Our understanding of the diversity and abundance of circular replication associated protein (Rep) – encoding single stranded (CRESS) DNA viruses has increased considerably over the last few years due to a combination of modern sequencing technologies and new molecular tools. Studies have used these to identify and recover CRESS DNA viruses from a range of different marine organisms, including copepods, shrimp and molluscs. In our study we identify 79 novel CRESS DNA viruses from three mollusc species (Austrovenus stutchburyi, Paphies subtriangulata and Amphibola crenata) and benthic sediments from the Avon-Heathcote estuary in Christchurch, New Zealand. The genomes recovered have varying genome architectures, with all encoding at least two major ORFs that have either unidirectional or bidirectional organisation. Analysis of the Reps of the viral genomes showed they are all highly diverse, with only one Rep sequence sharing 65% amino acid identity with the Rep of gastropod-associated circular DNA virus (GaCSV). Our study adds significantly to the wealth of CRESS DNA viruses recovered from freshwater and marine environments and extends our knowledge of the distribution of these viruses.
Ed Rybicki's insight:
Geminivirologists: they get everywhere. Like ssDNA viruses B-)
Viruses are ubiquitous organisms, but their role in the ecosystem and their prevalence are still poorly understood. Mimiviruses are extremely complex and large DNA viruses. Although metagenomic studies have suggested that members of the family Mimiviridae are abundant in oceans, there is a lack of information about the association of mimiviruses with marine organisms. In this work, we demonstrate by molecular and virological methods that oysters are excellent sources for mimiviruses isolation. Our data not only provide new information about the biology of these viruses but also raise questions regarding the role of oyster consumption as a putative source of mimivirus infection in humans.
Mimivirus graphic courtesy of Russell Kightley Media
The family Marseilleviridae encompasses giant viruses that replicate in free-living Acanthamoebaamoebae. Since the discovery of the founding member Marseillevirus in 2007, 7 new marseilleviruses have been observed, including 3 from environmental freshwater, one from a dipteran, and two from symptom-free humans. Marseilleviruses have ≈250-nm-large icosahedral capsids and 346–386-kb-long mosaic genomes that encode 444–497 predicted proteins. They share a small set of core genes with Mimivirus and other large and giant DNA viruses that compose a monophyletic group, first described in 2001. Comparative genomics analyses indicate that the family Marseilleviridae currently includes three lineages and a pan-genome composed of ≈600 genes. Antibodies against marseilleviruses and viral DNA have been observed in a significant proportion of asymptomatic individuals and in the blood and lymph nodes of a child with adenitis; these observations suggest that these giant viruses may be blood borne and question if they may be pathogenic in humans.
Virophages are a unique group of circular double-stranded DNA viruses that are considered parasites of giant DNA viruses, which in turn are known to infect eukaryotic hosts. In this study, the genomes of three novel Yellowstone Lake virophages (YSLVs)—YSLV5, YSLV6, and YSLV7—were identified from Yellowstone Lake through metagenomic analyses. The relative abundance of these three novel virophages and previously identified Yellowstone Lake virophages YSLV1 to -4 were determined in different locations of the lake, revealing that most of the sampled locations in the lake, including both mesophilic and thermophilic habitats, had multiple virophage genotypes. This likely reflects the diverse habitats or diversity of the eukaryotic hosts and their associated giant viruses that serve as putative hosts for these virophages. YSLV5 has a 29,767-bp genome with 32 predicted open reading frames (ORFs), YSLV6 has a 24,837-bp genome with 29 predicted ORFs, and YSLV7 has a 23,193-bp genome with 26 predicted ORFs. Based on multilocus phylogenetic analysis, YSLV6 shows a close evolutionary relationship with YSLV1 to -4, whereas YSLV5 and YSLV7 are distantly related to the others, and YSLV7 represents the fourth novel virophage lineage. In addition, the genome of YSLV5 has a G+C content of 51.1% that is much higher than all other known virophages, indicating a unique host range for YSLV5. These results suggest that virophages are abundant and have diverse genotypes that likely mirror diverse giant viral and eukaryotic hosts within the Yellowstone Lake ecosystem.
Marine photosynthesis is one of the major contributors to the global carbon cycle and the world’s oxygen supply. This process is largely driven by cyanobacteria, namely Synechococcus and Prochlorococcus. Genes encoding photosystem-II (PSII) reaction center proteins are found in many cyanophage genomes, and are expressed during the infection of their hosts. On the basis of metagenomics, cyanophage photosystem-I (PSI) gene cassettes were recently discovered with two gene arrangements psaJFCABKED and psaDCAB. It was suggested that the horizontal transfer of PSII and PSI genes is increasing phage fitness. To better understand their diversity, we designed degenerate primers to cover a wide diversity of organisms, and using PCR we targeted the psaCA arrangement, which is unique to cyanophages cassettes. We examined viral concentrates from four islands in the Pacific Ocean and found samples containing the psaCA arrangement. Analyses of the amplified viral psaA gene revealed six subgroups varying in their level of similarity and %G+C content, suggesting that the diversity of cyanophage PSI genes is greater than originally thought.
Knowledge of ancient viruses is limited due to their low concentration and poor preservation in ancient specimens. Using a viral particle-associated nucleic acid enrichment approach, we genetically characterized one complete DNA and one partial RNA viral genome from a 700-y-old fecal sample preserved in ice. Using reverse genetics, we reconstituted the DNA virus, which replicated and systemically spread in a model plant species. Under constant freezing conditions, encapsidated viral nucleic acids may therefore be preserved for centuries. Our finding indicates that cryogenically preserved materials can be repositories of ancient viral nucleic acids, which in turn allow molecular genetics to regenerate viruses to study their biology
By some estimates, almost half of the world's organic carbon is fixed by marine organisms called phytoplankton -- single-celled photosynthetic organisms that account for less than one percent of the total photosynthetic biomass on Earth. When giant algal blooms get viral infections, global carbon cycles are affected, scientists have now discovered.
Seals Can Spread Avian Flu to People Environment News Service WASHINGTON, DC, September 3, 2014 (ENS) – The avian flu virus that caused widespread harbor seal deaths in 2011 can spread to and infect other mammals and potentially humans, new...
Ed Rybicki's insight:
Right up there with "Ebola is airborne!" if you ask me, but still....
Viruses modulate microbial communities and alter ecosystem functions. However, due to cultivation bottlenecks specific virus-host interaction dynamics remain cryptic. Here we examined 127 single-cell amplified genomes (SAGs) from uncultivated SUP05 bacteria isolated from a marine oxygen minimum zone (OMZ) to identify 69 viral contigs representing five new genera within dsDNACaudoviralesand ssDNAMicroviridae. Infection frequencies suggest that ~1/3 of SUP05 bacteria are viral-infected, with higher infection frequency where oxygen-deficiency was most severe. ObservedMicroviridaeclonality suggests recovery of bloom-terminating viruses, while systematic co-infection between dsDNA and ssDNA viruses posits previously unrecognized cooperation modes. Analyses of 186 microbial and viral metagenomes revealed that SUP05 viruses persisted for years, but remained endemic to the OMZ. Finally, identification of virus-encoded dissimilatory sulfite reductase suggests SUP05 viruses reprogram their host's energy metabolism. Together these results demonstrate closely coupled SUP05 virus-host co-evolutionary dynamics with potential to modulate biogeochemical cycling in climate-critical and expanding OMZs.
To celebrate a century of phage exploration, we invite you to get intimate with 30 diverse phages in this premier phage field guide. In these 404 pages you'll learn who these phages are, where on Earth they've been found, who their close relatives are, how their genomes are structured, and how they trick their hosts into submission. Researchers who have devoted their lives to phage also recount their experiences in pursuit of their quarry.
Ed Rybicki's insight:
WHAT a good idea - in our continuing celebration of The Centenary of the Phage. Thanks Zwirko!
Viruses affect biogeochemical cycling, microbial mortality, gene flow, and metabolic functions in diverse environments through infection and lysis of microorganisms. Fundamental to quantitatively investigating these roles is the determination of viral abundance in both field and laboratory samples. One current, widely-used method to accomplish this in aquatic samples is the ‘filter-mount’ method in which samples are filtered onto costly 0.02 μm-pore-size ceramic filters for enumeration of viruses with epifluorescence microscopy. Here we describe a cost-effective (ca. 500-fold lower materials cost) alternative virus enumeration method in which fluorescently-stained samples are wet-mounted directly onto slides, after optional chemical flocculation of viruses in samples with viral concentrations <5×107 mL-1. The concentration of viruses in the sample is then determined from the ratio of viruses to a known concentration of added microsphere beads via epifluorescence microscopy. Virus concentrations obtained using this wet-mount method, with and without chemical flocculation, were significantly correlated with, and had equivalent precision to, those from the filter-mount method across concentrations ranging from 2.17×106 to 1.37×108 viruses mL-1 when tested using cultivated viral isolates and natural samples from marine and freshwater environments. In summary, the wet-mount method is significantly less expensive than the filter-mount method, and is appropriate for rapid, precise and accurate enumeration of aquatic viruses over a wide range of viral concentrations (≥1×106 viruses mL-1) encountered in field and laboratory samples.
Marine viruses have important roles in microbial mortality, gene transfer, metabolic reprogramming and biogeochemical cycling. In this Review, we discuss recent technological advances in marine virology including the use of near-quantitative, reproducible metagenomics for large-scale investigation of viral communities and the emergence of gene-based viral ecology. We also describe the reprogramming of microbially driven processes by viral metabolic genes, the identification of novel viruses using cultivation-dependent and cultivation-independent tools, and the potential for modelling studies to provide a framework for studying virus–host interactions. These transformative advances have set a rapid pace in exploring and predicting how marine viruses manipulate and respond to their environment.
Ed Rybicki's insight:
Excellent stuff!! I have been fascinated by this field for years; I only hope we can stay in it a while.
In the environment, protozoa are predators of bacteria and feed on them. The possibility that some protozoa could be a source of human pathogens is consistent with the discovery that free-living amoebae were the reservoir of Legionella pneumophila, the agent of Legionnaires' disease. Later, while searching for Legionella in the environment using amoeba co-culture, the first giant virus, Acanthamoeba polyphaga mimivirus, was discovered. Since then, many other giant viruses have been isolated, includingMarseilleviridae, Pithovirus sibericum, Cafeteria roenbergensis virus and Pandoravirus spp. The methods used to isolate all of these viruses are herein reviewed. By analogy to Legionella, it was originally suspected that these viruses could be human pathogens. After showing by indirect evidence, such as sero-epidemiologic studies, that it was possible for these viruses to be human pathogens, the recent isolation of some of these viruses (belonging to the Mimiviridae and Marseilleviridae families) in humans in the context of pathologic conditions shows that they are opportunistic human pathogens in some instances.
Mimivirus picture courtesy of Russell Kightley Media
We have isolated three novel lytic dsDNA-viruses from Raunefjorden (Norway) that are putative members of the Mimiviridae family, namely Haptolina ericina virus RF02 (HeV RF02), Prymnesium kappa virus RF01 (PkV RF01), and Prymnesium kappa virus RF02 (PkV RF02). Each of the novel haptophyte viruses challenges the common conceptions of algal viruses with respect to host range, phylogenetic affiliation and size. PkV RF01 has a capsid of ~310 nm and is the largest algal virus particle ever reported while PkV RF01 and HeV RF02 were able to infect different species, even belonging to different genera. Moreover, PkV RF01 and HeV RF02 infected the same hosts, but phylogenetic analysis placed them in different groups. Our results reveal large variation among viruses infecting closely related microalgae, and challenge the common conception that algal viruses have narrow host range, and phylogeny reflecting their host affiliation.
Human mucosal surfaces contain a wide range of microorganisms. The biological effects of these organisms are largely unknown. Large-scale metagenomic sequencing is emerging as a method to identify novel microbes. Unexpectedly, we identified DNA sequences homologous to virus ATCV-1, an algal virus not previously known to infect humans, in oropharyngeal samples obtained from healthy adults. The presence of ATCV-1 was associated with a modest but measurable decrease in cognitive functioning. A relationship between ATCV-1 and cognitive functioning was confirmed in a mouse model, which also indicated that exposure to ATCV-1 resulted in changes in gene expression within the brain. Our study indicates that viruses in the environment not thought to infect humans can have biological effects.
Marine microorganisms constitute the largest percentage of living biomass and serve as the major driving force behind nutrient and energy cycles. While viruses only comprise a small percentage of this biomass (i.e., 5%), they dominate in numerical abundance and genetic diversity. Through host infection and mortality, viruses affect microbial population dynamics, community composition, genetic evolution, and biogeochemical cycling. However, the field of marine viral ecology is currently limited by a lack of data regarding how different environmental factors regulate virus dynamics and host–virus interactions. The goal of the present minireview was to contribute to the evolution of marine viral ecology, through the assimilation of available data regarding the manner and degree to which environmental factors affect viral decay and infectivity as well as influence latent period and production. Considering the ecological importance of viruses in the marine ecosystem and the increasing pressure from anthropogenic activity and global climate change on marine systems, a synthesis of existing information provides a timely framework for future research initiatives in viral ecology.
Marine mutants wash up on shore: two-headed dolphin a sign of chemical poisoning tipping point (Marine mutants wash up on shore: two-headed dolphin a sign of chemical poisoning tipping point http://t.co/4c0zQooEOH)...
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