Discovery of a dsRNA virus infecting the marine photosynthetic protist Micromonas pusilla

AbstractWe report the isolation of the first double-stranded (ds) RNA virus in the family Reoviridae that infects a protist (microalga Micromonas pusilla, Prasinophyceae). The dsRNA genome was composed of 11 segments ranging between 0.8 and 5.8 kb, with a total size of approximately 25.5 kb. The virus (MpRNAV-01B) could not be assigned to the genus level because host type, genome size, and number of segments smaller than 2 kb did not correspond to either of the two existing 11-segmented dsRNA genera Rotavirus and Aquareovirus. MpRNAV-01B has a particle size of 65–80 nm, a narrow host range, a latent period of 36 h, and contains five major proteins (120, 95, 67, 53, and 32 kDa). MpRNAV-01B was stable to freeze–thawing, resistant to chloroform, ether, nonionic detergents, chelating and reducing agents. The virus was inactivated at temperatures above 35 °C and by ionic detergent, ethanol, acetone, and acidic conditions (pH 2–5)

Size-fractionated uptake of ammonium, nitrate and urea and phytoplankton growth in the North Sea during Spring 1994

The growth of 2 different algal size classes was studied in March/April 1994 during the establishment of the spring bloom along a transect from the Dogger Bank to the Shetland Islands in the North Sea. Size-differential growth rates were estimated on the basis of independent measurements of carbon and nitrogen uptake. At the shallower stations near the Dogger Bank (DB) area, chlorophyll a (chl a) levels were up to 5.8 mu g l(-1). In the bloom 89 % of the chi a was in the >5 mu m fraction. In the central North Sea (cNS) and near the Shetland Islands (SI) total chi a was 0.52 and 0.38 mu g l(-1), respectively; 60 % was in the >5 mu m fraction. Depth-integrated primary production at the DB, cNS and SI was 46, 145 and 149 mg C m(-2) d(-1), respectively, for the 5 mu m size fraction. Since the calculated specific growth rates, based on either nitrogen uptake or inorganic carbon uptake, were in good agreement with each other for both size fractions, it was concluded that smaller algae apparently grow faster than larger ones in this typically light-controlled environment. The >5 mu m fraction, however, dominated the bloom at the Dogger Bank. Our findings consolidate the concept of size differential control of phytoplankton communities under typical spring bloom conditions which originally was demonstrated in a coastal area (Riegman et al. 1993; Neth J Sea Res 31:255-265). [KEYWORDS: phytoplankton growth; size fractionation; nitrogen uptake; carbon uptake; North Sea Marine diatoms; cell-size; nitrogen assimilation; carbon fixation; populations; plankton; station; system; waters; light

Resistant biomacromolecules in five marine microalgae of the classes Eustigmatophyceae and Chlorophyceae: Geochemical implications

Non-hydrolysable macromolecular constituents (i.e. algaenans) were isolated from two out of seven marine microalgae investigated. Nannochloropsis salina and Nannochloropsis sp. from the class of Eustigmatophyceae produce highly aliphatic algaenans. Flash pyrolysis and chemical degradations with HI and RuO4 allowed for the identification of their chemical structure, which is mainly composed of polyether-linked long-chain (up to C36) n-alkyl units. The building blocks of this polymer were also recognized in lipid fractions. The green microalgae (Chlorophyceae) Chlorella spaerckii, Chlorococcum sp. and Nannochloris sp. were earlier thought to biosynthesize algaenans comprising aliphatic and/or aromatic moieties. However, a new isolation method utilizing trifluoroacetic acid (TFA) prior to the other hydrolyses revealed that the macromolecular material isolated from these three chlorophytes was either hydrolysable with TFA or artefacts from the former method. Similar to algaenans from fresh water green microalgae, the aliphatic eustigmatophyte algaenans are likely to be selectively preserved in depositional environments and might ultimately serve as source rock organic matter of marine crude oils. Furthermore, they may play an important role in the cycling of carbon

Novel, resistant microalgal polyethers: An important sink of organic carbon in the marine environment?

Five out of seven marine microalgal species investigated were found to biosynthesize nonhydrolysable, mainly aliphatic, biomacromolecules (algaenans). The molecular structure of the algaenan isolated from the microalga Nannochloropsis salina of the class Eustigmatophyceae was determined by solid state 13C NMR spectroscopy, Curie point pyrolysis - gas chromatography - mass spectrometry, and chemical degradations with HI and RuO4. The structure is predominantly composed of C28--C34 linear chains linked by ether bridges. The algaenan isolated from a second eustigmatophyte (Nannochloropsis sp.) was structurally similar. Algaenans isolated from two chlorophytes also possess a strongly aliphatic nature, as revealed by the dominance of alkenes/alkanes in their pyrolysates. Accordingly, we propose that the aliphatic character of numerous Recent and ancient marine kerogens reflects selectively preserved algaenans and that these algaenans may act as a source of n-alkanes in marine crude oils

Genome of <i>Phaeocystis globosa</i> virus PgV-16T highlights the common ancestry of the largest known DNA viruses infecting eukaryotes

Large dsDNA viruses are involved in the population control of many globally distributed species of eukaryotic phytoplankton and have a prominent role in bloom termination. The genus Phaeocystis (Haptophyta, Prymnesiophyceae) includes several high-biomass-forming phytoplankton species, such as Phaeocystis globosa, the blooms of which occur mostly in the coastal zone of the North Atlantic and the North Sea. Here, we report the 459,984-bp-long genome sequence of P. globosa virus strain PgV-16T, encoding 434 proteins and eight tRNAs and, thus, the largest fully sequenced genome to date among viruses infecting algae. Surprisingly, PgV-16T exhibits no phylogenetic affinity with other viruses infecting microalgae (e. g., phycodnaviruses), including those infecting Emiliania huxleyi, another ubiquitous bloom-forming haptophyte. Rather, PgV-16T belongs to an emerging clade (the Megaviridae) clustering the viruses endowed with the largest known genomes, including Megavirus, Mimivirus (both infecting acanthamoeba), and a virus infecting the marine microflagellate grazer Cafeteria roenbergensis. Seventy-five percent of the best matches of PgV-16T-predicted proteins correspond to two viruses [Organic Lake phycodnavirus (OLPV)1 and OLPV2] from a hypersaline lake in Antarctica (Organic Lake), the hosts of which are unknown. As for OLPVs and other Megaviridae, the PgV-16T sequence data revealed the presence of a virophage-like genome. However, no virophage particle was detected in infected P. globosa cultures. The presence of many genes found only in Megaviridae in its genome and the presence of an associated virophage strongly suggest that PgV-16T shares a common ancestry with the largest known dsDNA viruses, the host range of which already encompasses the earliest diverging branches of domain Eukarya

A model system approach to biological climate forcing:The example of <i>Emiliania huxleyi</i>

The following is an extended summary of the project "A model system approach to biological climate forcing: the example of Emiliania huxleyi," that was carried out within the framework of the Dutch National Programme on Air Pollution and Climate Change (NRP) - phase II. In this report the progress is described that has been made in the formulation of the Dynamic Energy Budget (DEB) Theory that now includes photosynthesis, nutrient limitation and calcification. On top of this the next level of organisation was explored in the adaptation of the model towards a small ecosystem comprising an autotrophic and a heterotrophic organism together with a decomposer, -the dynamics of biomass in vertical profiles has been analysed. At the same time experiments were conducted with E. huxleyi in order to be able to validate the DEB-models at the organismic level. The experiments involved exploration of the genes that control calcification, photosynthesis and nutrition, a detailed description of growth based on chemostat experiments, and an inventory of environmental factors that determine the production of dimethylsulfoniopropionate, the precursor of the biogenic gas dimethylsufide (DMS) that regulates climate once it has reached the atmosphere acting as a source of cloud condensation nuclei