral diversity peaking at high latitudes of the northern hemisphere. Community analyses revealed three distinct Nucleocytoviricota communities across latitudes, categorized by latitudinal distance towards the equator. Our results contribute to the understanding of the biogeography of these viruses in marine systems.

Mirusviruses link herpesviruses to giant viruses

DNA viruses have a major influence on the ecology and evolution of cellular organisms1-4, but their overall diversity and evolutionary trajectories remain elusive5. Here we carried out a phylogeny-guided genome-resolved metagenomic survey of the sunlit oceans and discovered plankton-infecting relatives of herpesviruses that form a putative new phylum dubbed Mirusviricota. The virion morphogenesis module of this large monophyletic clade is typical of viruses from the realm Duplodnaviria6, with multiple components strongly indicating a common ancestry with animal-infecting Herpesvirales. Yet, a substantial fraction of mirusvirus genes, including hallmark transcription machinery genes missing in herpesviruses, are closely related homologues of giant eukaryotic DNA viruses from another viral realm, Varidnaviria. These remarkable chimaeric attributes connecting Mirusviricota to herpesviruses and giant eukaryotic viruses are supported by more than 100 environmental mirusvirus genomes, including a near-complete contiguous genome of 432 kilobases. Moreover, mirusviruses are among the most abundant and active eukaryotic viruses characterized in the sunlit oceans, encoding a diverse array of functions used during the infection of microbial eukaryotes from pole to pole. The prevalence, functional activity, diversification and atypical chimaeric attributes of mirusviruses point to a lasting role of Mirusviricota in the ecology of marine ecosystems and in the evolution of eukaryotic DNA viruses.

Metagenomics reveals the increased antibiotics resistome through prokaryote rather than virome after overuse of rare earth element compounds

Rare earth elements (REE) are extensively exploited in the agricultural ecosystems due to their various beneficial roles on plant growth. However, the ecotoxicological effects and environmental risk of REE are poorly assessed. Here, we investigated the effects of lanthanum and cerium nitrate on soil prokaryote and viral metal resistance genes (MRGs) and antibiotics resistance genes (ARGs) using a metagenomic-based approach. We found that relative abundances of prokaryote phyla Bacteroidetes and Chloroflexi decreased with increasing of both REE compounds. In addition, low level REE nitrate (0.05 and 0.1 mmol kg^-1 soil) inhibited the viral family Phycodanaviridae, Rudiviridae, Schitoviridae, whereas high level (0.16 and 0.32 mmol kg^-1 soil) REE nitrate suppressed the viral family Herelleviridae, Iridoviridae, Podoviridae. ARGs were not significantly affected by low level of REE nitrate. However, high level of both REEs nitrate increased the abundances of dominant prokaryote genes resisting to most of the drug classes, such as aminoglycoside, elfamycin, fluoroquinolone, macrolide, rifamycin. Abundance of MRGs in prokaryote did not change consistently with REE nitrate compound type and input rate. MRGs were only partially detected in the virome in some of the treatments, while ARGs was not detected in virome. Together, we demonstrated that overuse of REE nitrate in agriculture would increase the risk of dissemination of ARGs through prokaryotes but not virus, although viral community was substantially shifted.

Assessing the biogeography of marine giant viruses in four oceanic transects

Viruses of the phylum Nucleocytoviricota are ubiquitous in ocean waters and play important roles in shaping the dynamics of marine ecosystems. In this study, we leveraged the bioGEOTRACES metagenomic dataset collected across the Atlantic and Pacific Oceans to investigate the biogeography of these viruses in marine environments. We identified 330 viral genomes, including 212 in the order Imitervirales and 54 in the order Algavirales . We found that most viruses appeared to be prevalent in shallow waters (<150 meters), and that viruses of the Mesomimiviridae ( Imitervirales ) and Prasinoviridae ( Algavirales ) are by far the most abundant and diverse groups in our survey. Five mesomimiviruses and one prasinovirus are particularly widespread in oligotrophic waters; annotation of these genomes revealed common stress response systems, photosynthesis-associated genes, and oxidative stress modulation that may be key to their broad distribution in the pelagic ocean. We identified a latitudinal pattern in viral diversity in one cruise that traversed the North and South Atlantic Ocean, with viral diversity peaking at high latitudes of the northern hemisphere. Community analyses revealed three distinct Nucleocytoviricota communities across latitudes, categorized by latitudinal distance towards the equator. Our results contribute to the understanding of the biogeography of these viruses in marine systems.

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.

Diversity and genomics of giant viruses in the North Pacific Subtropical Gyre

Large double-stranded DNA viruses of the phylum Nucleocytoviricota, often referred to as "giant viruses," are ubiquitous members of marine ecosystems that are important agents of mortality for eukaryotic plankton. Although giant viruses are known to be prevalent in marine systems, their activities in oligotrophic ocean waters remain unclear. Oligotrophic gyres constitute the majority of the ocean and assessing viral activities in these regions is therefore critical for understanding overall marine microbial processes. In this study, we generated 11 metagenome-assembled genomes (MAGs) of giant viruses from samples previously collected from Station ALOHA in the North Pacific Subtropical Gyre. Phylogenetic analyses revealed that they belong to the orders Imitervirales (n = 6), Algavirales (n = 4), and Pimascovirales (n = 1). Genome sizes ranged from ~119-574 kbp, and several of the genomes encoded predicted TCA cycle components, cytoskeletal proteins, collagen, rhodopsins, and proteins potentially involved in other cellular processes. Comparison with other marine metagenomes revealed that several have broad distribution across ocean basins and represent abundant viral constituents of pelagic surface waters. Our work sheds light on the diversity of giant viruses present in oligotrophic ocean waters across the globe.

Diversity and Ecology of Caudoviricetes Phages with Genome Terminal Repeats in Fecal Metagenomes from Four Dutch Cohorts

The human gut harbors numerous viruses infecting the human host, microbes, and other inhabitants of the gastrointestinal tract. Most of these viruses remain undiscovered, and their influence on human health is unknown. Here, we characterize viral genomes in gut metagenomic data from 1950 individuals from four population and patient cohorts. We focus on a subset of viruses that is highly abundant in the gut, remains largely uncharacterized, and allows confident complete genome identification—phages that belong to the class Caudoviricetes and possess genome terminal repeats. We detect 1899 species-level units belonging to this subset, 19% of which do not have complete representative genomes in major public gut virome databases. These units display diverse genomic features, are predicted to infect a wide range of microbial hosts, and on average account for <1% of metagenomic reads. Analysis of longitudinal data from 338 individuals shows that the composition of this fraction of the virome remained relatively stable over a period of 4 years. We also demonstrate that 54 species-level units are highly prevalent (detected in >5% of individuals in a cohort). Finally, we find 34 associations between highly prevalent phages and human phenotypes, 24 of which can be explained by the relative abundance of potential hosts.

Viral Complexity

Although traditionally viewed as streamlined and simple, discoveries over the last century have revealed that viruses can exhibit surprisingly complex physical structures, genomic organization, ecological interactions, and evolutionary histories. Viruses can have physical dimensions and genome lengths that exceed many cellular lineages, and their infection strategies can involve a remarkable level of physiological remodeling of their host cells. Virus–virus communication and widespread forms of hyperparasitism have been shown to be common in the virosphere, demonstrating that dynamic ecological interactions often shape their success. And the evolutionary histories of viruses are often fraught with complexities, with chimeric genomes including genes derived from numerous distinct sources or evolved de novo. Here we will discuss many aspects of this viral complexity, with particular emphasis on large DNA viruses, and provide an outlook for future research.