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Ocean acidification (OA), a consequence of anthropogenic carbon dioxide (CO 2 ) emissions, strongly impacts marine ecosystems. OA also influences iron (Fe) solubility, affecting biogeochemical and ecological processes. We investigated the interactive effects of CO 2 and Fe availability on the metabolome response of a natural phytoplankton community. Using mesocosms we exposed phytoplankton to ambient (390 μatm) or future CO 2 levels predicted for the year 2100 (900 μatm), combined with ambient (4.5 nM) or high (12 nM) dissolved iron (dFe). By integrating over the whole phytoplankton community, we assigned functional changes based on altered metabolite concentrations. Our study revealed the complexity of phytoplankton metabolism. Metabolic profiles showed three stages in response to treatments and phytoplankton dynamics. Metabolome changes were related to the plankton group contributing respective metabolites, explaining bloom decline and community succession. CO 2 and Fe affected metabolic profiles. Most saccharides, fatty acids, amino acids and many sterols significantly correlated with the high dFe treatment at ambient pCO 2 . High CO 2 lowered the abundance of many metabolites irrespective of Fe. However, sugar alcohols accumulated, indicating potential stress. We demonstrate that not only altered species composition but also changes in the metabolic landscape affecting the plankton community may change as a consequence of future high-CO 2 oceans., (© 2020 Society for Applied Microbiology and John Wiley & Sons Ltd.)

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.

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.

Microalgae in the division Haptophyta play key roles in the marine ecosystem and in global biogeochemical processes. Despite their ecological importance, knowledge on seasonal dynamics, community composition and abundance at the species level is limited due to their small cell size and few morphological features visible under the light microscope. Here, we present unique data on haptophyte seasonal diversity and dynamics from two annual cycles, with the taxonomic resolution and sampling depth obtained with high-throughput sequencing. From outer Oslofjorden, S Norway, nano- and picoplanktonic samples were collected monthly for 2 years, and the haptophytes targeted by amplification of RNA/cDNA with Haptophyta-specific 18S rDNA V4 primers. We obtained 156 operational taxonomic units (OTUs), from c. 400.000 454 pyrosequencing reads, after rigorous bioinformatic filtering and clustering at 99.5%. Most OTUs represented uncultured and/or not yet 18S rDNA-sequenced species. Haptophyte OTU richness and community composition exhibited high temporal variation and significant yearly periodicity. Richness was highest in September-October (autumn) and lowest in April-May (spring). Some taxa were detected all year, such as Chrysochromulina simplex, Emiliania huxleyi and Phaeocystis cordata, whereas most calcifying coccolithophores only appeared from summer to early winter. We also revealed the seasonal dynamics of OTUs representing putative novel classes (clades HAP-3-5) or orders (clades D, E, F). Season, light and temperature accounted for 29% of the variation in OTU composition. Residual variation may be related to biotic factors, such as competition and viral infection. This study provides new, in-depth knowledge on seasonal diversity and dynamics of haptophytes in North Atlantic coastal waters., (© 2015 The Authors. Molecular Ecology Published by John Wiley & Sons Ltd.)

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., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Marine viruses are major evolutionary and biogeochemical drivers in marine microbial foodwebs. However, an in-depth understanding of the cellular mechanisms and the signal transduction pathways mediating host-virus interactions during natural bloom dynamics has remained elusive. We used field-based mesocosms to examine the "arms race" between natural populations of the coccolithophore Emiliania huxleyi and its double-stranded DNA-containing coccolithoviruses (EhVs). Specifically, we examined the dynamics of EhV infection and its regulation of cell fate over the course of bloom development and demise using a diverse suite of molecular tools and in situ fluorescent staining to target different levels of subcellular resolution. We demonstrate the concomitant induction of reactive oxygen species, caspase-specific activity, metacaspase expression, and programmed cell death in response to the accumulation of virus-derived glycosphingolipids upon infection of natural E. huxleyi populations. These subcellular responses to viral infection simultaneously resulted in the enhanced production of transparent exopolymer particles, which can facilitate aggregation and stimulate carbon flux. Our results not only corroborate the critical role for glycosphingolipids and programmed cell death in regulating E. huxleyi-EhV interactions, but also elucidate promising molecular biomarkers and lipid-based proxies for phytoplankton host-virus interactions in natural systems.

The isolation and characterization of a virus (designated EhV) that infects the marine coccolithophorid Emiliania huxleyi (Lohmann) Hay & Mohler are described. Three independent clones of EhV were isolated from Norwegian coastal waters in years 1999 and 2000. EhV is a double-stranded DNA-containing virus with a genome size of ∼415 kilo-base pairs. The viral particle is an icosahedron with a diameter of 160–180 nm. The virus particle contains at least nine proteins ranging from 10 to 140 kDa; the major capsid protein weighs ∼54 kDa. EhV has a latent period of 12–14 h and a burst size of 400–1000 (mean, 620) viral particles per cell. A phylogenetic tree based on DNA polymerase amino acid sequences indicates EhV should be assigned to the Phycodnaviridae virus family and that the virus is most closely related to viruses that infect Micromonas pusilla and certain Chlorella species. [ABSTRACT FROM AUTHOR]

The isolation and characterization of a virus (designated EhV) that infects the marine coccolithophorid Emiliania huxleyi (Lohmann) Hay & Mohler are described. Three independent clones of EhV were isolated from Norwegian coastal waters in years 1999 and 2000. EhV is a double-stranded DNA-containing virus with a genome size of ∼415 kilo-base pairs. The viral particle is an icosahedron with a diameter of 160–180 nm. The virus particle contains at least nine proteins ranging from 10 to 140 kDa; the major capsid protein weighs ∼54 kDa. EhV has a latent period of 12–14 h and a burst size of 400–1000 (mean, 620) viral particles per cell. A phylogenetic tree based on DNA polymerase amino acid sequences indicates EhV should be assigned to the Phycodnaviridae virus family and that the virus is most closely related to viruses that infect Micromonas pusilla and certain Chlorella species. [ABSTRACT FROM AUTHOR]