Modeling the avoidance behavior of zooplankton on phytoplankton infected by free viruses.

In any ecosystem, chaotic situations may arise from equilibrium state for different reasons. To overcome these chaotic situations, sometimes the system itself exhibits some mechanisms of self-adaptability. In this paper, we explore an eco-epidemiological model consisting of three aquatic groups: phytoplankton, zooplankton, and marine free viruses. We assume that the phytoplankton population is infected by external free viruses and zooplankton get affected on consumption of infected phytoplankton; also, the infected phytoplankton do not compete for resources with the susceptible one. In addition, we model a mechanism by which zooplankton recognize and avoid infected phytoplankton, at least when susceptible phytoplankton are present. The zooplankton extinction chance increases on increasing the force of infection or decreasing the intensity of avoidance. Further, when the viral infection triggers chaotic dynamics, high zooplankton avoidance intensity can stabilize again the system. Interestingly, for high avoidance intensity, nutrient enrichment has a destabilizing effect on the system dynamics, which is in line with the paradox of enrichment. Global sensitivity analysis helps to identify the most significant parameters that reduce the infected phytoplankton in the system. Finally, we compare the dynamics of the system by allowing the infected phytoplankton also to share resources with the susceptible phytoplankton. A gradual increase of the virus replication factor turns the system dynamics from chaos to doubling state to limit cycle to stable state and the system finally settles down to the zooplankton-free equilibrium point. Moreover, on increasing the intensity of avoidance, the system shows a transcritical bifurcation from the zooplankton-free equilibrium to the coexistence steady state and remains stable thereafter.

Ultrastructure of Meelsvirus: A nuclear virus of arrow worms (phylum Chaetognatha) producing giant "tailed" virions.

Most known giant viruses, i.e., viruses producing giant virions, parasitize amoebae and other unicellular eukaryotes. Although they vary in the level of dependence on host nuclear functions, their virions self-assemble in the host cell's cytoplasm. Here we report the discovery of a new prototype of giant virus infecting epidermal cells of the marine arrow worm Adhesisagitta hispida. Its 1.25 µm-long virions self-assemble and accumulate in the host cell's nucleus. Conventional transmission electron microscopy reveals that the virions have a unique bipartite structure. An ovoid nucleocapsid, situated in a broad "head" end of the virion is surrounded by a thin envelope. The latter extends away from the head to form a voluminous conical "tail" filled with electron-dense extracapsidular material. The 31nm-thick capsid wall has a distinctive substructure resulting from a patterned arrangement of subunits; it bears no ultrastructural resemblance to the virion walls of other known giant viruses. The envelope self-assembles coincident with the capsid and remotely from all host membranes. We postulate that transmission to new hosts occurs by rupture of protruding virion-filled nuclei when infected arrow worms mate. Future genomic work is needed to determine the phylogenetic position of this new virus, which we have provisionally named Meelsvirus.

The End of a 60-year Riddle: Identification and Genomic Characterization of an Iridovirus, the Causative Agent of White Fat Cell Disease in Zooplankton.

The planktonic freshwater crustacean of the genus Daphnia are a model system for biomedical research and, in particular, invertebrate-parasite interactions. Up until now, no virus has been characterized for this system. Here we report the discovery of an iridovirus as the causative agent of White Fat Cell Disease (WFCD) in Daphnia WFCD is a highly virulent disease of Daphnia that can easily be cultured under laboratory conditions. Although it has been studied from sites across Eurasia for more than 60 years, its causative agent had not been described, nor had an iridovirus been connected to WFCD before now. Here we find that an iridovirus-the Daphnia iridescent virus 1 (DIV-1)-is the causative agent of WFCD. DIV-1 has a genome sequence of about 288 kbp, with 39% G+C content and encodes 367 predicted open reading frames. DIV-1 clusters together with other invertebrate iridoviruses but has by far the largest genome among all sequenced iridoviruses. Comparative genomics reveal that DIV-1 has apparently recently lost a substantial number of unique genes but has also gained genes by horizontal gene transfer from its crustacean host. DIV-1 represents the first invertebrate iridovirus that encodes proteins to purportedly cap RNA, and it contains unique genes for a DnaJ-like protein, a membrane glycoprotein and protein of the immunoglobulin superfamily, which may mediate host-pathogen interactions and pathogenicity. Our findings end a 60-year search for the causative agent of WFCD and add to our knowledge of iridovirus genomics and invertebrate-virus interactions.

Species composition of testate amoebae in Lake Monte Alegre, Ribeirão Preto, SP, Brazil / Composição de amebas testáceas no lago Monte Alegre, Ribeirão Preto, SP, Brasil

We aimed to perform the first survey of testate amoebae community composition in Lake Monte Alegre at São Paulo state, and contribute to mitigate the taxonomic impediment regarding thediversity of testate amoebae in Brazil. Samplings were performed in 20 sampling sites within the lake, inthe limnetic and littoral regions in April 2015, using a 58 μm-meshplankton net. We identified 20 taxa oftestate amoebae belonging to four families: Arcellidae (8 taxa), Centropyxidae (4 taxa), Difflugiidae (7 taxa) and Lesquereusiidae (2 taxa). The littoral region showed the highest number of taxa (n = 20), whereas inthe limnetic region 11 taxa were registered. Therefore, our results evidenced the importance of testateamoebae in aquatic systems, and that further research, taxonomic and/or ecological, in those environmentsshould include these organisms in their investigation. Moreover, we suggest that future research with greater sampling effort is necessary to expand the identification of possible cryptic species in this environment.

O objetivo deste estudo foi realizar o primeiro levantamento da composição da comunidade de amebas testáceas no lago Monte Alegre no Estado de São Paulo e, assim, contribuir para mitigar oimpedimento taxonômico relacionado à diversidade de amebas testáceas no Brasil. As amostragens foramrealizadas em 20 pontos do lago, nas regiões limnética e litorânea, no mês de abril de 2015, com rede deplâncton de 58 μm de abertura de malha. Foram identificados 20 táxons de amebas testáceas, divididos emquatro famílias: Arcellidae (8 táxons), Centropyxidae (4 táxons), Difflugiidae (7 táxons) e Lesquereusiidae(2 táxons). A região litorânea apresentou o maior número de táxons (n = 20), enquanto que na regiãolimnética foram registrados 11 táxons. Diante disso, é possível indicar que os nossos resultados evidenciama importância das amebas testáceas nos sistemas aquáticos e que novos estudos, taxonômicos e/ou ecológicos, nesses ambientes devem incluir estes organismos em suas investigações. Além disso, sugeremsefuturos estudos com maior esforço amostral para ampliar a identificação de possíveis espécies crípticas noambiente.

Statistical Mechanics of Zooplankton.

Statistical mechanics provides the link between microscopic properties of many-particle systems and macroscopic properties such as pressure and temperature. Observations of similar "microscopic" quantities exist for the motion of zooplankton, as well as many species of other social animals. Herein, we propose to take average squared velocities as the definition of the "ecological temperature" of a population under different conditions on nutrients, light, oxygen and others. We test the usefulness of this definition on observations of the crustacean zooplankton Daphnia pulicaria. In one set of experiments, D. pulicaria is infested with the pathogen Vibrio cholerae, the causative agent of cholera. We find that infested D. pulicaria under light exposure have a significantly greater ecological temperature, which puts them at a greater risk of detection by visual predators. In a second set of experiments, we observe D. pulicaria in cold and warm water, and in darkness and under light exposure. Overall, our ecological temperature is a good discriminator of the crustacean's swimming behavior.

Zooplankton may serve as transmission vectors for viruses infecting algal blooms in the ocean.

Marine viruses are recognized as a major driving force regulating phytoplankton community composition and nutrient cycling in the oceans. Yet, little is known about mechanisms that influence viral dispersal in aquatic systems, other than physical processes, and that lead to the rapid demise of large-scale algal blooms in the oceans. Here, we show that copepods, abundant migrating crustaceans that graze on phytoplankton, as well as other zooplankton can accumulate and mediate the transmission of viruses infecting Emiliania huxleyi, a bloom-forming coccolithophore that plays an important role in the carbon cycle. We detected by PCR that >80% of copepods collected during a North Atlantic E. huxleyi bloom carried E. huxleyi virus (EhV) DNA. We demonstrated by isolating a new infectious EhV strain from a copepod microbiome that these viruses are infectious. We further showed that EhVs can accumulate in high titers within zooplankton guts during feeding or can be adsorbed to their surface. Subsequently, EhV can be dispersed by detachment or via viral-dense fecal pellets over a period of 1 day postfeeding on EhV-infected algal cells, readily infecting new host populations. Intriguingly, the passage through zooplankton guts prolonged EhV's half-life of infectivity by 35%, relative to free virions in seawater, potentially enhancing viral transmission. We propose that zooplankton, swimming through topographically adjacent phytoplankton micropatches and migrating daily over large areas across physically separated water masses, can serve as viral vectors, boosting host-virus contact rates and potentially accelerating the demise of large-scale phytoplankton blooms.

Molecular and microscopic evidence of viruses in marine copepods.

As dominant members of marine mesozooplankton communities, copepods play critical roles in oceanic food webs and biogeochemical cycling. Despite the ecological significance of copepods, little is known regarding the causes of copepod mortality, and up to 35% of total copepod mortality cannot be accounted for by predation alone. Viruses have been established as ecologically important infectious agents in the oceans; however, viral infection has not been investigated in mesozooplankton communities. Here we used molecular and microscopic techniques to document viral infection in natural populations of the calanoid copepods Acartia tonsa (Dana) and Labidocera aestiva (Wheeler) in Tampa Bay, FL. Viral metagenomics revealed previously undocumented viruses in each species, named Acartia tonsa copepod circo-like virus (AtCopCV) and Labidocera aestiva copepod circo-like virus (LaCopCV). LaCopCV was found to be extremely prevalent and abundant in L. aestiva populations, with up to 100% prevalence in some samples and average viral loads of 1.13 × 10(5) copies per individual. LaCopCV transcription was also detected in the majority of L. aestiva individuals, indicating viral activity. AtCopCV was sporadically detected in A. tonsa populations year-round, suggesting temporal variability in viral infection dynamics. Finally, virus-like particles of unknown identity were observed in the connective tissues of A. tonsa and L. aestiva by transmission electron microscopy, demonstrating that viruses were actively proliferating in copepod connective tissue as opposed to infecting gut contents, parasites, or symbionts. Taken together, these results provide strong independent lines of evidence for active viral infection in dominant copepod species, indicating that viruses may significantly influence mesozooplankton ecology.

Another really, really big virus.

Viruses with genomes larger than 300 kb and up to 1.2 Mb, which encode hundreds of proteins, are being discovered and characterized with increasing frequency. Most, but not all, of these large viruses (often referred to as giruses) infect protists that live in aqueous environments. Bioinformatic analyses of metagenomes of aqueous samples indicate that large DNA viruses are quite common in nature and await discovery. One issue that is perhaps not appreciated by the virology community is that large viruses, even those classified in the same family, can differ significantly in morphology, lifestyle, and gene complement. This brief commentary, which will mention some of these unique properties, was stimulated by the characterization of the newest member of this club, virus CroV (Fischer, M.G.; Allen, M.J.; Wilson, W.H.; Suttle, C.A. Giant virus with a remarkable complement of genes infects marine zooplankton. Proc. Natl. Acad. Sci. USA 2010, 107, 19508-19513). CroV has a 730 kb genome (with ∼544 protein-encoding genes) and infects the marine microzooplankton Cafeteria roenbergensis producing a lytic infection.

Detection of cyprinid herpesvirus-3 DNA in lake plankton.

The disease caused by cyprinid herpesvirus-3 (CyHV-3) severely impacts the natural freshwater ecosystem and damages carp and koi farming, however, the pathway of CyHV-3 transmission remains unclear. It is possible that the virus adheres to plankton, which then facilitate viral movement and transmission, and therefore, it is hypothesised that plankton are involved in the disease dynamics. In this study, plankton were collected at eight sites in the Iba-naiko lagoon; we detected and quantified CyHV-3 DNA from plankton samples. The results of the correlation analysis showed a significant positive correlation between CyHV-3 copies and the number of Rotifera, suggesting that CyHV-3 binds to and/or is concentrated by Rotifera. Our results suggest that plankton affect viral ecology in the natural environment.

Giant virus with a remarkable complement of genes infects marine zooplankton.

As major consumers of heterotrophic bacteria and phytoplankton, microzooplankton are a critical link in aquatic foodwebs. Here, we show that a major marine microflagellate grazer is infected by a giant virus, Cafeteria roenbergensis virus (CroV), which has the largest genome of any described marine virus (≈730 kb of double-stranded DNA). The central 618-kb coding part of this AT-rich genome contains 544 predicted protein-coding genes; putative early and late promoter motifs have been detected and assigned to 191 and 72 of them, respectively, and at least 274 genes were expressed during infection. The diverse coding potential of CroV includes predicted translation factors, DNA repair enzymes such as DNA mismatch repair protein MutS and two photolyases, multiple ubiquitin pathway components, four intein elements, and 22 tRNAs. Many genes including isoleucyl-tRNA synthetase, eIF-2γ, and an Elp3-like histone acetyltransferase are usually not found in viruses. We also discovered a 38-kb genomic region of putative bacterial origin, which encodes several predicted carbohydrate metabolizing enzymes, including an entire pathway for the biosynthesis of 3-deoxy-d-manno-octulosonate, a key component of the outer membrane in Gram-negative bacteria. Phylogenetic analysis indicates that CroV is a nucleocytoplasmic large DNA virus, with Acanthamoeba polyphaga mimivirus as its closest relative, although less than one-third of the genes of CroV have homologs in Mimivirus. CroV is a highly complex marine virus and the only virus studied in genetic detail that infects one of the major groups of predators in the oceans.

Norovirus distribution within an estuarine environment.

Human norovirus (NoV) has been studied extensively as an important cause of gastroenteritis outbreaks worldwide. While oysters are a primary vehicle for infection, few studies have examined the wider distribution of NoV in the estuarine environment. Active shellfish-harvesting areas in Georgia were examined for the prevalence, genotype diversity, and concentrations of NoV in a variety of estuarine sample types over the course of 1 year. Of the 225 samples (9 oyster, 72 water, 72 63- to 200-microm plankton, and 72 >200-microm plankton) collected from 12 stations across two estuaries, 21 samples (9.3%) tested positive for NoV. By sample type, 55.0% (5/9) of oysters, 8.3% (6/72) of water samples, 11.1% (8/72) of 63- to 200-microm plankton samples, and 2.8% (2/72) of >200-microm plankton samples were positive for human NoV. The two NoV-positive >200-microm plankton samples, which contained mainly zooplankton, had the greatest quantity of NoV genomes (3.5 x 10(13) and 1.7 x 10(15) genomes g(-1)) of any sample tested. The majority, 90.5% (19/21), of the samples tested positive for genogroup I NoV, and only 9.5% (2/21) of the samples tested positive for genogroup II. The high concentrations of NoV in plankton samples compared to water and oyster samples were unexpected and provide new insights into the presence and distribution of human NoV in the water environment.

The role of virus infection in a simple phytoplankton zooplankton system.

Many planktonic species show spectacular bursts ("blooms") in population density. Though viral infections are known to cause behavioural and other changes in phytoplankton and other aquatic species, yet their role in regulating the phytoplankton population is still far from being understood. To study the role of viral diseases in the planktonic species, we model the phytoplankton-zooplankton system as a prey-predator system. Here the prey (phytoplankton) species is infected with a viral disease that divides the prey population into susceptible and infected classes, with the infected prey being more vulnerable to predation by the predator (zooplankton). The dynamical behaviour of the system is investigated from the point of view of stability and persistence both analytically and numerically. The model shows that infection can be sustained only above a threshold of force of infection, and, there exists a range in the infection rate where this system shows "bloom"-like stable limit cycle oscillations. The time series of natural "blooms" with different types of irregular oscillations can arise in this model simply from a biologically realistic feature, i.e., by the random variation of the epidemiological parameter (rate of infection) in the infected prey population. The difference in mean strength of infection alone can lead to the different types of patterns observed in natural planktonic blooms.

Detection of marine birnavirus genome in zooplankton collected from the Uwa Sea, Japan.

Marine birnaviruses (MABVs) infect a wide range of fish and shellfish, yet their mode of transmission is still unclear. To determine whether marine plankton serve as a vector for MABVs, we examined plankton collected from the Uwa Sea, Japan. The phytoplankton and zooplankton were collected monthly, at depths of 0 and 40 m, from May to November 2001. Detection of the MABV genome was carried out using 2-step PCR and virus isolation. Viral genome was detected in zooplankton collected at 0 m depth in September and at 40 m depth in November. The virus could not be isolated in the PCR-positive samples. These results suggest that zooplankton may act as a vector of MABVs, although the infective and/or accumulated virus titer in zooplankton was low.