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Special Issue "Marine Viruses 2016"

A special issue of Viruses (ISSN 1999-4915). This special issue belongs to the section "Animal Viruses".

Deadline for manuscript submissions: closed (31 January 2017)

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Guest Editor
Prof. Mathias Middelboe

Marine Biological Section, University of Copenhagen, Copenhagen, Denmark
Website | E-Mail
Interests: marine viral ecology; phage-host interactions
Guest Editor
Prof. Dr. Corina P.D. Brussaard

Department of Marine Microbiology and Biogeoxhemistry, NIOZ - Royal Netherlands Institute for Sea Research, 1790 AB Den Burg, Texel, The Netherlands & Institute for Biodiversity and Ecosystem Dynamics (IBED) at Univ. Amsterdam, The Netherlands
Website | E-Mail
Interests: Aquatic viral ecology, Marine microbiology, mortality, phytoplankton-host interactions

Special Issue Information

Dear Colleagues,

The research effort, publication rate and scientific community within the field of marine viruses have been growing rapidly the past decade and viruses are now known to play key roles in microbial population dynamics, diversity and evolution as well as biogeochemical cycling.

The aim of this special issue is to highlight the progress in our understanding of the role of viruses in the marine environment by presenting novel research on the ecology, distribution and diversity of marine viruses and the influence of virus-host interactions on e.g. mortality, element cycling and evolution of marine microbial communities.  

Prof. Mathias Middelboe
Prof. Dr. Corina:P.D. Brussaard
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Viruses is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Virus-host interactions
  • marine viral ecology
  • virus diversity
  • prophages
  • virus-driven evolution
  • viral genomics and metagenomics

Published Papers (20 papers)

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Editorial

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Open AccessEditorial
Marine Viruses: Key Players in Marine Ecosystems
Viruses 2017, 9(10), 302; https://doi.org/10.3390/v9100302
Received: 12 October 2017 / Accepted: 16 October 2017 / Published: 18 October 2017
Cited by 8 | PDF Full-text (1075 KB) | HTML Full-text | XML Full-text
Abstract
Viruses were recognized as the causative agents of fish diseases, such as infectious pancreatic necrosis and Oregon sockeye disease, in the early 1960s [1], and have since been shown to be responsible for diseases in all marine life from bacteria to protists, mollusks, [...] Read more.
Viruses were recognized as the causative agents of fish diseases, such as infectious pancreatic necrosis and Oregon sockeye disease, in the early 1960s [1], and have since been shown to be responsible for diseases in all marine life from bacteria to protists, mollusks, crustaceans, fish and mammals [2].[...] Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Research

Jump to: Editorial, Review, Other

Open AccessArticle
The Response of Heterotrophic Prokaryote and Viral Communities to Labile Organic Carbon Inputs Is Controlled by the Predator Food Chain Structure
Viruses 2017, 9(9), 238; https://doi.org/10.3390/v9090238
Received: 27 June 2017 / Revised: 4 August 2017 / Accepted: 17 August 2017 / Published: 23 August 2017
Cited by 5 | PDF Full-text (2218 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Factors controlling the community composition of marine heterotrophic prokaryotes include organic-C, mineral nutrients, predation, and viral lysis. Two mesocosm experiments, performed at an Arctic location and bottom-up manipulated with organic-C, had very different results in community composition for both prokaryotes and viruses. Previously, [...] Read more.
Factors controlling the community composition of marine heterotrophic prokaryotes include organic-C, mineral nutrients, predation, and viral lysis. Two mesocosm experiments, performed at an Arctic location and bottom-up manipulated with organic-C, had very different results in community composition for both prokaryotes and viruses. Previously, we showed how a simple mathematical model could reproduce food web level dynamics observed in these mesocosms, demonstrating strong top-down control through the predator chain from copepods via ciliates and heterotrophic nanoflagellates. Here, we use a steady-state analysis to connect ciliate biomass to bacterial carbon demand. This gives a coupling of top-down and bottom-up factors whereby low initial densities of ciliates are associated with mineral nutrient-limited heterotrophic prokaryotes that do not respond to external supply of labile organic-C. In contrast, high initial densities of ciliates give carbon-limited growth and high responsiveness to organic-C. The differences observed in ciliate abundance, and in prokaryote abundance and community composition in the two experiments were in accordance with these predictions. Responsiveness in the viral community followed a pattern similar to that of prokaryotes. Our study provides a unique link between the structure of the predator chain in the microbial food web and viral abundance and diversity. Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessArticle
Nutrients and Other Environmental Factors Influence Virus Abundances across Oxic and Hypoxic Marine Environments
Viruses 2017, 9(6), 152; https://doi.org/10.3390/v9060152
Received: 15 March 2017 / Revised: 10 June 2017 / Accepted: 13 June 2017 / Published: 17 June 2017
Cited by 12 | PDF Full-text (1224 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Virus particles are highly abundant in seawater and, on average, outnumber microbial cells approximately 10-fold at the surface and 16-fold in deeper waters; yet, this relationship varies across environments. Here, we examine the influence of a suite of environmental variables, including nutrient concentrations, [...] Read more.
Virus particles are highly abundant in seawater and, on average, outnumber microbial cells approximately 10-fold at the surface and 16-fold in deeper waters; yet, this relationship varies across environments. Here, we examine the influence of a suite of environmental variables, including nutrient concentrations, salinity and temperature, on the relationship between the abundances of viruses and prokaryotes over a broad range of spatial and temporal scales, including along a track from the Northwest Atlantic to the Northeast Pacific via the Arctic Ocean, and in the coastal waters of British Columbia, Canada. Models of varying complexity were tested and compared for best fit with the Akaike Information Criterion, and revealed that nitrogen and phosphorus concentrations, as well as prokaryote abundances, either individually or combined, had significant effects on viral abundances in all but hypoxic environments, which were only explained by a combination of physical and chemical factors. Nonetheless, multivariate models of environmental variables showed high explanatory power, matching or surpassing that of prokaryote abundance alone. Incorporating both environmental variables and prokaryote abundances into multivariate models significantly improved the explanatory power of the models, except in hypoxic environments. These findings demonstrate that environmental factors could be as important as, or even more important than, prokaryote abundance in describing viral abundance across wide-ranging marine environments Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessArticle
Two Synechococcus genes, Two Different Effects on Cyanophage Infection
Viruses 2017, 9(6), 136; https://doi.org/10.3390/v9060136
Received: 7 April 2017 / Revised: 22 May 2017 / Accepted: 23 May 2017 / Published: 2 June 2017
Cited by 2 | PDF Full-text (1448 KB) | HTML Full-text | XML Full-text
Abstract
Synechococcus is an abundant marine cyanobacterium that significantly contributes to primary production. Lytic phages are thought to have a major impact on cyanobacterial population dynamics and evolution. Previously, an investigation of the transcriptional response of three Synechococcus strains to infection by the T4-like [...] Read more.
Synechococcus is an abundant marine cyanobacterium that significantly contributes to primary production. Lytic phages are thought to have a major impact on cyanobacterial population dynamics and evolution. Previously, an investigation of the transcriptional response of three Synechococcus strains to infection by the T4-like cyanomyovirus, Syn9, revealed that while the transcript levels of the vast majority of host genes declined soon after infection, those for some genes increased or remained stable. In order to assess the role of two such host-response genes during infection, we inactivated them in Synechococcus sp. strain WH8102. One gene, SYNW1659, encodes a domain of unknown function (DUF3387) that is associated with restriction enzymes. The second gene, SYNW1946, encodes a PIN-PhoH protein, of which the PIN domain is common in bacterial toxin-antitoxin systems. Neither of the inactivation mutations impacted host growth or the length of the Syn9 lytic cycle. However, the DUF3387 mutant supported significantly lower phage DNA replication and yield of phage progeny than the wild-type, suggesting that the product of this host gene aids phage production. The PIN-PhoH mutant, on the other hand, allowed for significantly higher Syn9 genomic DNA replication and progeny production, suggesting that this host gene plays a role in restraining the infection process. Our findings indicate that host-response genes play a functional role during infection and suggest that some function in an attempt at defense against the phage, while others are exploited by the phage for improved infection. Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessArticle
Characterization and Temperature Dependence of Arctic Micromonas polaris Viruses
Viruses 2017, 9(6), 134; https://doi.org/10.3390/v9060134
Received: 4 March 2017 / Revised: 24 May 2017 / Accepted: 25 May 2017 / Published: 2 June 2017
Cited by 8 | PDF Full-text (4236 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Global climate change-induced warming of the Artic seas is predicted to shift the phytoplankton community towards dominance of smaller-sized species due to global warming. Yet, little is known about their viral mortality agents despite the ecological importance of viruses regulating phytoplankton host dynamics [...] Read more.
Global climate change-induced warming of the Artic seas is predicted to shift the phytoplankton community towards dominance of smaller-sized species due to global warming. Yet, little is known about their viral mortality agents despite the ecological importance of viruses regulating phytoplankton host dynamics and diversity. Here we report the isolation and basic characterization of four prasinoviruses infectious to the common Arctic picophytoplankter Micromonas. We furthermore assessed how temperature influenced viral infectivity and production. Phylogenetic analysis indicated that the putative double-stranded DNA (dsDNA) Micromonas polaris viruses (MpoVs) are prasinoviruses (Phycodnaviridae) of approximately 120 nm in particle size. One MpoV showed intrinsic differences to the other three viruses, i.e., larger genome size (205 ± 2 vs. 191 ± 3 Kb), broader host range, and longer latent period (39 vs. 18 h). Temperature increase shortened the latent periods (up to 50%), increased the burst size (up to 40%), and affected viral infectivity. However, the variability in response to temperature was high for the different viruses and host strains assessed, likely affecting the Arctic picoeukaryote community structure both in the short term (seasonal cycles) and long term (global warming). Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessArticle
Stumbling across the Same Phage: Comparative Genomics of Widespread Temperate Phages Infecting the Fish Pathogen Vibrio anguillarum
Viruses 2017, 9(5), 122; https://doi.org/10.3390/v9050122
Received: 1 March 2017 / Revised: 12 May 2017 / Accepted: 12 May 2017 / Published: 20 May 2017
Cited by 10 | PDF Full-text (2622 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Nineteen Vibrio anguillarum-specific temperate bacteriophages isolated across Europe and Chile from aquaculture and environmental sites were genome sequenced and analyzed for host range, morphology and life cycle characteristics. The phages were classified as Siphoviridae with genome sizes between 46,006 and 54,201 bp. [...] Read more.
Nineteen Vibrio anguillarum-specific temperate bacteriophages isolated across Europe and Chile from aquaculture and environmental sites were genome sequenced and analyzed for host range, morphology and life cycle characteristics. The phages were classified as Siphoviridae with genome sizes between 46,006 and 54,201 bp. All 19 phages showed high genetic similarity, and 13 phages were genetically identical. Apart from sporadically distributed single nucleotide polymorphisms (SNPs), genetic diversifications were located in three variable regions (VR1, VR2 and VR3) in six of the phage genomes. Identification of specific genes, such as N6-adenine methyltransferase and lambda like repressor, as well as the presence of a tRNAArg, suggested a both mutualistic and parasitic interaction between phages and hosts. During short term phage exposure experiments, 28% of a V. anguillarum host population was lysogenized by the temperate phages and a genomic analysis of a collection of 31 virulent V. anguillarum showed that the isolated phages were present as prophages in >50% of the strains covering large geographical distances. Further, phage sequences were widely distributed among CRISPR-Cas arrays of publicly available sequenced Vibrios. The observed distribution of these specific temperate Vibriophages across large geographical scales may be explained by efficient dispersal of phages and bacteria in the marine environment combined with a mutualistic interaction between temperate phages and their hosts which selects for co-existence rather than arms race dynamics. Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessArticle
A Novel Roseosiphophage Isolated from the Oligotrophic South China Sea
Viruses 2017, 9(5), 109; https://doi.org/10.3390/v9050109
Received: 28 February 2017 / Revised: 22 April 2017 / Accepted: 10 May 2017 / Published: 15 May 2017
Cited by 8 | PDF Full-text (3344 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The Roseobacter clade is abundant and widespread in marine environments and plays an important role in oceanic biogeochemical cycling. In this present study, a lytic siphophage (labeled vB_DshS-R5C) infecting the strain type of Dinoroseobacter shibae named DFL12T, which is part of [...] Read more.
The Roseobacter clade is abundant and widespread in marine environments and plays an important role in oceanic biogeochemical cycling. In this present study, a lytic siphophage (labeled vB_DshS-R5C) infecting the strain type of Dinoroseobacter shibae named DFL12T, which is part of the Roseobacter clade, was isolated from the oligotrophic South China Sea. Phage R5C showed a narrow host range, short latent period and low burst size. The genome length of phage R5C was 77, 874 bp with a G+C content of 61.5%. Genomic comparisons detected no genome matches in the GenBank database and phylogenetic analysis based on DNA polymerase I revealed phylogenetic features that were distinct to other phages, suggesting the novelty of R5C. Several auxiliary metabolic genes (e.g., phoH gene, heat shock protein and queuosine biosynthesis genes) were identified in the R5C genome that may be beneficial to the host and/or offer a competitive advantage for the phage. Among siphophages infecting the Roseobacter clade (roseosiphophages), four gene transfer agent-like genes were commonly located with close proximity to structural genes, suggesting that their function may be related to the tail of siphoviruses. The isolation and characterization of R5C demonstrated the high genomic and physiological diversity of roseophages as well as improved our understanding of host–phage interactions and the ecology of the marine Roseobacter. Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessArticle
Seasonal Dynamics of Haptophytes and dsDNA Algal Viruses Suggest Complex Virus-Host Relationship
Viruses 2017, 9(4), 84; https://doi.org/10.3390/v9040084
Received: 31 January 2017 / Revised: 6 April 2017 / Accepted: 13 April 2017 / Published: 20 April 2017
Cited by 6 | PDF Full-text (1942 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Viruses influence the ecology and diversity of phytoplankton in the ocean. Most studies of phytoplankton host–virus interactions have focused on bloom-forming species like Emiliania huxleyi or Phaeocystis spp. The role of viruses infecting phytoplankton that do not form conspicuous blooms have received less [...] Read more.
Viruses influence the ecology and diversity of phytoplankton in the ocean. Most studies of phytoplankton host–virus interactions have focused on bloom-forming species like Emiliania huxleyi or Phaeocystis spp. The role of viruses infecting phytoplankton that do not form conspicuous blooms have received less attention. Here we explore the dynamics of phytoplankton and algal viruses over several sequential seasons, with a focus on the ubiquitous and diverse phytoplankton division Haptophyta, and their double-stranded DNA viruses, potentially with the capacity to infect the haptophytes. Viral and phytoplankton abundance and diversity showed recurrent seasonal changes, mainly explained by hydrographic conditions. By 454 tag-sequencing we revealed 93 unique haptophyte operational taxonomic units (OTUs), with seasonal changes in abundance. Sixty-one unique viral OTUs, representing Megaviridae and Phycodnaviridae, showed only distant relationship with currently isolated algal viruses. Haptophyte and virus community composition and diversity varied substantially throughout the year, but in an uncoordinated manner. A minority of the viral OTUs were highly abundant at specific time-points, indicating a boom-bust relationship with their host. Most of the viral OTUs were very persistent, which may represent viruses that coexist with their hosts, or able to exploit several host species. Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessArticle
Emerging Interaction Patterns in the Emiliania huxleyi-EhV System
Viruses 2017, 9(3), 61; https://doi.org/10.3390/v9030061
Received: 30 January 2017 / Revised: 15 March 2017 / Accepted: 16 March 2017 / Published: 22 March 2017
Cited by 3 | PDF Full-text (1812 KB) | HTML Full-text | XML Full-text | Correction
Abstract
Viruses are thought to be fundamental in driving microbial diversity in the oceanic planktonic realm. That role and associated emerging infection patterns remain particularly elusive for eukaryotic phytoplankton and their viruses. Here we used a vast number of strains from the model system [...] Read more.
Viruses are thought to be fundamental in driving microbial diversity in the oceanic planktonic realm. That role and associated emerging infection patterns remain particularly elusive for eukaryotic phytoplankton and their viruses. Here we used a vast number of strains from the model system Emiliania huxleyi/Emiliania huxleyi Virus to quantify parameters such as growth rate (µ), resistance (R), and viral production (Vp) capacities. Algal and viral abundances were monitored by flow cytometry during 72-h incubation experiments. The results pointed out higher viral production capacity in generalist EhV strains, and the virus-host infection network showed a strong co-evolution pattern between E. huxleyi and EhV populations. The existence of a trade-off between resistance and growth capacities was not confirmed. Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessArticle
Isolation and Characterization of a Shewanella Phage–Host System from the Gut of the Tunicate, Ciona intestinalis
Viruses 2017, 9(3), 60; https://doi.org/10.3390/v9030060
Received: 29 January 2017 / Revised: 8 March 2017 / Accepted: 17 March 2017 / Published: 22 March 2017
Cited by 5 | PDF Full-text (3779 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Outnumbering all other biological entities on earth, bacteriophages (phages) play critical roles in structuring microbial communities through bacterial infection and subsequent lysis, as well as through horizontal gene transfer. While numerous studies have examined the effects of phages on free-living bacterial cells, much [...] Read more.
Outnumbering all other biological entities on earth, bacteriophages (phages) play critical roles in structuring microbial communities through bacterial infection and subsequent lysis, as well as through horizontal gene transfer. While numerous studies have examined the effects of phages on free-living bacterial cells, much less is known regarding the role of phage infection in host-associated biofilms, which help to stabilize adherent microbial communities. Here we report the cultivation and characterization of a novel strain of Shewanella fidelis from the gut of the marine tunicate Ciona intestinalis, inducible prophages from the S. fidelis genome, and a strain-specific lytic phage recovered from surrounding seawater. In vitro biofilm assays demonstrated that lytic phage infection affects biofilm formation in a process likely influenced by the accumulation and integration of the extracellular DNA released during cell lysis, similar to the mechanism that has been previously shown for prophage induction. Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessFeature PaperArticle
Coccolithoviruses: A Review of Cross-Kingdom Genomic Thievery and Metabolic Thuggery
Viruses 2017, 9(3), 52; https://doi.org/10.3390/v9030052
Received: 18 January 2017 / Revised: 13 March 2017 / Accepted: 14 March 2017 / Published: 18 March 2017
Cited by 9 | PDF Full-text (5240 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Coccolithoviruses (Phycodnaviridae) infect and lyse the most ubiquitous and successful coccolithophorid in modern oceans, Emiliania huxleyi. So far, the genomes of 13 of these giant lytic viruses (i.e., Emiliania huxleyi viruses—EhVs) have been sequenced, assembled, and annotated. Here, we performed [...] Read more.
Coccolithoviruses (Phycodnaviridae) infect and lyse the most ubiquitous and successful coccolithophorid in modern oceans, Emiliania huxleyi. So far, the genomes of 13 of these giant lytic viruses (i.e., Emiliania huxleyi viruses—EhVs) have been sequenced, assembled, and annotated. Here, we performed an in-depth comparison of their genomes to try and contextualize the ecological and evolutionary traits of these viruses. The genomes of these EhVs have from 444 to 548 coding sequences (CDSs). Presence/absence analysis of CDSs identified putative genes with particular ecological significance, namely sialidase, phosphate permease, and sphingolipid biosynthesis. The viruses clustered into distinct clades, based on their DNA polymerase gene as well as full genome comparisons. We discuss the use of such clustering and suggest that a gene-by-gene investigation approach may be more useful when the goal is to reveal differences related to functionally important genes. A multi domain “Best BLAST hit” analysis revealed that 84% of the EhV genes have closer similarities to the domain Eukarya. However, 16% of the EhV CDSs were very similar to bacterial genes, contributing to the idea that a significant portion of the gene flow in the planktonic world inter-crosses the domains of life. Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessArticle
Schrödinger’s Cheshire Cat: Are Haploid Emiliania huxleyi Cells Resistant to Viral Infection or Not?
Viruses 2017, 9(3), 51; https://doi.org/10.3390/v9030051
Received: 31 January 2017 / Revised: 10 March 2017 / Accepted: 14 March 2017 / Published: 18 March 2017
Cited by 3 | PDF Full-text (4513 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Emiliania huxleyi is the main calcite producer on Earth and is routinely infected by a virus (EhV); a double stranded DNA (dsDNA) virus belonging to the family Phycodnaviridae. E. huxleyi exhibits a haplodiploid life cycle; the calcified diploid stage is non-motile and [...] Read more.
Emiliania huxleyi is the main calcite producer on Earth and is routinely infected by a virus (EhV); a double stranded DNA (dsDNA) virus belonging to the family Phycodnaviridae. E. huxleyi exhibits a haplodiploid life cycle; the calcified diploid stage is non-motile and forms extensive blooms. The haploid phase is a non-calcified biflagellated cell bearing organic scales. Haploid cells are thought to resist infection, through a process deemed the “Cheshire Cat” escape strategy; however, a recent study detected the presence of viral lipids in the same haploid strain. Here we report on the application of an E. huxleyi CCMP1516 EhV-86 combined tiling array (TA) that further confirms an EhV infection in the RCC1217 haploid strain, which grew without any signs of cell lysis. Reverse transcription polymerase chain reaction (RT-PCR) and PCR verified the presence of viral RNA in the haploid cells, yet indicated an absence of viral DNA, respectively. These infected cells are an alternative stage of the virus life cycle deemed the haplococcolithovirocell. In this instance, the host is both resistant to and infected by EhV, i.e., the viral transcriptome is present in haploid cells whilst there is no evidence of viral lysis. This superimposed state is reminiscent of Schrödinger’s cat; of being simultaneously both dead and alive. Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessArticle
Viral Protein Kinetics of Piscine Orthoreovirus Infection in Atlantic Salmon Blood Cells
Viruses 2017, 9(3), 49; https://doi.org/10.3390/v9030049
Received: 15 December 2016 / Revised: 7 March 2017 / Accepted: 10 March 2017 / Published: 18 March 2017
Cited by 15 | PDF Full-text (11959 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Piscine orthoreovirus (PRV) is ubiquitous in farmed Atlantic salmon (Salmo salar) and the cause of heart and skeletal muscle inflammation. Erythrocytes are important target cells for PRV. We have investigated the kinetics of PRV infection in salmon blood cells. The findings [...] Read more.
Piscine orthoreovirus (PRV) is ubiquitous in farmed Atlantic salmon (Salmo salar) and the cause of heart and skeletal muscle inflammation. Erythrocytes are important target cells for PRV. We have investigated the kinetics of PRV infection in salmon blood cells. The findings indicate that PRV causes an acute infection of blood cells lasting 1–2 weeks, before it subsides into persistence. A high production of viral proteins occurred initially in the acute phase which significantly correlated with antiviral gene transcription. Globular viral factories organized by the non-structural protein µNS were also observed initially, but were not evident at later stages. Interactions between µNS and the PRV structural proteins λ1, µ1, σ1 and σ3 were demonstrated. Different size variants of µNS and the outer capsid protein µ1 appeared at specific time points during infection. Maximal viral protein load was observed five weeks post cohabitant challenge and was undetectable from seven weeks post challenge. In contrast, viral RNA at a high level could be detected throughout the eight-week trial. A proteolytic cleavage fragment of the µ1 protein was the only viral protein detectable after seven weeks post challenge, indicating that this µ1 fragment may be involved in the mechanisms of persistent infection. Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessArticle
A Pelagic Microbiome (Viruses to Protists) from a Small Cup of Seawater
Viruses 2017, 9(3), 47; https://doi.org/10.3390/v9030047
Received: 13 January 2017 / Revised: 13 March 2017 / Accepted: 13 March 2017 / Published: 17 March 2017
Cited by 4 | PDF Full-text (5565 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The aquatic microbiome is composed of a multi-phylotype community of microbes, ranging from the numerically dominant viruses to the phylogenetically diverse unicellular phytoplankton. They influence key biogeochemical processes and form the base of marine food webs, becoming food for secondary consumers. Due to [...] Read more.
The aquatic microbiome is composed of a multi-phylotype community of microbes, ranging from the numerically dominant viruses to the phylogenetically diverse unicellular phytoplankton. They influence key biogeochemical processes and form the base of marine food webs, becoming food for secondary consumers. Due to recent advances in next-generation sequencing, this previously overlooked component of our hydrosphere is starting to reveal its true diversity and biological complexity. We report here that 250 mL of seawater is sufficient to provide a comprehensive description of the microbial diversity in an oceanic environment. We found that there was a dominance of the order Caudovirales (59%), with the family Myoviridae being the most prevalent. The families Phycodnaviridae and Mimiviridae made up the remainder of pelagic double-stranded DNA (dsDNA) virome. Consistent with this analysis, the Cyanobacteria dominate (52%) the prokaryotic diversity. While the dinoflagellates and their endosymbionts, the superphylum Alveolata dominates (92%) the microbial eukaryotic diversity. A total of 834 prokaryotic, 346 eukaryotic and 254 unique virus phylotypes were recorded in this relatively small sample of water. We also provide evidence, through a metagenomic-barcoding comparative analysis, that viruses are the likely source of microbial environmental DNA (meDNA). This study opens the door to a more integrated approach to oceanographic sampling and data analysis. Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessArticle
Isolation and Characterization of a Double Stranded DNA Megavirus Infecting the Toxin-Producing Haptophyte Prymnesium parvum
Viruses 2017, 9(3), 40; https://doi.org/10.3390/v9030040
Received: 29 January 2017 / Revised: 22 February 2017 / Accepted: 27 February 2017 / Published: 9 March 2017
Cited by 8 | PDF Full-text (1704 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Prymnesium parvum is a toxin-producing haptophyte that causes harmful algal blooms globally, leading to large-scale fish kills that have severe ecological and economic implications. For the model haptophyte, Emiliania huxleyi, it has been shown that large dsDNA viruses play an important role [...] Read more.
Prymnesium parvum is a toxin-producing haptophyte that causes harmful algal blooms globally, leading to large-scale fish kills that have severe ecological and economic implications. For the model haptophyte, Emiliania huxleyi, it has been shown that large dsDNA viruses play an important role in regulating blooms and therefore biogeochemical cycling, but much less work has been done looking at viruses that infect P. parvum, or the role that these viruses may play in regulating harmful algal blooms. In this study, we report the isolation and characterization of a lytic nucleo-cytoplasmic large DNA virus (NCLDV) collected from the site of a harmful P. parvum bloom. In subsequent experiments, this virus was shown to infect cultures of Prymnesium sp. and showed phylogenetic similarity to the extended Megaviridae family of algal viruses. Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessArticle
Change in Emiliania huxleyi Virus Assemblage Diversity but Not in Host Genetic Composition during an Ocean Acidification Mesocosm Experiment
Viruses 2017, 9(3), 41; https://doi.org/10.3390/v9030041
Received: 12 January 2017 / Revised: 23 February 2017 / Accepted: 2 March 2017 / Published: 8 March 2017
Cited by 2 | PDF Full-text (5590 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Effects of elevated pCO2 on Emiliania huxleyi genetic diversity and the viruses that infect E. huxleyi (EhVs) have been investigated in large volume enclosures in a Norwegian fjord. Triplicate enclosures were bubbled with air enriched with CO2 to 760 ppmv [...] Read more.
Effects of elevated pCO2 on Emiliania huxleyi genetic diversity and the viruses that infect E. huxleyi (EhVs) have been investigated in large volume enclosures in a Norwegian fjord. Triplicate enclosures were bubbled with air enriched with CO2 to 760 ppmv whilst the other three enclosures were bubbled with air at ambient pCO2; phytoplankton growth was initiated by the addition of nitrate and phosphate. E. huxleyi was the dominant coccolithophore in all enclosures, but no difference in genetic diversity, based on DGGE analysis using primers specific to the calcium binding protein gene (gpa) were detected in any of the treatments. Chlorophyll concentrations and primary production were lower in the three elevated pCO2 treatments than in the ambient treatments. However, although coccolithophores numbers were reduced in two of the high-pCO2 treatments; in the third, there was no suppression of coccolithophores numbers, which were very similar to the three ambient treatments. In contrast, there was considerable variation in genetic diversity in the EhVs, as determined by analysis of the major capsid protein (mcp) gene. EhV diversity was much lower in the high-pCO2 treatment enclosure that did not show inhibition of E. huxleyi growth. Since virus infection is generally implicated as a major factor in terminating phytoplankton blooms, it is suggested that no study of the effect of ocean acidification in phytoplankton can be complete if it does not include an assessment of viruses. Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessArticle
Virus Resistance Is Not Costly in a Marine Alga Evolving under Multiple Environmental Stressors
Viruses 2017, 9(3), 39; https://doi.org/10.3390/v9030039
Received: 25 January 2017 / Revised: 24 February 2017 / Accepted: 28 February 2017 / Published: 8 March 2017
Cited by 4 | PDF Full-text (1989 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Viruses are important evolutionary drivers of host ecology and evolution. The marine picoplankton Ostreococcus tauri has three known resistance types that arise in response to infection with the Phycodnavirus OtV5: susceptible cells (S) that lyse following viral entry and replication; resistant cells (R) [...] Read more.
Viruses are important evolutionary drivers of host ecology and evolution. The marine picoplankton Ostreococcus tauri has three known resistance types that arise in response to infection with the Phycodnavirus OtV5: susceptible cells (S) that lyse following viral entry and replication; resistant cells (R) that are refractory to viral entry; and resistant producers (RP) that do not all lyse but maintain some viruses within the population. To test for evolutionary costs of maintaining antiviral resistance, we examined whether O. tauri populations composed of each resistance type differed in their evolutionary responses to several environmental drivers (lower light, lower salt, lower phosphate and a changing environment) in the absence of viruses for approximately 200 generations. We did not detect a cost of resistance as measured by life-history traits (population growth rate, cell size and cell chlorophyll content) and competitive ability. Specifically, all R and RP populations remained resistant to OtV5 lysis for the entire 200-generation experiment, whereas lysis occurred in all S populations, suggesting that resistance is not costly to maintain even when direct selection for resistance was removed, or that there could be a genetic constraint preventing return to a susceptible resistance type. Following evolution, all S population densities dropped when inoculated with OtV5, but not to zero, indicating that lysis was incomplete, and that some cells may have gained a resistance mutation over the evolution experiment. These findings suggest that maintaining resistance in the absence of viruses was not costly. Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Review

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Open AccessReview
A Student’s Guide to Giant Viruses Infecting Small Eukaryotes: From Acanthamoeba to Zooxanthellae
Viruses 2017, 9(3), 46; https://doi.org/10.3390/v9030046
Received: 27 December 2016 / Revised: 7 March 2017 / Accepted: 9 March 2017 / Published: 17 March 2017
Cited by 12 | PDF Full-text (1148 KB) | HTML Full-text | XML Full-text
Abstract
The discovery of infectious particles that challenge conventional thoughts concerning “what is a virus” has led to the evolution a new field of study in the past decade. Here, we review knowledge and information concerning “giant viruses”, with a focus not only on [...] Read more.
The discovery of infectious particles that challenge conventional thoughts concerning “what is a virus” has led to the evolution a new field of study in the past decade. Here, we review knowledge and information concerning “giant viruses”, with a focus not only on some of the best studied systems, but also provide an effort to illuminate systems yet to be better resolved. We conclude by demonstrating that there is an abundance of new host–virus systems that fall into this “giant” category, demonstrating that this field of inquiry presents great opportunities for future research. Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessReview
Marine Prasinoviruses and Their Tiny Plankton Hosts: A Review
Viruses 2017, 9(3), 43; https://doi.org/10.3390/v9030043
Received: 31 January 2017 / Revised: 4 March 2017 / Accepted: 8 March 2017 / Published: 15 March 2017
Cited by 7 | PDF Full-text (4697 KB) | HTML Full-text | XML Full-text
Abstract
Viruses play a crucial role in the marine environment, promoting nutrient recycling and biogeochemical cycling and driving evolutionary processes. Tiny marine phytoplankton called prasinophytes are ubiquitous and significant contributors to global primary production and biomass. A number of viruses (known as prasinoviruses) that [...] Read more.
Viruses play a crucial role in the marine environment, promoting nutrient recycling and biogeochemical cycling and driving evolutionary processes. Tiny marine phytoplankton called prasinophytes are ubiquitous and significant contributors to global primary production and biomass. A number of viruses (known as prasinoviruses) that infect these important primary producers have been isolated and characterised over the past decade. Here we review the current body of knowledge about prasinoviruses and their interactions with their algal hosts. Several genes, including those encoding for glycosyltransferases, methyltransferases and amino acid synthesis enzymes, which have never been identified in viruses of eukaryotes previously, have been detected in prasinovirus genomes. The host organisms are also intriguing; most recently, an immunity chromosome used by a prasinophyte in response to viral infection was discovered. In light of such recent, novel discoveries, we discuss why the cellular simplicity of prasinophytes makes for appealing model host organism–virus systems to facilitate focused and detailed investigations into the dynamics of marine viruses and their intimate associations with host species. We encourage the adoption of the prasinophyte Ostreococcus and its associated viruses as a model host–virus system for examination of cellular and molecular processes in the marine environment. Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessCorrection
Correction: Ruiz, E. et al. Emerging Interaction Patterns in the Emiliania Huxleyi-EhV System. Viruses 2016, 9, 61
Viruses 2017, 9(4), 89; https://doi.org/10.3390/v9040089
Received: 11 April 2017 / Revised: 18 April 2017 / Accepted: 18 April 2017 / Published: 24 April 2017
PDF Full-text (598 KB) | HTML Full-text | XML Full-text
Abstract
The authors wish to make the following change to their paper [...] Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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