Influence of light on the infection of Aureococcus anophagefferens CCMP 1984 by a “giant virus”

The pelagophyte Aureococcus anophagefferens has caused recurrent brown tide blooms along the northeast coast of the United States since the mid-1980\u27s, and more recently spread to other regions of the globe. These blooms, due to the high cell densities, are associated with severe light attenuation that destroys the sea grass beds which provide the basis for many fisheries. Data collected by transmission electron microscopy, PCR, and metatranscriptomic studies of the blooms, support the hypothesis that large dsDNA viruses play a role in bloom dynamics. While a large (~140 nm) icosahedral virus, with a 371 kbp genome, was first isolated more than a decade ago, the constraints imposed by environmental parameters on bloom infection dynamics by Aureococcus anophagefferens Virus, (AaV) remain unknown. To investigate the role light plays in infection by this virus, we acclimated A. anophagefferens to light intensities of 30 (low), 60 (medium) or 90 μmol photons m-2 s-1 (high) and infected cultures at these irradiance levels. Moreover, we completed light shift experiments where acclimated cultures were exposed to even lower light intensities (0, 5, and 15 μmol photons m-2 s-1) consistent with irradiance found during the peak of the bloom when cell concentrations are highest. The abundance of viruses produced per lytic event (burst size) was lower in the low irradiance acclimated cultures compared to the medium and high acclimated cultures. Transferring infected cultures to more-limiting light availabilities further decreased burst size and increased the length of time it took for cultures to lyse, regardless of acclimation irradiance level. A hypothetical mechanism for the reduced efficiency of the infection cycle in low light due to ribosome biogenesis was predicted from pre-existing transcriptomes. Overall, these studies provide a framework for understanding light effects on infection dynamics over the course of the summer months when A. anophagefferens blooms occur

A Student\u27s Guide to giant Viruses Infecting Small Eukaryotes: From Acanthamoeba to Zooxanthellae

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

Influence of light on the infection of Aureococcus anophagefferens CCMP 1984 by a "giant virus".

The pelagophyte Aureococcus anophagefferens has caused recurrent brown tide blooms along the northeast coast of the United States since the mid-1980's, and more recently spread to other regions of the globe. These blooms, due to the high cell densities, are associated with severe light attenuation that destroys the sea grass beds which provide the basis for many fisheries. Data collected by transmission electron microscopy, PCR, and metatranscriptomic studies of the blooms, support the hypothesis that large dsDNA viruses play a role in bloom dynamics. While a large (~140 nm) icosahedral virus, with a 371 kbp genome, was first isolated more than a decade ago, the constraints imposed by environmental parameters on bloom infection dynamics by Aureococcus anophagefferens Virus, (AaV) remain unknown. To investigate the role light plays in infection by this virus, we acclimated A. anophagefferens to light intensities of 30 (low), 60 (medium) or 90 μmol photons m-2 s-1 (high) and infected cultures at these irradiance levels. Moreover, we completed light shift experiments where acclimated cultures were exposed to even lower light intensities (0, 5, and 15 μmol photons m-2 s-1) consistent with irradiance found during the peak of the bloom when cell concentrations are highest. The abundance of viruses produced per lytic event (burst size) was lower in the low irradiance acclimated cultures compared to the medium and high acclimated cultures. Transferring infected cultures to more-limiting light availabilities further decreased burst size and increased the length of time it took for cultures to lyse, regardless of acclimation irradiance level. A hypothetical mechanism for the reduced efficiency of the infection cycle in low light due to ribosome biogenesis was predicted from pre-existing transcriptomes. Overall, these studies provide a framework for understanding light effects on infection dynamics over the course of the summer months when A. anophagefferens blooms occur

Contrasting seasonal drivers of virus abundance and production in the North Pacific Ocean

<div><p>The North Pacific Ocean (between approximately 0°N and 50°N) contains the largest continuous ecosystem on Earth. This region plays a vital role in the cycling of globally important nutrients as well as carbon. Although the microbial communities in this region have been assessed, the dynamics of viruses (abundances and production rates) remains understudied. To address this gap, scientific cruises during the winter and summer seasons (2013) covered the North Pacific basin to determine factors that may drive virus abundances and production rates. Along with information on virus particle abundance and production, we collected a spectrum of oceanographic metrics as well as information on microbial diversity. The data suggest that both biotic and abiotic factors affect the distribution of virus particles. Factors influencing virus dynamics did not vary greatly between seasons, although the abundance of viruses was almost an order of magnitude greater in the summer. When considered in the context of microbial community structure, our observations suggest that members of the bacterial phyla Proteobacteria, Planctomycetes, and Bacteroidetes were correlated to both virus abundances and virus production rates: these phyla have been shown to be enriched in particle associated communities. The findings suggest that environmental factors influence virus community functions (<i>e</i>.<i>g</i>., virion particle degradation) and that particle-associated communities may be important drivers of virus activity.</p></div

OTU abundance and contribution to variation in viral abundance and production.

<p>Plots comparing rank order abundance for individual OTUs and contribution to the proportion of variation in virus abundance and production rates that each OTU contributes. Pairwise data are presented, rank order; contribution to virus dynamics, winter (A; B) and summer (C; D), respectively. Phyla indicated as follows: Chloroplast (i), Proteobacteria (ii), Cyanobacteria (iii), Planctomycetes (iv), Firmicutes (v), Unclassified bacteria (vi), Bacteroidetes (vii). Statistical significance indicated as follows: * = 0.001–0.01, ** = 0.01–0.05, *** = 0.05–0.1, + = > 0.1</p

Biological parameters in relationship with latitude.

<p>Cell abundances for <i>Prochlorococcus (</i>●<i>)</i>, <i>Synechococcus (</i>○<i>)</i>, <i>Picoeukaryotes (</i>▼<i>)</i>, and total bacterioplankton (including cyanobacteria) (△) across the latitudes investigated in winter (A) and summer (B). Virus abundances (●) and virus production rates (▽) for winter (C) and summer (D).</p

Relationship between temperature and virus abundances.

<p>Relationship between virus abundances and temperature for winter (●) and summer (⧠). Inset indicates average virus densities during the winter and summer cruises. * indicates a p-value <0.01.</p

Correlations between virus abundance and productions and environmental parameters.

<p>Spearman correlation coefficient shown on the x-axis and p-values indicated on the y-axis. Parameters were separated according to classifications including: physical (A), biological (B) and nutrient(c) data. Circles indicate spearman correlations of virus abundances while virus production correlations are indicated by triangles. Closed symbols = summer samples and open symbols = winter samples. Horizontal dash line (i) shows a p-value of 0.05; solid line (ii) shows a Bonferonni adjusted p-value of 0.002.</p