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Corina P D Brussaard - One of the best experts on this subject based on the ideXlab platform.

  • virus production in phosphorus limited Micromonas pusilla stimulated by a supply of naturally low concentrations of different phosphorus sources far into the lytic cycle
    FEMS Microbiology Ecology, 2016
    Co-Authors: D. S. Maat, Harry J Witte, Judith Van Bleijswijk, Corina P D Brussaard
    Abstract:

    Earlier studies show that the proliferation of phytoplankton viruses can be inhibited by depletion of soluble reactive phosphorus (SRP; orthophosphate). In natural marine waters, phytoplankton phosphorus (P) availability is, however, largely determined by the supply rate of SRP (e.g. through remineralization) and potentially by the source of P as well (i.e. the utilization of soluble non-reactive P; SNP). Here we show how a steady low supply of P (mimicking natural P recycling) to virally infected P-limited Micromonas pusilla stimulates virus proliferation. Independent of the degree of P limitation prior to infection (0.32 and 0.97μmax chemostat cultures), SRP supply resulted in 2-fold higher viral burst sizes (viruses lysed per host cell) as compared with no addition (P starvation). Delaying these spikes during the infection cycle showed that the added SRP was utilized for extra M. pusilla virus (MpV) production far into the lytic cycle (18 h post-infection). Moreover, P-limited M. pusilla utilized several SNP compounds with high efficiency and with the same extent of burst size stimulation as for SRP. Finally, addition of virus-free MpV lysate (representing a complex SNP mixture) to newly infected cells enhanced MpV production, implicating host-associated alkaline phosphatase activity, and highlighting its important role in oligotrophic environments

  • combined phosphorus limitation and light stress prevent viral proliferation in the phytoplankton species phaeocystis globosa but not in Micromonas pusilla
    Frontiers in Marine Science, 2016
    Co-Authors: D. S. Maat, Reinhoud De Blok, Corina P D Brussaard
    Abstract:

    Under natural conditions phytoplankton are often simultaneously subjected to phosphorus (P) limitation and suboptimal light levels. Potential interacting effects of P-limitation and light availability on phytoplankton virus-host interactions have thus far not been reported. We studied the influence of three environmentally relevant light levels (low; 25, medium; 100 and high; 250 µmol quanta m-2 s-1) in combination with P-limitation (vs. P-replete conditions) on virus proliferation in the key phytoplankton species Micromonas pusilla and Phaeocystis globosa. Cultures were acclimated to balanced P-limited growth at 3 light levels by semi-continuous culturing, before one-step infection experiments were carried out in batch mode. Under optimal conditions (medium light, P-replete), the latent period (time until first release of progeny viruses) was 6-9 h and 9-12 h, and the burst size (number of viruses released per lysed host cell) was 241±5 and 690±28 for M. pusilla virus MpV and P. globosa virus PgV, respectively. Low light intensity under P-replete conditions prolonged the latent period of PgV (with maximally 3 h). The PgV burst size was 2.8-fold reduced under low light and 2.2-fold reduced under high light. The 10-fold range in light intensity did not affect viral latent period or burst size in P-replete M. pusilla. However, P-limitation (under optimal light) also led to elongated latent periods (with maximally 3 h compared to P-replete) and the viral burst sizes decreased by 2.7-fold for MpV and 3.5-fold for PgV. Finally, infectivity assays showed that PgV progeny from the P-limited high and low light cultures largely lost their infectivity, reducing their infective burst sizes to only 2-4 infective viruses per lysed host cell. Our study demonstrates that the effects of specific light and P-availability on virus-phytoplankton interaction are not only species specific, but can also strengthen each other’s effects. Relatively small differences in environmental conditions with depth, geography or time have the potential to drastically affect viral infection of phytoplankton, with consequent effects on host species composition and biogeochemical fluxes.

  • Both phosphorus- and nitrogen limitation constrain viral proliferation in marine phytoplankton
    Aquatic Microbial Ecology, 2016
    Co-Authors: D. S. Maat, Corina P D Brussaard
    Abstract:

    Through cell lysis, viruses shape phytoplankton community composition and stimulate biogeochemical cycling in the oceans. Earlier studies indicate that reduced phosphorus (P) availability can affect phytoplankton virus proliferation. The effects of nitrogen (N) availability are claimed to be weaker than those for P, but this has not been thoroughly studied. Here, we investigated how N-limiting growth conditions, resulting in altered algal elemental stoichiometry and physiology, affected virus proliferation in the phytoplankters Micromonas pusilla and Phaeocystis globosa. Algal cultures were adapted to balanced nutrient-limited growth, i.e. N-, P- and NP-controlled growth, before infection with their respective viruses MpV-08T and PgV-07T. The viral infection experiments were then performed in batch cultures to allow optimal 1-step virus growth cycles. Compared to the nutrient-replete cultures, infection of nutrient-controlled hosts resulted in elongated latent periods (time until first virus release) and reduced viral burst sizes (viruses lysed host cell-1) for both MpV and PgV. For MpV, the viral burst size was reduced by 70%, independent of the type of nutrient. The burst size of PgV was most reduced under N-limitation, by as much as 92%, compared to 70% under P-limitation. Overall, our results demonstrate that algal virus production can be strongly impaired by N-limitation and that the effects are of a similar magnitude to or even larger than for P. Our study indicates that viral control of natural phytoplankton populations might be strongly driven by both P- and N-availability.

  • Increasing P-stress and viral infection impact lipid remodeling of the picophytoplankter Micromonas pusilla
    Biogeosciences Discussions, 2015
    Co-Authors: D. S. Maat, N. J. Bale, E. C. Hopmans, J. S. Sinninghe Damsté, S. Schouten, Corina P D Brussaard
    Abstract:

    Abstract. The intact polar lipid (IPL) composition of phytoplankton is plastic and dependent on environmental factors. Previous studies have shown that phytoplankton under phosphorus (P)-stress substitute phosphatidylglycerols (PGs) with sulphoquinovosyldiacylglycerols (SQDGs) and digalactosyldiacylglycerols (DGDGs). However, these studies focused merely on P-depletion, while phytoplankton in the natural environment often experience P-limitation whereby the degree of limitation depends on the supply rate of the limiting nutrient. Here we demonstrate a linear increase in SQDG : PG and DGDG : PG ratios with increasing cellular P-stress in the picophotoeukaryote Micromonas pusilla, obtained by P-replete, P-limited (chemostat) and P-starved (no supply of P) culturing conditions. These ratios were not affected by the degree of the P-limiting conditions itself (i.e. 0.97 and 0.32 μmax chemostats), suggesting there is a minimum requirement of PGs for the maintenance of cell growth. Viral infection reduced the increase in SQDG : PG and DGDG : PG ratios in P-starved cells, but the extent did depend on the growth rate of the cultures before infection. The membrane of M. pusilla virus MpV itself was lacking some IPLs compared to the host as, e.g. no monogalactosyldiacylglycerols could be detected. Growth of the phytoplankton cultures under enhanced CO2 concentration did not affect the lipid remodeling results. The present study provides new insights into how the P-related trophic state of an ecosystem as well as viral infection can affect phytoplankton IPL composition, and therefore influence food web dynamics and biogeochemical cycling.

  • increasing p limitation and viral infection impact lipid remodeling of the picophytoplankter Micromonas pusilla
    Biogeosciences, 2015
    Co-Authors: D. S. Maat, N. J. Bale, E. C. Hopmans, S. Schouten, J Sinninghe S Damste, Corina P D Brussaard
    Abstract:

    Abstract. The intact polar lipid (IPL) composition of phytoplankton is plastic and dependent on environmental factors. Previous studies have shown that phytoplankton under low phosphorus (P) availability substitutes phosphatidylglycerols (PGs) with sulfoquinovosyldiacylglycerols (SQDGs) and digalactosyldiacylglycerols (DGDGs). However, these studies focused merely on P depletion, while phytoplankton in the natural environment often experience P limitation whereby the strength depends on the supply rate of the limiting nutrient. Here we report on the IPL composition of axenic cultures of the picophotoeukaryote Micromonas pusilla under different degrees of P limitation, i.e., P-controlled chemostats at 97 and 32 % of the maximum growth rate, and P starvation (obtained by stopping P supply to these chemostats). P-controlled cultures were also grown at elevated partial carbon dioxide pressure (pCO2) to mimic a future scenario of strengthened vertical stratification in combination with ocean acidification. Additionally, we tested the influence of viral infection for this readily infected phytoplankton host species. Results show that both SQDG : PG and DGDG : PG ratios increased with enhanced P limitation. Lipid composition was, however, not affected by enhanced (750 vs. 370 µatm) pCO2. In the P-starved virally infected cells the increase in SQDG : PG and DGDG : PG ratios was lower, whereby the extent depended on the growth rate of the host cultures before infection. The lipid membrane of the virus MpV-08T itself lacked some IPLs (e.g., monogalactosyldiacylglycerols; MGDGs) in comparison with its host. This study demonstrates that, besides P concentration, also the P supply rate, viral infection and even the history of the P supply rate can affect phytoplankton lipid composition (i.e., the non-phospholipid : phospholipid ratio), with possible consequences for the nutritional quality of phytoplankton.

Curtis A Suttle - One of the best experts on this subject based on the ideXlab platform.

  • Transcriptional responses of the marine green alga Micromonas pusilla and an infecting prasinovirus under different phosphate conditions
    Environmental Microbiology, 2018
    Co-Authors: Charles Bachy, Curtis A Suttle, Christina J. Charlesworth, Amy M. Chan, Jan F. Finke, Chee-hong Wong, Sebastian Sudek, Maureen L. Coleman, Alexandra Z. Worden
    Abstract:

    Prasinophytes are widespread marine algae for which responses to nutrient limitation and viral infection are not well understood. We studied the picoprasinophyte, Micromonas pusilla, grown under phosphate‐replete (0.65 ± 0.07 d⁻¹) and 10‐fold lower (low)‐phosphate (0.11 ± 0.04 d⁻¹) conditions, and infected by the phycodnavirus MpV‐SP1. Expression of 17% of Micromonas genes in uninfected cells differed by >1.5‐fold (q 

  • transcriptional responses of the marine green alga Micromonas pusilla and an infecting prasinovirus under different phosphate conditions
    Environmental Microbiology, 2018
    Co-Authors: Charles Bachy, Curtis A Suttle, Christina J. Charlesworth, Amy M. Chan, Jan F. Finke, Chee-hong Wong, Sebastian Sudek, Maureen L. Coleman, Alexandra Z. Worden
    Abstract:

    : Prasinophytes are widespread marine algae for which responses to nutrient limitation and viral infection are not well understood. We studied the picoprasinophyte, Micromonas pusilla, grown under phosphate-replete (0.65 ± 0.07 d-1 ) and 10-fold lower (low)-phosphate (0.11 ± 0.04 d-1 ) conditions, and infected by the phycodnavirus MpV-SP1. Expression of 17% of Micromonas genes in uninfected cells differed by >1.5-fold (q < 0.01) between nutrient conditions, with genes for P-metabolism and the uniquely-enriched Sel1-like repeat (SLR) family having higher relative transcript abundances, while phospholipid-synthesis genes were lower in low-P than P-replete. Approximately 70% (P-replete) and 30% (low-P) of cells were lysed 24 h post-infection, and expression of ≤5.8% of host genes changed relative to uninfected treatments. Host genes for CAZymes and glycolysis were activated by infection, supporting importance in viral production, which was significantly lower in slower growing (low-P) hosts. All MpV-SP1 genes were expressed, and our analyses suggest responses to differing host-phosphate backgrounds involve few viral genes, while the temporal program of infection involves many more, and is largely independent of host-phosphate background. Our study (i) identifies genes previously unassociated with nutrient acclimation or viral infection, (ii) provides insights into the temporal program of prasinovirus gene expression by hosts and (iii) establishes cell biological aspects of an ecologically important host-prasinovirus system that differ from other marine algal-virus systems.

  • variation in the genetic repertoire of viruses infecting Micromonas pusilla reflects horizontal gene transfer and links to their environmental distribution
    Viruses, 2017
    Co-Authors: Jan F. Finke, Amy M. Chan, Danielle M Winget, Curtis A Suttle
    Abstract:

    Prasinophytes, a group of eukaryotic phytoplankton, has a global distribution and is infected by large double-stranded DNA viruses (prasinoviruses) in the family Phycodnaviridae. This study examines the genetic repertoire, phylogeny, and environmental distribution of phycodnaviruses infecting Micromonas pusilla, other prasinophytes and chlorophytes. Based on comparisons among the genomes of viruses infecting M. pusilla and other phycodnaviruses, as well as the genome from a host isolate of M. pusilla, viruses infecting M. pusilla (MpVs) share a limited set of core genes, but vary strongly in their flexible pan-genome that includes numerous metabolic genes, such as those associated with amino acid synthesis and sugar manipulation. Surprisingly, few of these presumably host-derived genes are shared with M. pusilla, but rather have their closest non-viral homologue in bacteria and other eukaryotes, indicating horizontal gene transfer. A comparative analysis of full-length DNA polymerase (DNApol) genes from prasinoviruses with their overall gene content, demonstrated that the phylogeny of DNApol gene fragments reflects the gene content of the viruses; hence, environmental DNApol gene sequences from prasinoviruses can be used to infer their overall genetic repertoire. Thus, the distribution of virus ecotypes across environmental samples based on DNApol sequences implies substantial underlying differences in gene content that reflect local environmental conditions. Moreover, the high diversity observed in the genetic repertoire of prasinoviruses has been driven by horizontal gene transfer throughout their evolutionary history, resulting in a broad suite of functional capabilities and a high diversity of prasinovirus ecotypes.

  • The use of degenerate-primed random amplification of polymorphic DNA (DP-RAPD) for strain-typing and inferring the genetic similarity among closely related viruses.
    Journal of Virological Methods, 2004
    Co-Authors: André M. Comeau, Steven M. Short, Curtis A Suttle
    Abstract:

    Often it is necessary to distinguish among strains of closely related viruses, as well as infer the genetic relatedness within large groups of viruses. Current methods for strain-typing viruses are time-consuming, require significant quantities of extracted DNA, and/or may require a priori genetic information. In this study we modified random amplification of polymorphic DNA (RAPD) by using a degenerate primer to produce unique and reproducible banding patterns from viral genomes. In the degenerate-primed RAPD analysis (DP-RAPD), a selection of algal virus and bacteriophage strains were profiled that encompassed an array of genome sizes and virus families. Closely related viruses (e.g. strains infecting Micromonas pusilla) generated similar, yet unique DP-RAPD patterns that could be readily distinguished from viruses within the same family (Phycodnaviridae) infecting a Chlorella-like alga. As well, marine vibriophage from the families Myoviridae, Siphoviridae, and Podoviridae showed high diversity and were distinct from coliphage and cyanophage. Contamination of host DNA, even at levels above those that would normally be encountered, did not interfere with the viral patterns. These findings describe a rapid, PCR-based tool for strain-typing viral isolates that allows inferences to be made on genetic relatedness within groups of closely related viruses.

  • Genetic Diversity in Marine Algal Virus Communities as Revealed by Sequence Analysis of DNA Polymerase Genes
    Applied and Environmental Microbiology, 1996
    Co-Authors: Feng Chen, Curtis A Suttle, Steven M. Short
    Abstract:

    Algal-virus-specific PCR primers were used to amplify DNA polymerase gene (pol) fragments (683 to 689 bp) from the virus-sized fraction (0.02 to 0.2 microns) concentrated from inshore and offshore water samples collected from the Gulf of Mexico. Algal-virus-like DNA pol genes were detected in five samples collected from the surface and deep chlorophyll maximum. PCR products from an offshore station were cloned, and the genetic diversity of 33 fragments was examined by restriction fragment length polymorphism and sequence analysis. The five different genotypes or operational taxonomic units (OTUs) that were identified on the basis of restriction fragment length polymorphism banding patterns were present in different relative abundances (9 to 34%). One clone from each OTU was sequenced, and phylogenetic analysis showed that all of the OTUs fell within the family Phycodnaviridae. Four of the OTUs fell within a group of viruses (MpV) which infect the photosynthetic picoplankter Micromonas pusilla. The genetic diversity among these genotypes was as large as that previously found for MpV isolates from different oceans. The remaining genotype formed its own clade between viruses which infect M. pusilla and Chrysochromulina brevifilum. These results imply that marine virus communities contain a diverse assemblage of MpV-like viruses, as well as other unknown members of the Phycodnaviridae.

Gunnar Bratbak - One of the best experts on this subject based on the ideXlab platform.

  • discovery of a dsrna virus infecting the marine photosynthetic protist Micromonas pusilla
    Virology, 2004
    Co-Authors: Corina P D Brussaard, Mikal Heldal, Ruthanne Sandaa, A A M Noordeloos, Gunnar Bratbak
    Abstract:

    Abstract We 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).

  • Effects of ultraviolet radiation on marine virus–phytoplankton interactions
    FEMS Microbiology Ecology, 2003
    Co-Authors: Stéphan Jacquet, Gunnar Bratbak
    Abstract:

    Ambient ultraviolet radiation (UVR) is harmful to many biological systems and increased UVR, due to a reduced ozone layer, may have many unforeseen consequences. Viruses are the most abundant biological particles in the sea and are thought to play an important role in the structure and functioning of aquatic ecosystems. Although an increasing number of studies have been published during the last 15 years, aquatic viral ecology is still in its infancy and little is known about the effect of environmental factors on virus life cycle and host–virus interactions. Using flow cytometry, we have investigated the effect of UVR (UVB intensity: 0.22 W m−2 and UVA/UVB ratio ∼30) on five different cultured marine phytoplankton host–virus systems (CeV-Chrysochromulina ericina, EhV-Emiliania huxleyi, MpV-Micromonas pusilla, PpV-Phaeocystis pouchetii and PoV-Pyramimonas orientalis). Viruses appear to be susceptible to UV, but also they might provide some protection to their hosts. It is shown that (i) some of the investigated microalgae that have been co-cultured with viruses are less sensitive (e.g. P. pouchetii, M. pusilla) to UVB stress compared to susceptible microalgae (i.e. virus-free cultures), (ii) different viruses have different sensitivities to UVB in terms of both their abundance patterns (no effect for most of them except EhV) and infectivity (from no effect for PoV, to complete inactivation for PpV), (iii) UVA has no effect on host–virus interactions. Our results show UVB to be a potentially important factor in the regulation of virus–host interactions in surface waters.

  • Effects of ultraviolet radiation on marine virus-phytoplankton interactions
    FEMS Microbiology Ecology, 2003
    Co-Authors: Stéphan Jacquet, Gunnar Bratbak
    Abstract:

    Ambient ultraviolet radiation (UVR) is harmful to many biological systems and increased UVR, due to a reduced ozone layer, may have many unforeseen consequences. Viruses are the most abundant biological particles in the sea and are thought to play an important role in the structure and functioning of aquatic ecosystems. Although an increasing number of studies have been published during the last 15 years, aquatic viral ecology is still in its infancy and little is known about the effect of environmental factors on virus life cycle and host-virus interactions. Using flow cytometry, we have investigated the effect of UVR (UVB intensity: 0.22 W m-2and UVA/UVB ratio ∼30) on five different cultured marine phytoplankton host-virus systems (CeV-Chrysochromulina ericina, EhV-Emiliania huxleyi, MpV-Micromonas pusilla, PpV-Phaeocystis pouchetii and PoV-Pyramimonas orientalis). Viruses appear to be susceptible to UV, but also they might provide some protection to their hosts. It is shown that (i) some of the investigated microalgae that have been co-cultured with viruses are less sensitive (e.g. P. pouchetii, M. pusilla) to UVB stress compared to susceptible microalgae (i.e. virus-free cultures), (ii) different viruses have different sensitivities to UVB in terms of both their abundance patterns (no effect for most of them except EhV) and infectivity (from no effect for PoV, to complete inactivation for PpV), (iii) UVA has no effect on host-virus interactions. Our results show UVB to be a potentially important factor in the regulation of virus-host interactions in surface waters. © 2003 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.

  • Isolation and characterization of a virus that infects Emiliania huxleyi (Haptophyta)
    Journal of Phycology, 2002
    Co-Authors: Tonje Castberg, Mikal Heldal, Aud Larsen, Ruthanne Sandaa, Runar Thyrhaug, James L Van Etten, Gunnar Bratbak
    Abstract:

    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.

  • Flow cytometric analysis of phytoplankton viability following viral infection
    Aquatic Microbial Ecology, 2001
    Co-Authors: Corina P D Brussaard, Runar Thyrhaug, Dominique Marie, Gunnar Bratbak
    Abstract:

    Two flow cytometric assays using physiological probes were used on the phytoplankton species Phaeocystis pouchetii and Micromonas pusilla to examine the assays' utility in detecting viral infections. Dead cells were detected using the membrane impermeant nucleic-acid dye SYTOX- Green, which stains algal cells that have lost their membrane integrity. Live cells were detected using the membrane permeant dye Calcein-AM, which is hydrolyzed by intracellular esterases into a green fluorescent charged form. We found that both assays are easy to use, are reproducible and can indeed be used as markers of the viability of individual phytoplankton cells following infection by viruses. Cell death rates up to 0.8 d -1 for P. pouchetii and 0.5 d -1 for M. pusilla were calculated. The first day postinfection, death rates determined by the Calcein-AM assay were typically twice as high as those determined by the SYTOX-Green assay. Both viability tests were found to assess the physi- ological status of noninfected P. pouchetii cells, independent of viral infection. The optimal choice of viability assay depended on the phytoplankton species studied. Compared with existing assays, the protocols described permit examination of infected phytoplankton in more detail, yielding insight into the heterogeneity of the algal population.

Nathalie Simon - One of the best experts on this subject based on the ideXlab platform.

  • ecological niche partitioning in the picoplanktonic green alga Micromonas pusilla evidence from environmental surveys using phylogenetic probes
    Environmental Microbiology, 2008
    Co-Authors: Elodie Foulon, Ramon Massana, Thierry Cariou, Fabienne Jalabert, Nathalie Simon
    Abstract:

    Summary Very few studies have analysed the niches of pelagic protist in details. This is because for most protists, both an accurate species definition and methods for routine detection and quantification of cells are lacking. The morphospecies Micromonas pusilla ,a marine unicellular green alga, is the most ubiquitous and cosmopolitan picoeukaryote described to date. This species comprises several independent genetic lineages or clades, which are not currently distin- guishable based on comparison of their morphology or biogeographical distribution. Molecular probes were used to detect and quantify the genetic clades of M. pusilla in samples from temperate, polar and tropi- cal environments in order to assess potential ecologi- cal niche partitioning. The three clades were detected in all biogeographical regions studied and were com- monly found in sympatry. Cell abundances recorded for clades A and B were high, especially at coastal stations. Clade C, when detected, was always at low abundances and is suggested to be a low-light clade. Shifts in the contribution of clades to total M. pusilla abundance were observed along environmental gra- dients, both at local and basin-wide scales. This sug- gests that the phylogenetic clades occupy specific niches and confirms the existence of cryptic species within the morphospecies M. pusilla. Parameters

  • Late summer community composition and abundance of photosynthetic picoeukaryotes in Norwegian and Barents Seas
    Limnology and Oceanography, 2005
    Co-Authors: Ramon Massana, Mikel Latasa, Céline Colson, Wenche Eikrem, Carlos Pedrós-alió, Dominique Marie, Daniel Vaulot, Nathalie Simon
    Abstract:

    We investigated marine picoeukaryotic diversity (cells ,3 mm) in samples collected in late summer 2002 at the boundary between the Norwegian, Greenland, and Barents Seas. The two main Arctic and Atlantic water masses in this region are separated by the polar front. We combined total counts of picoeukaryotes assemblages by flow cytometry and epifluorescence microscopy with taxa detection by tyramide signal amplification‐fluorescent in situ hybridization (TSAFISH) and high performance liquid chromatography (HPLC) pigment analyses. The picoeukaryotic community was primarily composed of photoautotrophs (75% of the cells on average). Members of the division Chlorophyta, in particular the species Micromonas pusilla (Butcher) Manton and Parke, were the major components in truly Arctic waters (32% of the picoeukaryotes, maximum 3,200 cells ml

  • Late summer community composition and abundance of photosynthetic picoeukaryotes in Norwegian and Barents Seas
    Limnology and Oceanography, 2005
    Co-Authors: Fabrice Not, Mikel Latasa, Céline Colson, Wenche Eikrem, Carlos Pedrós-alió, Ramon Massana, Dominique Marie, Daniel Vaulot, Nathalie Simon
    Abstract:

    We investigated marine picoeukaryotic diversity (cells < 3 mu m) in samples collected in late summer 2002 at the boundary between the Norwegian, Greenland, and Barents Seas. The two main Arctic and Atlantic water masses in this region are separated by the polar front. We combined total counts of picoeukaryotes assemblages by flow cytometry and epifluorescence microscopy with taxa detection by tyramide signal amplification-fluorescent in situ hybridization (TSA-FISH) and high performance liquid chromatography (HPLC) pigment analyses. The picoeukaryotic community was primarily composed of photoautotrophs (75% of the cells on average). Members of the division Chlorophyta, in particular the species Micromonas pusilla (Butcher) Manton and Parke, were the major components in truly Arctic waters (32% of the picoeukaryotes, maximum 3,200 cells ml(-1)). M. pusilla was also well represented in coastal waters and at the polar front (25 % of the picoeukaryotes, maximum 9, 100 cells ml(-1)). Haptophyta were prominent in more typical Atlantic waters (up to 35% of the picoeukaryotes, maximum 4,500 cells ml(-1)). Quantification of haptophyte biomass by HPLC pigment analyses and CHEMTAX, and haptophyte abundances by TSA-FISH were in good agreement. This confirms previous studies, which suggested that M. pusilla is a dominant contributor of picoeukaryotic communities in both coastal and nutrient rich environments, whereas haptophytes seem to be more important in open seawaters.

  • A single species, Micromonas pusilla (Prasinophyceae), dominates the eukaryotic picoplankton in the Western English Channel
    Applied and Environmental Microbiology, 2004
    Co-Authors: Fabrice Not, Mikel Latasa, Thierry Cariou, Dominique Marie, Daniel Vaulot, Nathalie Simon
    Abstract:

    The class Prasinophyceae (Chlorophyta) contains several photosynthetic picoeukaryotic species described from cultured isolates. The ecology of these organisms and their contributions to the picoeukaryotic community in aquatic ecosystems have received little consideration. We have designed and tested eight new 18S ribosomal DNA oligonucleotide probes specific for different Prasinophyceae clades, genera, and species. Using fluorescent in situ hybridization associated with tyramide signal amplification, these probes, along with more general probes, have been applied to samples from a marine coastal site off Roscoff (France) collected every 2 weeks between July 2000 and September 2001. The abundance of eukaryotic picoplankton remained high (>10(3) cells ml(-1)) during the sampling period, with maxima in summer (up to 2 X 10(4) cells ml(-1)), and a single green algal species, Micromonas pusilla (Prasinophyceae), dominated the community all year round. Members of the order Prasinococcales and the species Bathycoccus prasinos (Mamiellales) displayed sporadic occurrences, while the abundances of all other Prasinophyceae groups targeted remained negligible

Alexandra Z. Worden - One of the best experts on this subject based on the ideXlab platform.

  • Transcriptional responses of the marine green alga Micromonas pusilla and an infecting prasinovirus under different phosphate conditions
    Environmental Microbiology, 2018
    Co-Authors: Charles Bachy, Curtis A Suttle, Christina J. Charlesworth, Amy M. Chan, Jan F. Finke, Chee-hong Wong, Sebastian Sudek, Maureen L. Coleman, Alexandra Z. Worden
    Abstract:

    Prasinophytes are widespread marine algae for which responses to nutrient limitation and viral infection are not well understood. We studied the picoprasinophyte, Micromonas pusilla, grown under phosphate‐replete (0.65 ± 0.07 d⁻¹) and 10‐fold lower (low)‐phosphate (0.11 ± 0.04 d⁻¹) conditions, and infected by the phycodnavirus MpV‐SP1. Expression of 17% of Micromonas genes in uninfected cells differed by >1.5‐fold (q 

  • transcriptional responses of the marine green alga Micromonas pusilla and an infecting prasinovirus under different phosphate conditions
    Environmental Microbiology, 2018
    Co-Authors: Charles Bachy, Curtis A Suttle, Christina J. Charlesworth, Amy M. Chan, Jan F. Finke, Chee-hong Wong, Sebastian Sudek, Maureen L. Coleman, Alexandra Z. Worden
    Abstract:

    : Prasinophytes are widespread marine algae for which responses to nutrient limitation and viral infection are not well understood. We studied the picoprasinophyte, Micromonas pusilla, grown under phosphate-replete (0.65 ± 0.07 d-1 ) and 10-fold lower (low)-phosphate (0.11 ± 0.04 d-1 ) conditions, and infected by the phycodnavirus MpV-SP1. Expression of 17% of Micromonas genes in uninfected cells differed by >1.5-fold (q < 0.01) between nutrient conditions, with genes for P-metabolism and the uniquely-enriched Sel1-like repeat (SLR) family having higher relative transcript abundances, while phospholipid-synthesis genes were lower in low-P than P-replete. Approximately 70% (P-replete) and 30% (low-P) of cells were lysed 24 h post-infection, and expression of ≤5.8% of host genes changed relative to uninfected treatments. Host genes for CAZymes and glycolysis were activated by infection, supporting importance in viral production, which was significantly lower in slower growing (low-P) hosts. All MpV-SP1 genes were expressed, and our analyses suggest responses to differing host-phosphate backgrounds involve few viral genes, while the temporal program of infection involves many more, and is largely independent of host-phosphate background. Our study (i) identifies genes previously unassociated with nutrient acclimation or viral infection, (ii) provides insights into the temporal program of prasinovirus gene expression by hosts and (iii) establishes cell biological aspects of an ecologically important host-prasinovirus system that differ from other marine algal-virus systems.

  • identifying aspects of the post transcriptional program governing the proteome of the green alga Micromonas pusilla
    PLOS ONE, 2016
    Co-Authors: Peter Waltman, Chee-hong Wong, Emily Nahas Reistetter, Samuel O Purvine, Charles Ansong, Marijke J Van Baren, Richard D Smith, Stephen J Callister, Joshua M Stuart, Alexandra Z. Worden
    Abstract:

    Micromonas is a unicellular motile alga within the Prasinophyceae, a green algal group that is related to land plants. This picoeukaryote (<2 μm diameter) is widespread in the marine environment but is not well understood at the cellular level. Here, we examine shifts in mRNA and protein expression over the course of the day-night cycle using triplicated mid-exponential, nutrient replete cultures of Micromonas pusilla CCMP1545. Samples were collected at key transition points during the diel cycle for evaluation using high-throughput LC-MS proteomics. In conjunction, matched mRNA samples from the same time points were sequenced using pair-ended directional Illumina RNA-Seq to investigate the dynamics and relationship between the mRNA and protein expression programs of M. pusilla. Similar to a prior study of the marine cyanobacterium Prochlorococcus, we found significant divergence in the mRNA and proteomics expression dynamics in response to the light:dark cycle. Additionally, expressional responses of genes and the proteins they encoded could also be variable within the same metabolic pathway, such as we observed in the oxygenic photosynthesis pathway. A regression framework was used to predict protein levels from both mRNA expression and gene-specific sequence-based features. Several features in the genome sequence were found to influence protein abundance including codon usage as well as 3' UTR length and structure. Collectively, our studies provide insights into the regulation of the proteome over a diel cycle as well as the relationships between transcriptional and translational programs in the widespread marine green alga Micromonas.

  • Early Gene Duplication Within Chloroplastida and Its Correspondence With Relocation of Starch Metabolism to Chloroplasts
    Genetics, 2008
    Co-Authors: Philippe Deschamps, Alexandra Z. Worden, Hervé Moreau, David Dauvillée, Steven G. Ball
    Abstract:

    The endosymbiosis event resulting in the plastid of photosynthetic eukaryotes was accompanied by the appearance of a novel form of storage polysaccharide in Rhodophyceae, Glaucophyta, and Chloroplastida. Previous analyses indicated that starch synthesis resulted from the merging of the cyanobacterial and the eukaryotic storage polysaccharide metabolism pathways. We performed a comparative bioinformatic analysis of six algal genome sequences to investigate this merger. Specifically, we analyzed two Chlorophyceae, Chlamydomonas reinhardtii and Volvox carterii, and four Prasinophytae, two Ostreococcus strains and two Micromonas pusilla strains. Our analyses revealed a complex metabolic pathway whose intricacies and function seem conserved throughout the green lineage. Comparison of this pathway to that recently proposed for the Rhodophyceae suggests that the complexity that we observed is unique to the green lineage and was generated when the latter diverged from the red algae. This finding corresponds well with the plastidial location of starch metabolism in Chloroplastidae. In contrast, Rhodophyceae and Glaucophyta produce and store starch in the cytoplasm and have a lower complexity pathway. Cytoplasmic starch synthesis is currently hypothesized to represent the ancestral state of storage polysaccharide metabolism in Archaeplastida. The retargeting of components of the cytoplasmic pathway to plastids likely required a complex stepwise process involving several rounds of gene duplications. We propose that this relocation of glucan synthesis to the plastid facilitated evolution of chlorophyll-containing light-harvesting complex antennae by playing a protective role within the chloroplast.