Metagenomic Analysis of the Diversity of DNA Viruses in the Surface and Deep Sea of the South China Sea

Metagenome sequence data mining for viral interaction studies: Review on progress and prospects

Metagenomics has been greatly accelerated by the development of next-generation sequencing (NGS) technologies, which allow scientists to discover and describe novel microorganisms without the need for conventional culture techniques. Examining integrative bioinformatics methods used in viral interaction research, this study highlights metagenomic data from various contexts. Accurate viral identification depends on high-purity genetic material extraction, appropriate NGS platform selection, and sophisticated bioinformatics tools like VirPipe and VirFinder. The efficiency and precision of metagenomic analysis are further improved with the advent of AI-based techniques. The diversity and dynamics of viral communities are demonstrated by case studies from a variety of environments, emphasizing the seasonal and geographical variations that influence viral populations. In addition to speeding up the discovery of new viruses, metagenomics offers thorough understanding of virus-host interactions and their ecological effects. This review provides a promising framework for comprehending the complexity of viral communities and their interactions with hosts, highlighting the transformational potential of metagenomics and bioinformatics in viral research.

Novel phage infecting the Roseobacter CHUG lineage reveals a diverse and globally distributed phage family

Bacteriophages play an essential role in shaping the diversity and metabolism of bacterial communities. Marine Roseobacter group is an abundant heterotrophic bacterial group that is involved in many major element cycles, especially carbon and sulfur. Members of the Roseobacter CHUG (Clade Hidden and Underappreciated Globally) lineage are globally distributed and are activated in pelagic marine environments. In this study, we isolated and characterized a phage, CRP-810, that infects the CHUG strain FZCC0198. The genome of CRP-810 was dissimilar to those of other known phages. Additionally, 251 uncultured viral genomes (UViGs) closely related to CRP-810 were obtained from the uncultivated marine viral contig databases. Comparative genomic and phylogenetic analyses revealed that CRP-810 and these related UViGs exhibited conserved genome synteny, representing a new phage family with at least eight subgroups. Most of the CRP-810-type phages contain an integrase gene, and CRP-810 can be integrated into the host genome. Further analysis revealed that three CRP-810-type members were prophages found in the genomes of marine SAR11, Poseidonocella, and Sphingomonadaceae. Finally, viromic read-mapping analysis showed that CRP-810-type phages were globally distributed and displayed distinct biogeographic patterns related to temperature and latitude. Many members with a lower G + C content were mainly distributed in the trade station, whereas members with a higher G + C content were mainly distributed in polar and westerlies station, indicating that the niche differentiation of phages was subject to host adaptation. Collectively, these findings identify a novel phage family and expand our understanding of phylogenetic diversity, evolution, and biogeography of marine phages.

IMPORTANCE

The Roseobacter CHUG lineage, affiliated with the Pelagic Roseobacter Cluster (PRC), is widely distributed in the global oceans and is active in oligotrophic seawater. However, knowledge of the bacteriophages that infect CHUG members is limited. In this study, a CHUG phage, CRP-810, that infects the CHUG strain FZCC0198, was isolated and shown to have a novel genomic architecture. In addition, 251 uncultured viral genomes closely related to CRP-810 were recovered and included in the analyses. Phylogenomic analyses revealed that the CRP-810-type phages represent a new phage family containing at least eight genus-level subgroups. Members of this family were predicted to infect various marine bacteria. We also demonstrated that the CRP-810-type phages are widely distributed in global oceans and display distinct biogeographic patterns related to latitude. Collectively, this study provides important insights into the genomic organization, diversity, and ecology of a novel phage family that infect ecologically important bacteria in the global ocean.

Genome sequences of the first Autographiviridae phages infecting marine Roseobacter

The ubiquitous and abundant marine phages play critical roles in shaping the composition and function of bacterial communities, impacting biogeochemical cycling in marine ecosystems. Autographiviridae is among the most abundant and ubiquitous phage families in the ocean. However, studies on the diversity and ecology of Autographiviridae phages in marine environments are restricted to isolates that infect SAR11 bacteria and cyanobacteria. In this study, ten new roseophages that infect marine Roseobacter strains were isolated from coastal waters. These new roseophages have a genome size ranging from 38 917 to 42 634 bp and G+C content of 44.6-50 %. Comparative genomics showed that they are similar to known Autographiviridae phages regarding gene content and architecture, thus representing the first Autographiviridae roseophages. Phylogenomic analysis based on concatenated conserved genes showed that the ten roseophages form three distinct subgroups within the Autographiviridae, and sequence analysis revealed that they belong to eight new genera. Finally, viromic read-mapping showed that these new Autographiviridae phages are widely distributed in global oceans, mostly inhabiting polar and estuarine locations. This study has expanded the current understanding of the genomic diversity, evolution and ecology of Autographiviridae phages and roseophages. We suggest that Autographiviridae phages play important roles in the mortality and community structure of roseobacters, and have broad ecological applications.

Metagenome of Gut Microbiota Provides a Novel Insight into the Pathogenicity of Balantioides coli in Weaned Piglets

Balantioides coli plays an important role in the diarrhea of weaned piglets, but its pathogenic potential and interaction with gut microbes remain unclear. To investigate the impact of B. coli colonization on the gut bacterial structure and function of weaned piglets, a metagenomic analysis based on shotgun sequencing was performed on fresh fecal samples collected from ten B. coli-colonized piglets and eight B. coli-free ones in this study. The results showed that decreasing diversity and shifted composition and function of the bacterial community were detected in the weaned piglets infected by B. coli. In contrast to the B. coli-negative group, the relative abundances of some members of the Firmicutes phylum including Clostridium, Ruminococcus species, and Intestinimonas butyriciproducens, which produce short-chain fatty acids, were significantly reduced in the B. coli-positive group. Notably, some species of the Prevotella genus (such as Prevotella sp. CAG:604 and Prevotella stercorea) were significantly increased in abundance in the B. coli-positive piglets. A functional analysis of the gut microbiota demonstrated that the differential gene sets for the metabolism of carbohydrates and amino acids were abundant in both groups, and the more enriched pathways in B. coli-infected piglets were associated with the sugar-specific phosphotransferase system (PTS) and the two-component regulatory system, as well as lipopolysaccharide (LPS) biosynthesis. Furthermore, several species of Prevotella were significantly positively correlated to the synthesis of lipid A, leading to the exporting of endotoxins and, thereby, inducing inflammation in the intestines of weaned piglets. Taken together, these findings revealed that colonization by B. coli was distinctly associated with the dysbiosis of gut bacterial structure and function in weaned piglets. Lower relative abundances of Clostridiaceae and Ruminococcaceae and higher abundances of Prevotella species were biomarkers of B. coli infection in weaned piglets.

Metagenomic Analyses Reveal the Influence of Depth Layers on Marine Biodiversity on Tropical and Subtropical Regions

The emergence of open ocean global-scale studies provided important information about the genomics of oceanic microbial communities. Metagenomic analyses shed light on the structure of marine habitats, unraveling the biodiversity of different water masses. Many biological and environmental factors can contribute to marine organism composition, such as depth. However, much remains unknown about microbial communities' taxonomic and functional features in different water layer depths. Here, we performed a metagenomic analysis of 76 publicly available samples from the Tara Ocean Project, distributed in 8 collection stations located in tropical or subtropical regions, and sampled from three layers of depth (surface water layer-SRF, deep chlorophyll maximum layer-DCM, and mesopelagic zone-MES). The SRF and DCM depth layers are similar in abundance and diversity, while the MES layer presents greater diversity than the other layers. Diversity clustering analysis shows differences regarding the taxonomic content of samples. At the domain level, bacteria prevail in most samples, and the MES layer presents the highest proportion of archaea among all samples. Taken together, our results indicate that the depth layer influences microbial sample composition and diversity.

Diversity and potential function of pig gut DNA viruses

Viruses are ubiquitous in the gut of animals and play an important role in the ecology of the gut microbiome. The potential effects of these substances on the growth and development of the body are not fully known. Little is known about the effects of breeding environment on pig gut virome. Here, there are 3584 viral operational taxonomic units (vOTUs) longer than 5 kb identified by virus-enriched metagenome sequencing from 25 pig fecal samples. Only a small minority of vOTUs (11.16%) can be classified at the family level, and ∼50% of the genes could be annotated, supporting the concept of pig gut as reservoirs of substantial undescribed viral genetic diversity. The composition of pig gut virome in the six regions may be related to geography. There are only 20 viral clusters (VCs) shared among pig gut virome in six regions of Shanxi Province. These viruses rarely carry antibiotic resistance genes (ARGs). At the same time, they possess abundant auxiliary metabolic genes (AMGs) potentially involved in carbon, sulfur metabolism and cofactor biosynthesis, etc. This study has revealed the unique characteristics and potential function of pig gut DNA virome and established a foundation for the recognition of the viral roles in gut environment.

Spatiotemporal Dynamics of Coastal Viral Community Structure and Potential Biogeochemical Roles Affected by an Ulva prolifera Green Tide

The world's largest macroalgal green tide, caused by Ulva prolifera, has resulted in serious consequences for coastal waters of the Yellow Sea, China. Although viruses are considered to be one of the key factors in controlling microalgal bloom demise, understanding of the relationship between viral communities and the macroalgal green tide is still poor. Here, a Qingdao coastal virome (QDCV) time-series data set was constructed based on the metagenomic analysis of 17 DNA viromes along three coastal stations of the Yellow Sea, covering different stages of the green tide from Julian days 165 to 271. A total of 40,076 viral contigs were detected and clustered into 28,058 viral operational taxonomic units (vOTUs). About 84% of the vOTUs could not be classified, and 62% separated from vOTUs in other ecosystems. Green tides significantly influenced the spatiotemporal dynamics of the viral community structure, diversity, and potential functions. For the classified vOTUs, the relative abundance of Pelagibacter phages declined with the arrival of the bloom and rebounded after the bloom, while Synechococcus and Roseobacter phages increased, although with a time lag from the peak of their hosts. More than 80% of the vOTUs reached peaks in abundance at different specific stages, and the viral peaks were correlated with specific hosts at different stages of the green tide. Most of the viral auxiliary metabolic genes (AMGs) were associated with carbon and sulfur metabolism and showed spatiotemporal dynamics relating to the degradation of the large amount of organic matter released by the green tide. IMPORTANCE To the best of our knowledge, this study is the first to investigate the responses of viruses to the world's largest macroalgal green tide. It revealed the spatiotemporal dynamics of the unique viral assemblages and auxiliary metabolic genes (AMGs) following the variation and degradation of Ulva prolifera. These findings demonstrate a tight coupling between viral assemblages, and prokaryotic and eukaryotic abundances were influenced by the green tide.

Abundant and cosmopolitan lineage of cyanopodoviruses lacking a DNA polymerase gene

Cyanopodoviruses affect the mortality and population dynamics of the unicellular picocyanobacteria Prochlorococcus and Synechococcus, the dominant primary producers in the oceans. Known cyanopodoviruses all contain the DNA polymerase gene (DNA pol) that is important for phage DNA replication and widely used in field quantification and diversity studies. However, we isolated 18 cyanopodoviruses without identifiable DNA pol. They form a new MPP-C clade that was separated from the existing MPP-A, MPP-B, and P-RSP2 clades. The MPP-C phages have the smallest genomes (37.3-37.9 kb) among sequenced cyanophages, and show longer latent periods than the MPP-B phages. Metagenomic reads of both clades are highly abundant in surface waters, but the MPP-C phages show higher relative abundance in surface waters than in deeper waters, while MPP-B phages have higher relative abundance in deeper waters. Our study reveals that cyanophages with distinct genomic contents and infection kinetics can exhibit different depth profiles in the oceans.

Genomic analysis and characterization of phages infecting the marine Roseobacter CHAB-I-5 lineage reveal a globally distributed and abundant phage genus

Marine phages play an important role in marine biogeochemical cycles by regulating the death, physiological metabolism, and evolutionary trajectory of bacteria. The Roseobacter group is an abundant and important heterotrophic bacterial group in the ocean, and plays an important role in carbon, nitrogen, sulfur and phosphorus cycling. The CHAB-I-5 lineage is one of the most dominant Roseobacter lineages, but remains largely uncultured. Phages infecting CHAB-I-5 bacteria have not yet been investigated due to the lack of culturable CHAB-I-5 strains. In this study, we isolated and sequenced two new phages (CRP-901 and CRP-902) infecting the CHAB-I-5 strain FZCC0083. We applied metagenomic data mining, comparative genomics, phylogenetic analysis, and metagenomic read-mapping to investigate the diversity, evolution, taxonomy, and biogeography of the phage group represented by the two phages. The two phages are highly similar, with an average nucleotide identity of 89.17%, and sharing 77% of their open reading frames. We identified several genes involved in DNA replication and metabolism, virion structure, DNA packing, and host lysis from their genomes. Metagenomic mining identified 24 metagenomic viral genomes closely related to CRP-901 and CRP-902. Genomic comparison and phylogenetic analysis demonstrated that these phages are distinct from other known viruses, representing a novel genus-level phage group (CRP-901-type). The CRP-901-type phages do not contain DNA primase and DNA polymerase genes, but possess a novel bifunctional DNA primase-polymerase gene with both primase and polymerase activities. Read-mapping analysis showed that the CRP-901-type phages are widespread across the world's oceans and are most abundant in estuarine and polar waters. Their abundance is generally higher than other known roseophages and even higher than most pelagiphages in the polar region. In summary, this study has greatly expanded our understanding of the genetic diversity, evolution, and distribution of roseophages. Our analysis suggests that the CRP-901-type phage is an important and novel marine phage group that plays important roles in the physiology and ecology of roseobacters.

Viruses in Subsurface Environments

Over the past 20 years, our knowledge of virus diversity and abundance in subsurface environments has expanded dramatically through application of quantitative metagenomic approaches. In most subsurface environments, viral diversity and abundance rival viral diversity and abundance observed in surface environments. Most of these viruses are uncharacterized in terms of their hosts and replication cycles. Analysis of accessory metabolic genes encoded by subsurface viruses indicates that they evolved to replicate within the unique features of their environments. The key question remains: What role do these viruses play in the ecology and evolution of the environments in which they replicate? Undoubtedly, as more virologists examine the role of viruses in subsurface environments, new insights will emerge.

Phage-prokaryote coexistence strategy mediates microbial community diversity in the intestine and sediment microhabitats of shrimp culture pond ecosystem

Emerging evidence supports that the phage-prokaryote interaction drives ecological processes in various environments with different phage life strategies. However, the knowledge of phage-prokaryote interaction in the shrimp culture pond ecosystem (SCPE) is still limited. Here, the viral and prokaryotic community profiles at four culture stages in the intestine of Litopenaeus vannamei and cultural sediment microhabitats of SCPE were explored to elucidate the contribution of phage-prokaryote interaction in modulating microbial communities. The results demonstrated that the most abundant viral families in the shrimp intestine and sediment were Microviridae, Circoviridae, Inoviridae, Siphoviridae, Podoviridae, Myoviridae, Parvoviridae, Herelleviridae, Mimiviridae, and Genomoviridae, while phages dominated the viral community. The dominant prokaryotic genera were Vibrio, Formosa, Aurantisolimonas, and Shewanella in the shrimp intestine, and Formosa, Aurantisolimonas, Algoriphagus, and Flavobacterium in the sediment. The viral and prokaryotic composition of the shrimp intestine and sediment were significantly different at four culture stages, and the phage communities were closely related to the prokaryotic communities. Moreover, the phage-prokaryote interactions can directly or indirectly modulate the microbial community composition and function, including auxiliary metabolic genes and closed toxin genes. The interactional analysis revealed that phages and prokaryotes had diverse coexistence strategies in the shrimp intestine and sediment microhabitats of SCPE. Collectively, our findings characterized the composition of viral communities in the shrimp intestine and cultural sediment and revealed the distinct pattern of phage-prokaryote interaction in modulating microbial community diversity, which expanded our cognization of the phage-prokaryote coexistence strategy in aquatic ecosystems from the microecological perspective and provided theoretical support for microecological prevention and control of shrimp culture health management.

Virioplankton assemblages from challenger deep, the deepest place in the oceans

Hadal ocean biosphere, that is, the deepest part of the world’s oceans, harbors a unique microbial community, suggesting a potential uncovered co-occurring virioplankton assemblage. Herein, we reveal the unique virioplankton assemblages of the Challenger Deep, comprising 95,813 non-redundant viral contigs from the surface to the hadal zone. Almost all of the dominant viral contigs in the hadal zone were unclassified, potentially related to Alteromonadales and Oceanospirillales. 2,586 viral auxiliary metabolic genes from 132 different KEGG orthologous groups were mainly related to the carbon, nitrogen, sulfur, and arsenic metabolism. Lysogenic viral production and integrase genes were augmented in the hadal zone, suggesting the prevalence of viral lysogenic life strategy. Abundant rve genes in the hadal zone, which function as transposase in the caudoviruses, further suggest the prevalence of viral-mediated horizontal gene transfer. This study provides fundamental insights into the virioplankton assemblages of the hadal zone, reinforcing the necessity of incorporating virioplankton into the hadal biogeochemical cycles.

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The unique virioplankton assemblages of the Challenger Deep were revealed

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Virus encoded auxiliary metabolic genes relating to the biogeochemical cycling

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Viruses in deep and hadal zone tend to be lysogenic, and potentially mediate the horizontal gene transfer

ViBE: a hierarchical BERT model to identify eukaryotic viruses using metagenome sequencing data

Viruses are ubiquitous in humans and various environments and continually mutate themselves. Identifying viruses in an environment without cultivation is challenging; however, promoting the screening of novel viruses and expanding the knowledge of viral space is essential. Homology-based methods that identify viruses using known viral genomes rely on sequence alignments, making it difficult to capture remote homologs of the known viruses. To accurately capture viral signals from metagenomic samples, models are needed to understand the patterns encoded in the viral genomes. In this study, we developed a hierarchical BERT model named ViBE to detect eukaryotic viruses from metagenome sequencing data and classify them at the order level. We pre-trained ViBE using read-like sequences generated from the virus reference genomes and derived three fine-tuned models that classify paired-end reads to orders for eukaryotic deoxyribonucleic acid viruses and eukaryotic ribonucleic acid viruses. ViBE achieved higher recall than state-of-the-art alignment-based methods while maintaining comparable precision. ViBE outperformed state-of-the-art alignment-free methods for all test cases. The performance of ViBE was also verified using real sequencing datasets, including the vaginal virome.

Picorna-Like Viruses of the Havel River, Germany

To improve the understanding of the virome diversity of riverine ecosystems in metropolitan areas, a metagenome analysis was performed with water collected in June 2018 from the river Havel in Berlin, Germany. After enrichment of virus particles and RNA extraction, paired-end Illumina sequencing was conducted and assignment to virus groups and families was performed. This paper focuses on picorna-like viruses, the most diverse and abundant group of viruses with impact on human, animal, and environmental health. Here, we describe altogether 166 viral sequences ranging in size from 1 to 11.5 kb. The 71 almost complete genomes are comprised of one candidate iflavirus, one picornavirus, two polycipiviruses, 27 marnaviruses, 27 dicistro-like viruses, and 13 untypeable viruses. Many partial picorna-like virus sequences up to 10.2 kb were also investigated. The sequences of the Havel picorna-like viruses represent genomes of seven of eight so far known Picornavirales families. Detection of numerous distantly related dicistroviruses suggests the existence of additional, yet unexplored virus groups with dicistronic genomes, including few viruses with unusual genome layout. Of special interest is a clade of dicistronic viruses with capsid protein-encoding sequences at the 5′-end of the genome. Also, monocistronic viruses with similarity of their polymerase and capsid proteins to those of dicistroviruses are interesting. A second protein with NTP-binding site present in the polyprotein of solinviviruses and related viruses needs further attention. The results underline the importance to study the viromes of fluvial ecosystems. So far acknowledged marnaviruses have been isolated from marine organisms. However, the present study and available sequence data suggest that rivers and limnic habitats are relevant ecosystems with circulation of marnaviruses as well as a plethora of unknown picorna-like viruses.

Viral diversity and potential environmental risk in microplastic at watershed scale: Evidence from metagenomic analysis of plastisphere

Microplastics (MPs) have been considered as a new vector for the long-distance transport of pathogens in aquatic ecosystems. However, the composition of viral communities attached on MPs and their environmental risk are largely unknown. Here, we profiled the viral diversity and potential risk in five different MPs collected from the Beilun River based on metagenomic analysis. Nearly 2863 million raw reads were produced and assembled, and annotation resulted in the identification of 1719 different species of viruses in MPs. Viruses in polypropylene (PP) displayed the highest diversity, with about 250 specific viruses detected. Source tracking of viruses in MPs by the fast expectation-maximization microbial source tracking method (FEAST) demonstrated that viruses in upstream and downstream MPs are two major sources of viruses in estuary. Furthermore, the MP-type-dependent potential environmental risk of viruses was significant based on both antibiotic resistance genes (ARGs) and virulence factors (VFs) detected in viral metagenomes, and PP was confirmed with the highest potential environmental risk. This study reveals the high diversity and potential environmental risk of viruses in different MPs, and provides an important guidance for future environmental monitoring and understanding the potential risks associated with both viral transmission and MPs pollution.

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.

Food waste composting based on patented compost bins: Carbon dioxide and nitrous oxide emissions and the denitrifying community analysis

Mature compost and rice bran were used as bulking agents to perform Food Waste Rapid Composting (FWRC) in a patented composting bin. The characteristics of CO₂ and N₂O emission and the denitrifying community were investigated. The release of CO₂ and N₂O concentrated in the early composting stage and reduced greatly after 28 h, and the N₂O emission peak of the treatment with mature compost was 8.5 times higher than that of rice bran. The high N₂O generation resulted from massive denitrifying bacteria and NO_x^--N in the composting material. The relative abundances of denitrifiers, correspondingly genes of narG and nirK were much higher in the treatment with mature compost, which contributed to the N₂O emission. Moreover, the correlation matrices revealed that N₂O fluxes correlated well with moisture, pH, temperature, and the abundances of nirK and nosZ genes during FWRC.

Saline lakes on the Qinghai-Tibet Plateau harbor unique viral assemblages mediating microbial environmental adaption

The highest plateau on Earth, Qinghai-Tibet Plateau, contains thousands of lakes with broad salinity and diverse and unique microbial communities. However, little is known about their co-occurring viruses. Herein, we identify 4,560 viral Operational Taxonomic Units (vOTUs) from six viromes of three saline lakes on Qinghai-Tibet Plateau, with less than 1% that could be classified. Most of the predicted vOTUs were associated with the dominant bacterial and archaeal phyla. Virus-encoded auxiliary metabolic genes suggest that viruses influence microbial metabolisms of carbon, nitrogen, sulfur, and lipid; the antibiotic resistance mediation; and their salinity adaption. The six viromes clustered together with the ice core viromes and bathypelagic ocean viromes and might represent a new viral habitat. This study has revealed the unique characteristics and potential ecological roles of DNA viromes in the lakes of the highest plateau and established a foundation for the recognition of the viral roles in plateau lake ecosystems.

Viral Characteristics of the Warm Atlantic and Cold Arctic Water Masses in the Nordic Seas

Nordic Seas are the subarctic seas connecting the Arctic Ocean and North Atlantic Ocean with complex water masses, experiencing an abrupt climate change. Though knowledge of the marine virosphere has expanded rapidly, the diversity of viruses and their relationships with host cells and water masses in the Nordic Seas remain to be fully revealed. Here, we establish the Nordic Sea DNA virome (NSV) data set of 55,315 viral contigs including 1,478 unique viral populations from seven stations influenced by both the warm Atlantic and cold Arctic water masses. Caudovirales dominated in the seven NSVs, especially in the warm Atlantic waters. The major giant nucleocytoplasmic large DNA viruses (NCLDVs) contributed a significant proportion of the classified viral contigs in the NSVs (32.2%), especially in the cold Arctic waters (44.9%). The distribution patterns of Caudovirales and NCLDVs were a reflection of the community structure of their hosts in the corresponding water masses and currents. Latitude, pH, and flow speed were found to be key factors influencing the microbial communities and coinfluencing the variation of viral communities. Network analysis illustrated the tight coupling between the variation of viral communities and microbial communities in the Nordic Seas. This study suggests a probable linkage between viromes, host cells, and surface water masses from both the cool Arctic and warm Atlantic Oceans. IMPORTANCE This is a systematic study of Nordic Sea viromes using metagenomic analysis. The viral diversity, community structure, and their relationships with host cells and the complex water masses from both the cool Arctic and the warm Atlantic oceans were illustrated. The NCLDVs and Caudovirales are proposed as the viral characteristics of the cold Arctic and warm Atlantic waters, respectively. This study provides an important background for the viromes in the subarctic seas connecting the Arctic Ocean and North Atlantic Ocean and sheds light on their responses to abrupt climate change in the future.

A systematic review from basics to omics on bacteriophage applications in poultry production and processing

The growing human population is currently facing an unprecedented challenge on global food production and sustainability. Despite recognizing poultry as one of the most successful and rapidly growing food industries to address this challenge; poultry health and safety remain major issues that entail immediate attention. Bacterial diseases including colibacillosis, salmonellosis, and necrotic enteritis have become increasingly prevalent during poultry production. Likewise, outbreaks caused by consumption of undercooked poultry products contaminated with zoonotic bacterial pathogens such as Salmonella, Campylobacter and Listeria, are a serious public health concern. With antimicrobial resistance problem and restricted use of antibiotics in food producing animals, bacteriophages are increasingly recognized as an attractive natural antibacterial alternative. Bacteriophages have recently shown promising results to treat diseases in poultry, reduce contamination of carcasses, and enhance the safety of poultry products. Omics technologies have been successfully employed to accurately characterize bacteriophages and their genes/proteins important for interaction with bacterial hosts. In this review, the potential of using lytic bacteriophages to mitigate the risk of major poultry-associated bacterial pathogens are explored. This study also explores challenges associated with the adoption of this technology by industries. Furthermore, the impact of omics approaches on studying bacteriophages, their host interaction and applications is discussed.

Characterization and Genomic Analysis of Marinobacter Phage vB_MalS-PS3, Representing a New Lambda-Like Temperate Siphoviral Genus Infecting Algae-Associated Bacteria

Marinobacter is the abundant and important algal-associated and hydrocarbon biodegradation bacteria in the ocean. However, little knowledge about their phages has been reported. Here, a novel siphovirus, vB_MalS-PS3, infecting Marinobacter algicola DG893(T), was isolated from the surface waters of the western Pacific Ocean. Transmission electron microscopy (TEM) indicated that vB_MalS-PS3 has the morphology of siphoviruses. VB_MalS-PS3 was stable from −20 to 55°C, and with the latent and rise periods of about 80 and 10 min, respectively. The genome sequence of VB_MalS-PS3 contains a linear, double-strand 42,168-bp DNA molecule with a G + C content of 56.23% and 54 putative open reading frames (ORFs). Nineteen conserved domains were predicted by BLASTp in NCBI. We found that vB_MalS-PS3 represent an understudied viral group with only one known isolate. The phylogenetic tree based on the amino acid sequences of whole genomes revealed that vB_MalS-PS3 has a distant evolutionary relationship with other siphoviruses, and can be grouped into a novel viral genus cluster with six uncultured assembled viral genomes from metagenomics, named here as Marinovirus. This study of the Marinobacter phage vB_MalS-PS3 genome enriched the genetic database of marine bacteriophages, in addition, will provide useful information for further research on the interaction between Marinobacter phages and their hosts, and their relationship with algal blooms and hydrocarbon biodegradation in the ocean.

Viral footprints across Gulfs of Kathiawar Peninsula and Arabian Sea: Unraveled from pelagic sediment metagenomic data

Marine biosphere is one of the largest, diverse and dynamic system hosting numerous of microorganisms. Viruses being the most abundant under explored lifeforms in ocean, represent a reservoir of great genetic diversity. We report the metagenomic insights on the viral communities in the deep sediments of the two Gulfs of Gujarat i.e. Gulf of Khambhat and Gulf of Kutch, with one sample from Arabian Sea, treated as open sea control. The viral reads were filtered from the whole dataset, assembled and studied for viral diversity, which was visualized by Pavian. The sequences were checked for the viral abundance, diversity and functionality. The resulting viral taxonomic classification contained 6 orders, 8 families and 47 genera. The results revealed that the phages infecting Cyanobacterium, Bacillus and Vibrio dominated the sediments. Further, it was observed that majority of viral sequences belonged to double-stranded DNA phages. The present study attempts to provide a primary insight of the viral signals and potential genetic content in the Gulfs of Kathiawar.

Prophage Genomics and Ecology in the Family Rhodobacteraceae

Roseobacters are globally abundant bacteria with critical roles in carbon and sulfur biogeochemical cycling. Here, we identified 173 new putative prophages in 79 genomes of Rhodobacteraceae. These prophages represented 1.3 ± 0.15% of the bacterial genomes and had no to low homology with reference and metagenome-assembled viral genomes from aquatic and terrestrial ecosystems. Among the newly identified putative prophages, 35% encoded auxiliary metabolic genes (AMGs), mostly involved in secondary metabolism, amino acid metabolism, and cofactor and vitamin production. The analysis of integration sites and gene homology showed that 22 of the putative prophages were actually gene transfer agents (GTAs) similar to a GTA of Rhodobacter capsulatus. Twenty-three percent of the predicted prophages were observed in the TARA Oceans viromes generated from free viral particles, suggesting that they represent active prophages capable of induction. The distribution of these prophages was significantly associated with latitude and temperature. The prophages most abundant at high latitudes encoded acpP, an auxiliary metabolic gene involved in lipid synthesis and membrane fluidity at low temperatures. Our results show that prophages and gene transfer agents are significant sources of genomic diversity in roseobacter, with potential roles in the ecology of this globally distributed bacterial group.

A Novel Vibriophage vB_VcaS_HC Containing Lysogeny-Related Gene Has Strong Lytic Ability against Pathogenic Bacteria

To avoid the negative effects of antibiotics, using phage to prevent animal disease becomes a promising method in aquaculture. Here, a lytic phage provisionally named vB_VcaS_HC that can infect the pathogen (i.e., Vibrio campbellii 18) of prawn was isolated. The phage has an isometric head and a non-contractile tail. During phage infection, the induced host mortality in 5.5 h reached ca. 96%, with a latent period of 1.5 h and a burst size of 172 PFU/cell. It has an 81,566 bp circular dsDNA genome containing 121 open reading frames (ORFs), and ca. 71% of the ORFs are functionally unknown. Comparative genomic and phylogenetic analysis revealed that it is a novel phage belonging to Delepquintavirus, Siphoviridae, Caudovirales. In the phage genome, besides the ordinary genes related to structure assembly and DNA metabolism, there are 10 auxiliary metabolic genes. For the first time, the pyruvate phosphate dikinase (PPDK) gene was found in phages whose product is a key rate-limiting enzyme involving Embden-Meyerhof-Parnas (EMP) reaction. Interestingly, although the phage has a strong bactericidal activity and contains a potential lysogeny related gene, i.e., the recombinase (RecA) gene, we did not find the phage turned into a lysogenic state. Meanwhile, the phage genome does not contain any bacterial virulence gene or antimicrobial resistance gene. This study represents the first comprehensive characterization of a lytic V. campbellii phage and indicates that it is a promising candidate for the treatment of V. campbellii infections.

IMG/VR v3: an integrated ecological and evolutionary framework for interrogating genomes of uncultivated viruses

Viruses are integral components of all ecosystems and microbiomes on Earth. Through pervasive infections of their cellular hosts, viruses can reshape microbial community structure and drive global nutrient cycling. Over the past decade, viral sequences identified from genomes and metagenomes have provided an unprecedented view of viral genome diversity in nature. Since 2016, the IMG/VR database has provided access to the largest collection of viral sequences obtained from (meta)genomes. Here, we present the third version of IMG/VR, composed of 18 373 cultivated and 2 314 329 uncultivated viral genomes (UViGs), nearly tripling the total number of sequences compared to the previous version. These clustered into 935 362 viral Operational Taxonomic Units (vOTUs), including 188 930 with two or more members. UViGs in IMG/VR are now reported as single viral contigs, integrated proviruses or genome bins, and are annotated with a new standardized pipeline including genome quality estimation using CheckV, taxonomic classification reflecting the latest ICTV update, and expanded host taxonomy prediction. The new IMG/VR interface enables users to efficiently browse, search, and select UViGs based on genome features and/or sequence similarity. IMG/VR v3 is available at https://img.jgi.doe.gov/vr, and the underlying data are available to download at https://genome.jgi.doe.gov/portal/IMG_VR.

Yaravirus: A novel 80-nm virus infecting Acanthamoeba castellanii

Here we report the discovery of Yaravirus, a lineage of amoebal virus with a puzzling origin and evolution. Yaravirus presents 80-nm-sized particles and a 44,924-bp dsDNA genome encoding for 74 predicted proteins. Yaravirus genome annotation showed that none of its genes matched with sequences of known organisms at the nucleotide level; at the amino acid level, six predicted proteins had distant matches in the nr database. Complimentary prediction of three-dimensional structures indicated possible function of 17 proteins in total. Furthermore, we were not able to retrieve viral genomes closely related to Yaravirus in 8,535 publicly available metagenomes spanning diverse habitats around the globe. The Yaravirus genome also contained six types of tRNAs that did not match commonly used codons. Proteomics revealed that Yaravirus particles contain 26 viral proteins, one of which potentially representing a divergent major capsid protein (MCP) with a predicted double jelly-roll domain. Structure-guided phylogeny of MCP suggests that Yaravirus groups together with the MCPs of Pleurochrysis endemic viruses. Yaravirus expands our knowledge of the diversity of DNA viruses. The phylogenetic distance between Yaravirus and all other viruses highlights our still preliminary assessment of the genomic diversity of eukaryotic viruses, reinforcing the need for the isolation of new viruses of protists.

Diverse and unique viruses discovered in the surface water of the East China Sea

Background

Viruses are the most abundant biological entities on earth and play import roles in marine biogeochemical cycles. Here, viral communities in the surface water of the East China Sea (ECS) were collected from three representative regions of Yangshan Harbor (YSH), Gouqi Island (GQI), and the Yangtze River Estuary (YRE) and explored primarily through epifluorescence microscopy (EM), transmission electron microscopy (TEM), and metagenomics analysis.

Results

The virus-like particles (VLPs) in the surface water of the ECS were measured to be 10⁶ to 10⁷ VLPs/ml. Most of the isolated viral particles possessed a head-and-tail structure, but VLPs with unique morphotypes that had never before been observed in the realm of viruses were also found. The sequences related to known viruses in GenBank accounted for 21.1–22.8% of the viromic datasets from YSH, GQI, and YRE. In total, 1029 viral species were identified in the surface waters of the ECS. Among them, tailed phages turn out to make up the majority of viral communities, however a small number of Phycodnaviridae or Mimiviridae related sequences were also detected. The diversity of viruses did not appear to be a big difference among these three aquatic environments but their relative abundance was geographically variable. For example, the Pelagibacter phage HTVC010P accounted for 50.4% of the identified viral species in GQI, but only 9.1% in YSH and 11.7% in YRE. Sequences, almost identical to those of uncultured marine thaumarchaeal dsDNA viruses and magroviruses that infect Marine Group II Euryarchaeota, were confidently detected in the ECS viromes. The predominant classes of virome ORFs with functional annotations that were found were those involved in viral biogenesis. Virus-host connections, inferred from CRISPR spacer-protospacer mapping, implied newly discovered infection relationships in response to arms race between them.

Conclusions

Together, both identified viruses and unknown viral assemblages observed in this study were indicative of the complex viral community composition found in the ECS. This finding fills a major gap in the dark world of oceanic viruses of China and additionally contributes to the better understanding of global marine viral diversity, composition, and distribution.

A Review on Viral Metagenomics in Extreme Environments

Viruses are the most abundant biological entities in the biosphere, and have the ability to infect Bacteria, Archaea, and Eukaryotes. The virome is estimated to be at least ten times more abundant than the microbiome with 107 viruses per milliliter and 109 viral particles per gram in marine waters and sediments or soils, respectively. Viruses represent a largely unexplored genetic diversity, having an important role in the genomic plasticity of their hosts. Moreover, they also play a significant role in the dynamics of microbial populations. In recent years, metagenomic approaches have gained increasing popularity in the study of environmental viromes, offering the possibility of extending our knowledge related to both virus diversity and their functional characterization. Extreme environments represent an interesting source of both microbiota and their virome due to their particular physicochemical conditions, such as very high or very low temperatures and >1 atm hydrostatic pressures, among others. Despite the fact that some progress has been made in our understanding of the ecology of the microbiota in these habitats, few metagenomic studies have described the viromes present in extreme ecosystems. Thus, limited advances have been made in our understanding of the virus community structure in extremophilic ecosystems, as well as in their biotechnological potential. In this review, we critically analyze recent progress in metagenomic based approaches to explore the viromes in extreme environments and we discuss the potential for new discoveries, as well as methodological challenges and perspectives.