The Experts below are selected from a list of 4986 Experts worldwide ranked by ideXlab platform

William H Wilson - One of the best experts on this subject based on the ideXlab platform.

  • Targeted sorting of single virus-infected cells of the coccolithophore Emiliania huxleyi.
    PLOS ONE, 2011
    Co-Authors: Joaquin Martinez Martinez, Nicole J. Poulton, Ramunas Stepanauskas, Michael E. Sieracki, William H Wilson
    Abstract:

    Discriminating infected from healthy cells is the first step to understanding the mechanisms and ecological implications of viral infection. We have developed a method for detecting, sorting, and performing molecular analysis of individual, infected cells of the important microalga Emiliania huxleyi, based on known physiological responses to viral infection. Of three fluorescent dyes tested, FM 1-43 (for detecting membrane blebbing) gave the most unequivocal and earliest separation of cells. Furthermore, we were able to amplify the genomes of single infected cells using Multiple Displacement Amplification. This novel method to reliably discriminate infected from healthy cells in cultures will allow researchers to answer numerous questions regarding the mechanisms and implications of viral infection of E. huxleyi. The method may be transferable to other virus-host systems.

  • the cheshire cat escape strategy of the coccolithophore Emiliania huxleyi in response to viral infection
    Proceedings of the National Academy of Sciences of the United States of America, 2008
    Co-Authors: Miguel Frada, Michael J. Allen, William H Wilson, Ian Probert, Colomban De Vargas
    Abstract:

    The coccolithophore Emiliania huxleyi is one of the most successful eukaryotes in modern oceans. The two phases in its haplodiploid life cycle exhibit radically different phenotypes. The diploid calcified phase forms extensive blooms, which profoundly impact global biogeochemical equilibria. By contrast, the ecological role of the noncalcified haploid phase has been completely overlooked. Giant phycodnaviruses (Emiliania huxleyi viruses, EhVs) have been shown to infect and lyse diploid-phase cells and to be heavily implicated in the regulation of populations and the termination of blooms. Here, we demonstrate that the haploid phase of E. huxleyi is unrecognizable and therefore resistant to EhVs that kill the diploid phase. We further show that exposure of diploid E. huxleyi to EhVs induces transition to the haploid phase. Thus we have clearly demonstrated a drastic difference in viral susceptibility between life cycle stages with different ploidy levels in a unicellular eukaryote. Resistance of the haploid phase of E. huxleyi provides an escape mechanism that involves separation of meiosis from sexual fusion in time, thus ensuring that genes of dominant diploid clones are passed on to the next generation in a virus-free environment. These “Cheshire Cat” ecological dynamics release host evolution from pathogen pressure and thus can be seen as an opposite force to a classic “Red Queen” coevolutionary arms race. In E. huxleyi, this phenomenon can account for the fact that the selective balance is tilted toward the boom-and-bust scenario of optimization of both growth rates of calcifying E. huxleyi cells and infectivity of EhVs.

  • The response of carotenoids and chlorophylls during virus infection of Emiliania huxleyi (Prymnesiophyceae)
    Journal of Experimental Marine Biology and Ecology, 2007
    Co-Authors: Carole A. Llewellyn, Ruth L. Airs, Nicole J. Bale, Claire Evans, Isobel Cook, William H Wilson
    Abstract:

    We report the response of carotenoids and chlorophylls during 120 h time series virus infection experiments of the marine coccolithophorid Emiliania huxleyi (Lohm.) Hay et Mohler culture. The response of individual carotenoids to infection varied: Diatoxanthin (Dtx) increased rapidly relative to chlorophyll-a, whereas diadinoxanthin (Ddx) and β-carotene showed a rapid decrease and fucoxanthin and 19′hexanoyloxyfucoxanthin a slight increase. The response of the individual carotenoids reflects their role in epoxy/de-epoxidation cycling, antioxidant protection, biosynthetic conversion and vulnerability to photooxidative destruction. We observed for the first time the operation of the diadinoxanthin cycle occurring in response to viral infection in E. huxleyi with the de-epoxidation ratio (Dtx / (Dtx + Ddx)) increasing exponentially with time (R2 = 0.92) and decreasing exponentially with FV / FM (R2 = 0.97). Our findings contribute to our understanding of the conversion and fate of key biochemical cell constituents in algae and are important in understanding the physiological stress response to virus infection.

  • a genetic marker to separate Emiliania huxleyi prymnesiophyceae morphotypes
    Journal of Phycology, 2005
    Co-Authors: Declan C. Schroeder, Matthew J. Hall, Gillian Malin, Gaia F Biggi, Joanne E Davy, Joaquin Martinez Martinez, Anthony J Richardson, William H Wilson
    Abstract:

    Emiliania huxleyi (Lohm.) Hay and Mohler is a ubiquitous unicellular marine alga surrounded by an elaborate covering of calcite platelets called coccoliths. It is an important primary producer involved in oceanic biogeochemistry and climate regulation. Currently, E. huxleyi is separated into five morphotypes based on morphometric, physiological, biochemical, and immunological differences. However, a genetic marker has yet to be found to characterize these morphotypes. With the use of sequence analysis and denaturing gradient gel electrophoresis, we discovered a genetic marker that correlates significantly with the separation of the most widely recognized A and B morphotypes. Furthermore, we reveal that the A morphotype is composed of a number of distinct genotypes. This marker lies within the 3' untranslated region of a coccolith associated protein mRNA, which is implicated in regulating coccolith calcification. Consequently, we tentatively termed this marker the coccolith morphology motif.

  • virus succession observed during an Emiliania huxleyi bloom
    Applied and Environmental Microbiology, 2003
    Co-Authors: Declan C. Schroeder, Matthew J. Hall, Gillian Malin, William H Wilson
    Abstract:

    Denaturing gradient gel electrophoresis was used as a molecular tool to determine the diversity and to monitor population dynamics of viruses that infect the globally important coccolithophorid Emiliania huxleyi. We exploited variations in the major capsid protein gene from E. huxleyi-specific viruses to monitor their genetic diversity during an E. huxleyi bloom in a mesocosm experiment off western Norway. We reveal that, despite the presence of several virus genotypes at the start of an E. huxleyi bloom, only a few virus genotypes eventually go on to kill the bloom.

Benjamin A S Van Mooy - One of the best experts on this subject based on the ideXlab platform.

  • Alkenone unsaturation during virus infection of Emiliania huxleyi
    Organic Geochemistry, 2017
    Co-Authors: James M Fulton, Giacomo R Ditullio, B. Jacob Kendrick, Benjamin A S Van Mooy
    Abstract:

    Abstract Alkenones are found in diverse prymnesiophytes including Emiliania huxleyi , which ranges throughout the world ocean. The number of double bonds in alkenones corresponds with growth temperature, and calibrations between sea surface temperature and alkenone unsaturation have been used to establish alkenone unsaturation as a temperature proxy in ancient sediments. Here we report virus infection causes a relative increase in the proportion of diunsaturated alkenones in E. huxleyi strain CCMP 374. As virus infection routinely terminates E. huxleyi blooms in the ocean, it is possible that this contributes to the variance in alkenone-based temperature estimates for core-top sediments.

  • phosphorus starvation induces membrane remodeling and recycling in Emiliania huxleyi
    New Phytologist, 2016
    Co-Authors: Adva Shemi, Benjamin A S Van Mooy, Helen F Fredricks, Daniella Schatz, Ziv Porat, Assaf Vardi
    Abstract:

    Summary Nutrient availability is an important factor controlling phytoplankton productivity. Phytoplankton contribute c. 50% of the global photosynthesis and possess efficient acclimation mechanisms to cope with nutrient stress. We investigate the cellular response of the bloom-forming coccolithophore Emiliania huxleyi to phosphorus (P) scarcity, which is often a limiting factor in marine ecosystems. We combined mass spectrometry, fluorescence microscopy, transmission electron microscopy (TEM) and gene expression analyses in order to assess diverse cellular features in cells exposed to P limitation and recovery. Early starvation-induced substitution of phospholipids in the cells' membranes with galacto- and betaine lipids. Lipid remodeling was rapid and reversible upon P resupply. The PI3K inhibitor wortmannin reduced phospholipid substitution, suggesting a possible involvement of PI3K- signaling in this process. In addition, P limitation enhanced the formation and acidification of membrane vesicles in the cytoplasm. Intracellular vesicles may facilitate the recycling of cytoplasmic content, which is engulfed in the vesicles and delivered to the main vacuole. Long-term starvation was characterized by a profound increase in cell size and morphological alterations in cellular ultrastructure. This study provides cellular and molecular basis for future ecophysiological assessment of natural E. huxleyi populations in oligotrophic regions.

  • temperature induced viral resistance in Emiliania huxleyi prymnesiophyceae
    PLOS ONE, 2014
    Co-Authors: Jacob B Kendrick, Giacomo R Ditullio, Tyler Cyronak, James M Fulton, Benjamin A S Van Mooy, Kay D Bidle
    Abstract:

    Annual Emiliania huxleyi blooms (along with other coccolithophorid species) play important roles in the global carbon and sulfur cycles. E. huxleyi blooms are routinely terminated by large, host-specific dsDNA viruses, (Emiliania huxleyi Viruses; EhVs), making these host-virus interactions a driving force behind their potential impact on global biogeochemical cycles. Given projected increases in sea surface temperature due to climate change, it is imperative to understand the effects of temperature on E. huxleyi’s susceptibility to viral infection and its production of climatically active dimethylated sulfur species (DSS). Here we demonstrate that a 3°C increase in temperature induces EhV-resistant phenotypes in three E. huxleyi strains and that successful virus infection impacts DSS pool sizes. We also examined cellular polar lipids, given their documented roles in regulating host-virus interactions in this system, and propose that alterations to membrane-bound surface receptors are responsible for the observed temperature-induced resistance. Our findings have potential implications for global biogeochemical cycles in a warming climate and for deciphering the particular mechanism(s) by which some E. huxleyi strains exhibit viral resistance.

  • novel molecular determinants of viral susceptibility and resistance in the lipidome of Emiliania huxleyi
    Environmental Microbiology, 2014
    Co-Authors: James M Fulton, Jacob B Kendrick, Giacomo R Ditullio, Kay D Bidle, Helen F Fredricks, Assaf Vardi, Benjamin A S Van Mooy
    Abstract:

    Summary Viruses play a key role in controlling the population dynamics of algae, including Emiliania huxleyi, a globally distributed haptophyte with calcite coccoliths that comprise ca. 50% of the sinking carbonate flux from the surface ocean. Emiliania huxleyi viruses (EhVs) routinely infect and terminate E. huxleyi blooms. EhVs are surrounded by a lipid envelope, which we found to be comprised largely of glycosphingolipids (GSLs) with lesser amounts of polar glycerolipids. Infection appears to involve membrane fusion between the virus and host, and we hypothesized that specific polar lipids may facilitate virus attachment. We identified three novel intact polar lipids in E. huxleyi strain CCMP 374 and EhV86, including a GSL with a monosaccharide sialic acid headgroup (sGSL); for all 11 E. huxleyi strains we tested, there was a direct relationship between sGSL content and sensitivity to infection by EhV1, EhV86 and EhV163. In mesocosms, the E. huxleyi population with greatest initial sGSL content had the highest rate of virus-induced mortality. We propose potential physiological roles for sGSL that would be beneficial for growth but leave cells susceptible to infection, thus furthering the discussion of Red Queen-based co-evolution and the cost(s) of sensitivity and resistance in the dynamic E. huxleyi-EhV system.

James M Fulton - One of the best experts on this subject based on the ideXlab platform.

  • Alkenone unsaturation during virus infection of Emiliania huxleyi
    Organic Geochemistry, 2017
    Co-Authors: James M Fulton, Giacomo R Ditullio, B. Jacob Kendrick, Benjamin A S Van Mooy
    Abstract:

    Abstract Alkenones are found in diverse prymnesiophytes including Emiliania huxleyi , which ranges throughout the world ocean. The number of double bonds in alkenones corresponds with growth temperature, and calibrations between sea surface temperature and alkenone unsaturation have been used to establish alkenone unsaturation as a temperature proxy in ancient sediments. Here we report virus infection causes a relative increase in the proportion of diunsaturated alkenones in E. huxleyi strain CCMP 374. As virus infection routinely terminates E. huxleyi blooms in the ocean, it is possible that this contributes to the variance in alkenone-based temperature estimates for core-top sediments.

  • temperature induced viral resistance in Emiliania huxleyi prymnesiophyceae
    PLOS ONE, 2014
    Co-Authors: Jacob B Kendrick, Giacomo R Ditullio, Tyler Cyronak, James M Fulton, Benjamin A S Van Mooy, Kay D Bidle
    Abstract:

    Annual Emiliania huxleyi blooms (along with other coccolithophorid species) play important roles in the global carbon and sulfur cycles. E. huxleyi blooms are routinely terminated by large, host-specific dsDNA viruses, (Emiliania huxleyi Viruses; EhVs), making these host-virus interactions a driving force behind their potential impact on global biogeochemical cycles. Given projected increases in sea surface temperature due to climate change, it is imperative to understand the effects of temperature on E. huxleyi’s susceptibility to viral infection and its production of climatically active dimethylated sulfur species (DSS). Here we demonstrate that a 3°C increase in temperature induces EhV-resistant phenotypes in three E. huxleyi strains and that successful virus infection impacts DSS pool sizes. We also examined cellular polar lipids, given their documented roles in regulating host-virus interactions in this system, and propose that alterations to membrane-bound surface receptors are responsible for the observed temperature-induced resistance. Our findings have potential implications for global biogeochemical cycles in a warming climate and for deciphering the particular mechanism(s) by which some E. huxleyi strains exhibit viral resistance.

  • novel molecular determinants of viral susceptibility and resistance in the lipidome of Emiliania huxleyi
    Environmental Microbiology, 2014
    Co-Authors: James M Fulton, Jacob B Kendrick, Giacomo R Ditullio, Kay D Bidle, Helen F Fredricks, Assaf Vardi, Benjamin A S Van Mooy
    Abstract:

    Summary Viruses play a key role in controlling the population dynamics of algae, including Emiliania huxleyi, a globally distributed haptophyte with calcite coccoliths that comprise ca. 50% of the sinking carbonate flux from the surface ocean. Emiliania huxleyi viruses (EhVs) routinely infect and terminate E. huxleyi blooms. EhVs are surrounded by a lipid envelope, which we found to be comprised largely of glycosphingolipids (GSLs) with lesser amounts of polar glycerolipids. Infection appears to involve membrane fusion between the virus and host, and we hypothesized that specific polar lipids may facilitate virus attachment. We identified three novel intact polar lipids in E. huxleyi strain CCMP 374 and EhV86, including a GSL with a monosaccharide sialic acid headgroup (sGSL); for all 11 E. huxleyi strains we tested, there was a direct relationship between sGSL content and sensitivity to infection by EhV1, EhV86 and EhV163. In mesocosms, the E. huxleyi population with greatest initial sGSL content had the highest rate of virus-induced mortality. We propose potential physiological roles for sGSL that would be beneficial for growth but leave cells susceptible to infection, thus furthering the discussion of Red Queen-based co-evolution and the cost(s) of sensitivity and resistance in the dynamic E. huxleyi-EhV system.

Declan C. Schroeder - One of the best experts on this subject based on the ideXlab platform.

  • dissecting the impact of co2 and ph on the mechanisms of photosynthesis and calcification in the coccolithophore Emiliania huxleyi
    New Phytologist, 2013
    Co-Authors: Lennart T Bach, Declan C. Schroeder, Luke C M Mackinder, Kai G Schulz, Glen L Wheeler, Colin Brownlee, Ulf Riebesell
    Abstract:

    Coccolithophores are important calcifying phytoplankton predicted to be impacted by changes in ocean carbonate chemistry caused by the absorption of anthropogenic CO2. However, it is difficult to disentangle the effects of the simultaneously changing carbonate system parameters (CO2, bicarbonate, carbonate and protons) on the physiological responses to elevated CO2. Here, we adopted a multifactorial approach at constant pH or CO2 whilst varying dissolved inorganic carbon (DIC) to determine physiological and transcriptional responses to individual carbonate system parameters. We show that Emiliania huxleyi is sensitive to low CO2 (growth and photosynthesis) and low bicarbonate (calcification) as well as low pH beyond a limited tolerance range, but is much less sensitive to elevated CO2 and bicarbonate. Multiple up-regulated genes at low DIC bear the hallmarks of a carbon-concentrating mechanism (CCM) that is responsive to CO2 and bicarbonate but not to pH. Emiliania huxleyi appears to have evolved mechanisms to respond to limiting rather than elevated CO2. Calcification does not function as a CCM, but is inhibited at low DIC to allow the redistribution of DIC from calcification to photosynthesis. The presented data provides a significant step in understanding how E. huxleyi will respond to changing carbonate chemistry at a cellular level.

  • expression of biomineralization related ion transport genes in Emiliania huxleyi
    Environmental Microbiology, 2011
    Co-Authors: Luke C M Mackinder, Declan C. Schroeder, Ulf Riebesell, Glen L Wheeler, Peter Von Dassow, Colin Brownlee
    Abstract:

    Biomineralization in the marine phytoplankton Emiliania huxleyi is a stringently controlled intracellular process. The molecular basis of coccolith production is still relatively unknown although its importance in global biogeochemical cycles and varying sensitivity to increased pCO2 levels has been well documented. This study looks into the role of several candidate Ca2+, H+ and inorganic carbon transport genes in E. huxleyi, using quantitative reverse transcriptase PCR. Differential gene expression analysis was investigated in two isogenic pairs of calcifying and non-calcifying strains of E. huxleyi and cultures grown at various Ca2+ concentrations to alter calcite production. We show that calcification correlated to the consistent upregulation of a putative HCO3- transporter belonging to the solute carrier 4 (SLC4) family, a Ca2+/H+ exchanger belonging to the CAX family of exchangers and a vacuolar H+-ATPase. We also show that the coccolith-associated protein, GPA is downregulated in calcifying cells. The data provide strong evidence that these genes play key roles in E. huxleyi biomineralization. Based on the gene expression data and the current literature a working model for biomineralization-related ion transport in coccolithophores is presented.

  • Novel virus dynamics in an Emiliania huxleyi bloom
    Journal of Plankton Research, 2009
    Co-Authors: George Sorensen, Andrea C. Baker, Matthew J. Hall, Colin B. Munn, Declan C. Schroeder
    Abstract:

    Diel studies of an Emiliania huxleyi bloom within a mesocosm revealed a highly dynamic associated viral community, changing on small times scales of hours.

  • a genetic marker to separate Emiliania huxleyi prymnesiophyceae morphotypes
    Journal of Phycology, 2005
    Co-Authors: Declan C. Schroeder, Matthew J. Hall, Gillian Malin, Gaia F Biggi, Joanne E Davy, Joaquin Martinez Martinez, Anthony J Richardson, William H Wilson
    Abstract:

    Emiliania huxleyi (Lohm.) Hay and Mohler is a ubiquitous unicellular marine alga surrounded by an elaborate covering of calcite platelets called coccoliths. It is an important primary producer involved in oceanic biogeochemistry and climate regulation. Currently, E. huxleyi is separated into five morphotypes based on morphometric, physiological, biochemical, and immunological differences. However, a genetic marker has yet to be found to characterize these morphotypes. With the use of sequence analysis and denaturing gradient gel electrophoresis, we discovered a genetic marker that correlates significantly with the separation of the most widely recognized A and B morphotypes. Furthermore, we reveal that the A morphotype is composed of a number of distinct genotypes. This marker lies within the 3' untranslated region of a coccolith associated protein mRNA, which is implicated in regulating coccolith calcification. Consequently, we tentatively termed this marker the coccolith morphology motif.

  • virus succession observed during an Emiliania huxleyi bloom
    Applied and Environmental Microbiology, 2003
    Co-Authors: Declan C. Schroeder, Matthew J. Hall, Gillian Malin, William H Wilson
    Abstract:

    Denaturing gradient gel electrophoresis was used as a molecular tool to determine the diversity and to monitor population dynamics of viruses that infect the globally important coccolithophorid Emiliania huxleyi. We exploited variations in the major capsid protein gene from E. huxleyi-specific viruses to monitor their genetic diversity during an E. huxleyi bloom in a mesocosm experiment off western Norway. We reveal that, despite the presence of several virus genotypes at the start of an E. huxleyi bloom, only a few virus genotypes eventually go on to kill the bloom.

Ulf Riebesell - One of the best experts on this subject based on the ideXlab platform.

  • functional genetic divergence in high co2 adapted Emiliania huxleyi populations
    Evolution, 2013
    Co-Authors: Kai T Lohbeck, Ulf Riebesell, Sinead Collins, Thorsten B H Reusch
    Abstract:

    Predicting the impacts of environmental change on marine organisms, food webs, and biogeochemical cycles presently relies almost exclusively on short-term physiological studies, while the possibility of adaptive evolution is often ignored. Here, we assess adaptive evolution in the coccolithophore Emiliania huxleyi, a well-established model species in biological oceanography, in response to ocean acidification. We previously demonstrated that this globally important marine phytoplankton species adapts within 500 generations to elevated CO2. After 750 and 1000 generations, no further fitness increase occurred, and we observed phenotypic convergence between replicate populations. We then exposed adapted populations to two novel environments to investigate whether or not the underlying basis for high CO2-adaptation involves functional genetic divergence, assuming that different novel mutations become apparent via divergent pleiotropic effects. The novel environment “high light” did not reveal such genetic divergence whereas growth in a low-salinity environment revealed strong pleiotropic effects in high CO2 adapted populations, indicating divergent genetic bases for adaptation to high CO2. This suggests that pleiotropy plays an important role in adaptation of natural E. huxleyi populations to ocean acidification. Our study highlights the potential mutual benefits for oceanography and evolutionary biology of using ecologically important marine phytoplankton for microbial evolution experiments.

  • dissecting the impact of co2 and ph on the mechanisms of photosynthesis and calcification in the coccolithophore Emiliania huxleyi
    New Phytologist, 2013
    Co-Authors: Lennart T Bach, Declan C. Schroeder, Luke C M Mackinder, Kai G Schulz, Glen L Wheeler, Colin Brownlee, Ulf Riebesell
    Abstract:

    Coccolithophores are important calcifying phytoplankton predicted to be impacted by changes in ocean carbonate chemistry caused by the absorption of anthropogenic CO2. However, it is difficult to disentangle the effects of the simultaneously changing carbonate system parameters (CO2, bicarbonate, carbonate and protons) on the physiological responses to elevated CO2. Here, we adopted a multifactorial approach at constant pH or CO2 whilst varying dissolved inorganic carbon (DIC) to determine physiological and transcriptional responses to individual carbonate system parameters. We show that Emiliania huxleyi is sensitive to low CO2 (growth and photosynthesis) and low bicarbonate (calcification) as well as low pH beyond a limited tolerance range, but is much less sensitive to elevated CO2 and bicarbonate. Multiple up-regulated genes at low DIC bear the hallmarks of a carbon-concentrating mechanism (CCM) that is responsive to CO2 and bicarbonate but not to pH. Emiliania huxleyi appears to have evolved mechanisms to respond to limiting rather than elevated CO2. Calcification does not function as a CCM, but is inhibited at low DIC to allow the redistribution of DIC from calcification to photosynthesis. The presented data provides a significant step in understanding how E. huxleyi will respond to changing carbonate chemistry at a cellular level.

  • expression of biomineralization related ion transport genes in Emiliania huxleyi
    Environmental Microbiology, 2011
    Co-Authors: Luke C M Mackinder, Declan C. Schroeder, Ulf Riebesell, Glen L Wheeler, Peter Von Dassow, Colin Brownlee
    Abstract:

    Biomineralization in the marine phytoplankton Emiliania huxleyi is a stringently controlled intracellular process. The molecular basis of coccolith production is still relatively unknown although its importance in global biogeochemical cycles and varying sensitivity to increased pCO2 levels has been well documented. This study looks into the role of several candidate Ca2+, H+ and inorganic carbon transport genes in E. huxleyi, using quantitative reverse transcriptase PCR. Differential gene expression analysis was investigated in two isogenic pairs of calcifying and non-calcifying strains of E. huxleyi and cultures grown at various Ca2+ concentrations to alter calcite production. We show that calcification correlated to the consistent upregulation of a putative HCO3- transporter belonging to the solute carrier 4 (SLC4) family, a Ca2+/H+ exchanger belonging to the CAX family of exchangers and a vacuolar H+-ATPase. We also show that the coccolith-associated protein, GPA is downregulated in calcifying cells. The data provide strong evidence that these genes play key roles in E. huxleyi biomineralization. Based on the gene expression data and the current literature a working model for biomineralization-related ion transport in coccolithophores is presented.

  • Short-term response of the coccolithophore Emiliania huxleyi to an abrupt change in seawater carbon dioxide concentrations.
    Biogeosciences, 2009
    Co-Authors: J. Barcelos E Ramos, Marius N Muller, Ulf Riebesell
    Abstract:

    The response of the coccolithophore Emiliania huxleyi to rising CO2 concentrations is well documented for acclimated cultures where cells are exposed to the CO2 treatments for several generations prior to the experiment. The exact number of generations required for acclimation to CO2-induced changes in seawater carbonate chemistry, however, is unknown. Here we show that Emiliania hux- leyi's short-term response (26 h) after cultures (grown at 500 µatm) were abruptly exposed to changed CO2 concentra- tions ( 190, 410, 800 and 1500 µatm) is similar to that ob- tained with acclimated cultures under comparable conditions in earlier studies. Most importantly, from the lower CO2 lev- els (190 and 410 µatm) to 750 and 1500 µatm calcification de- creased and organic carbon fixation increased within the first 8 to 14 h after exposing the cultures to changes in carbonate chemistry. This suggests that Emiliania huxleyi rapidly al- ters the rates of essential metabolical processes in response to changes in seawater carbonate chemistry, establishing a new physiological "state" (acclimation) within a matter of hours. If this relatively rapid response applies to other phy- toplankton species, it may simplify interpretation of studies with natural communities (e.g. mesocosm studies and ship- board incubations), where often it is not feasible to allow for a pre-conditioning phase before starting experimental incu- bations.

  • cellular calcium pathways and isotope fractionation in Emiliania huxleyi
    Geology, 2006
    Co-Authors: Nikolaus Gussone, Gerald Langer, Gernot Nehrke, Silke Thoms, Ulf Riebesell, Anton Eisenhauer, Gerold Wefer
    Abstract:

    The marine calcifying algae Emiliania huxleyi (coccolithophores) was grown in laboratory cultures under varying conditions with respect to the environmental parameters of temperature and carbonate ion concentration [CO32-] concentration. The Ca isotope composition of E. huxleyi's coccoliths reveals new insights into fractionation processes during biomineralization. The temperature-dependent Ca isotope fractionation resembles previous calibrations of inorganic and biogenic calcite and aragonite. Unlike inorganically precipitated calcite, the [CO32-] concentration of the medium has no significant effect on the Ca isotope composition of the coccoliths. These results indicate a decoupling of the chemical properties of the bulk medium and the calcifying vesicle. Cellular Ca pathways of E. huxleyi indicate that fractionation cannot occur at the crystal surface, as occurs during inorganic precipitation. The dominant processes leading to the observed Ca isotope fractionation pattern in E. huxleyi are most likely the dehydration of the Ca aquocomplex at the plasma membrane and the attachment of dissolved Ca to proteins of Ca channels. The independence of Ca isotope fractionation from [CO32-] and the small temperature dependence of E. huxleyi are also important for defining the isotopic signature of the oceanic Ca sink. Since coccolithophores contribute to about half the global CaCO3 production, a relatively uniform isotopic composition of the oceanic Ca sink is further supported.