Emiliania Huxleyi Research Articles

Cocolitoforos en sedimentos marinos frente a la entrada occidental del Estrecho de Magallanes (53S) revelan cam-bios en la productividad durante los ultimos 30.000 anos

We present a new record of coccolithophore (coccoliths) export productivity for the past 30,000 years based on the study of a marine sediment core collected at the western entrance of the Strait of Magellan (Core MD07-3128; 53°S, 75oW). This sediment core revealed the presence of an assemblage composed by thirteen coccolithophore taxa, dominated by small Gephyrocapsa (>80% of the total assemblage on the average) and accompanied, in less proportions (1-10%), by two morphotypes of Emiliana huxleyi, Coccolithus pelagicus and Calcidiscus leptoporus. Coccolith concentration and CaCO3 content were strongly correlated (P 30%) and coccolith abundance (~10 9 coccoliths g -1 dry sediment) coincided with relatively warm periods (e.g., the Holocene). We found marked differences when comparing our data with a coccolith record published by Saavedra-Pellitero et al. (2011) for ODP Site 1233 at 41°S: At ODP Site 1233, coccolithophore production was maximal during the Last Glacial Maximum in response to the northward advection of macronutrients by the Antarctic Circumpolar Current. In contrast, site MD07-3128 experienced a reduction in coccolithophore production at the time, probably related to the negative effect exerted by the high inputs of terrigenous material and meltwater from the then nearby located large Patagonian Ice Sheet.

Chemical and mass spectrometry characterization of the red alga Pyropia yezoensis chemoprotective protein (PYP): protective activity of the N-terminal fragment of PYP1 against acetaminophen-induced cell death in Chang liver cells.

In the present study, the chemical structure and chemoprotective activity of Pyropia yezoensis protein (PYP) were investigated using sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, automated protein sequencing, matrix-assisted laser desorption/ionization-quadrupole ion trap-time-of-flight mass spectrometry and a chemoprotective assay using a synthetic peptide. The PYP fraction was demonstrated to contain two proteins: PYP1 (10 kDa, SDS-resistant dimer) and PYP2 (10 kDa). PYP1 is a novel protein showing sequence homology with the hypothetical function-unknown proteins of Chondrus crispus (Rhodophyta) and Emiliania huxleyi (Haptophyceae). PYP2 is a paralog of an extrinsic protein of photosystem II found in other Rhodophyta. The synthetic peptide PYP1 (1-20), corresponding to the N-terminal 20 residues of PYP1 (ALEGGKSSGGGEATRDPEPT), exhibits chemoprotective activity against acetaminophen-induced cell death in Chang liver cells, indicating that PYP1 is a chemoprotectant of the PYP fraction. A possible association between the structure of PYP and its chemoprotective activity is discussed.

Zooplankton May Serve as Transmission Vectors for Viruses Infecting Algal Blooms in the Ocean

Marine viruses are recognized as a major driving force regulating phytoplankton community composition and nutrient cycling in the oceans. Yet, little is known about mechanisms that influence viral dispersal in aquatic systems, other than physical processes, and that lead to the rapid demise of large-scale algal blooms in the oceans. Here, we show that copepods, abundant migrating crustaceans that graze on phytoplankton, as well as other zooplankton can accumulate and mediate the transmission of viruses infecting Emiliania huxleyi, a bloom-forming coccolithophore that plays an important role in the carbon cycle. We detected by PCR that >80% of copepods collected during a North Atlantic E. huxleyi bloom carried E. huxleyi virus (EhV) DNA. We demonstrated by isolating a new infectious EhV strain from a copepod microbiome that these viruses are infectious. We further showed that EhVs can accumulate in high titers within zooplankton guts during feeding or can be adsorbed to their surface. Subsequently, EhV can be dispersed by detachment or via viral-dense fecal pellets over a period of 1 day postfeeding on EhV-infected algal cells, readily infecting new host populations. Intriguingly, the passage through zooplankton guts prolonged EhV's half-life of infectivity by 35%, relative to free virions in seawater, potentially enhancing viral transmission. We propose that zooplankton, swimming through topographically adjacent phytoplankton micropatches and migrating daily over large areas across physically separated water masses, can serve as viral vectors, boosting host-virus contact rates and potentially accelerating the demise of large-scale phytoplankton blooms.

Hybrid biosynthesis of roseobacticides from algal and bacterial precursor molecules.

Roseobacticides regulate the symbiotic relationship between a marine bacterium (Phaeobacter inhibens) and a marine microalga (Emiliania huxleyi). This relationship can be mutualistic, when the algal host provides food for the bacteria and the bacteria produce growth hormones and antibiotics for the algae, or parasitic, when the algae senesce and release p-coumaric acid. The released p-coumaric acid causes the bacteria to synthesize roseobacticides, which are nM−μM toxins for the algae. We examined the biosynthesis of roseobacticides and report that all roseobacticide precursors play critical roles during the mutualist phase of the symbiosis. Roseobacticides are biosynthesized from the algal growth promoter, the major food molecule provided by the algal cells, and the algal senescence signal that initiates the mutualist-to-parasite switch. Thus, molecules that are beneficial during mutualism are diverted to the synthesis of toxins during parasitism. A plausible mechanism for assembling roseobacticides from these molecules is proposed.

Isotopic discrimination and kinetic parameters of RubisCO from the marine bloom-forming diatom, Skeletonema costatum.

The cosmopolitan, bloom-forming diatom, Skeletonema costatum, is a prominent primary producer in coastal oceans, fixing CO2 with ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) that is phylogenetically distinct from terrestrial plant RubisCO. RubisCOs are subdivided into groups based on sequence similarity of their large subunits (IA-ID, II, and III). ID is present in several major oceanic primary producers, including diatoms such as S. costatum, coccolithophores, and some dinoflagellates, and differs substantially in amino acid sequence from the well-studied IB enzymes present in most cyanobacteria and in green algae and plants. Despite this sequence divergence, and differences in isotopic discrimination apparent in other RubisCO enzymes, stable carbon isotope compositions of diatoms and other marine phytoplankton are generally interpreted assuming enzymatic isotopic discrimination similar to spinach RubisCO (IB). To interpret phytoplankton δ(13) C values, S. costatum RubisCO was characterized via sequence analysis, and measurement of its KCO2 and Vmax , and degree of isotopic discrimination. The sequence of this enzyme placed it among other diatom ID RubisCOs. Michaelis-Menten parameters were similar to other ID enzymes (KCO2 = 48.9 ± 2.8 μm; Vmax = 165.1 ± 6.3 nmol min(-1 ) mg(-1) ). However, isotopic discrimination (ε = [(12) k/(13) k - 1] × 1000) was low (18.5‰; 17.0-19.9, 95% CI) when compared to IA and IB RubisCOs (22-29‰), though not as low as ID from coccolithophore, Emiliania huxleyi (11.1‰). Variability in ε-values among RubisCOs from primary producers is likely reflected in δ(13) C values of oceanic biomass. Currently, δ(13) C variability is ascribed to physical or chemical factors (e.g. illumination, nutrient availability) and physiological responses to these factors (e.g. carbon-concentrating mechanisms). Estimating the importance of these factors from δ(13) C measurements requires an accurate ε-value, and a mass-balance model using the ε-value for S. costatum RubisCO is presented. Clearly, appropriate ε-values must be included in interpreting δ(13) C values of environmental samples.

Emiliania huxleyi population growth rate response to light and temperature: a synthesis

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 73:163-170 (2014) - DOI: https://doi.org/10.3354/ame01707 Emiliania huxleyi population growth rate response to light and temperature: a synthesis Samuel R. Fielding* School of Environmental Sciences, 4 Brownlow Street, University of Liverpool, Liverpool L69 3GP, UK *Corresponding author: s.r.fielding@outlook.com ABSTRACT: The relationship between the maximum specific growth rate (μ, d-1) of the coccolithophore Emiliania huxleyi and photon flux density (PFD, µmol photons m-2 s-1) was quantified using a combination of quantile regression and culture experiment data from the literature (n = 1387). This relationship, used in ecosystem models incorporating E. huxleyi or coccolithophores as a functional group, is often assumed to follow a Monod function although values for the model parameters vary greatly. In this analysis, a Monod function was compared with other models to determine the model which best fit E. huxleyi growth rate data. Analysis showed that a Monod model of μ = 1.858[PFD/(23.91 + PFD)] best described E. huxleyi maximum growth rate as a function of PFD. In addition, an expression combining the Monod function (this study) and the power function relating growth rate to temperature (Fielding 2013; Limnol Oceanogr 58:663–666) was calculated: when both temperature (T, °C) and PFD are known, the resulting expression μ = (0.199 × T0.716) × [PFD/(14.2 + PFD)] predicts maximum E. huxleyi specific growth rate. Current literature models either overestimate or underestimate maximum growth rate by up to 3-fold over a wide range of PFDs. The use of the Monod function and the combined expression presented here is therefore recommended for future models incorporating the growth rate of E. huxleyi when either light or both temperature and light are known. KEY WORDS: Coccolithophore · Photon flux density · PFD · Temperature · Monod function · Quantile regression · Calcium carbonate · Literature review Full text in pdf format Supplementary material PreviousNextCite this article as: Fielding SR (2014) Emiliania huxleyi population growth rate response to light and temperature: a synthesis. Aquat Microb Ecol 73:163-170. https://doi.org/10.3354/ame01707 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 73, No. 2. Online publication date: October 02, 2014 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2014 Inter-Research.

EFFECTS OF DIFFERENT POTENTIAL FOOD SOURCES ON UPPER-BATHYAL BENTHIC FORAMINIFERA: AN EXPERIMENT WITH PROPAGULES

Research Article| October 01, 2014 EFFECTS OF DIFFERENT POTENTIAL FOOD SOURCES ON UPPER-BATHYAL BENTHIC FORAMINIFERA: AN EXPERIMENT WITH PROPAGULES Christopher J. Duffield; Christopher J. Duffield 4 1Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, 0316 Oslo, Norway 4Correspondence author. E-mail: c.j.duffield@geo.uio.no Search for other works by this author on: GSW Google Scholar Bente Edvardsen; Bente Edvardsen 2Department of Biosciences, University of Oslo, P.O. Box 1066, Blindern, N-0316 Oslo, Norway Search for other works by this author on: GSW Google Scholar Wenche Eikrem; Wenche Eikrem 2Department of Biosciences, University of Oslo, P.O. Box 1066, Blindern, N-0316 Oslo, Norway3Norwegian Institute for Water Research, Gaustadalléen 21, 0349 Oslo, Norway Search for other works by this author on: GSW Google Scholar Elisabeth Alve Elisabeth Alve 1Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, 0316 Oslo, Norway Search for other works by this author on: GSW Google Scholar Journal of Foraminiferal Research (2014) 44 (4): 416–433. https://doi.org/10.2113/gsjfr.44.4.416 Article history received: 30 Aug 2013 accepted: 04 Apr 2014 first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Christopher J. Duffield, Bente Edvardsen, Wenche Eikrem, Elisabeth Alve; EFFECTS OF DIFFERENT POTENTIAL FOOD SOURCES ON UPPER-BATHYAL BENTHIC FORAMINIFERA: AN EXPERIMENT WITH PROPAGULES. Journal of Foraminiferal Research 2014;; 44 (4): 416–433. doi: https://doi.org/10.2113/gsjfr.44.4.416 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search Abstract A propagule experiment was designed to investigate the effects of different food types and varying sediment depths on the survival and growth of upper-bathyal benthic foraminifera, collected from surface-sediment cores in Oslofjord, Norway. Sediment that passed through a 53-μm sieve was used in the experiment. Any foraminifera >63 μm at the end of the experiment had therefore grown, indicating at least tolerable living conditions. The experiment was arranged into four sub-experiments to test foraminiferal responses to a lack of food input, algal medium, sediment depth (1- vs. 2-cm depth), and different food types. Potential food sources included monospecific algal cultures (the green alga Dunaliella tertiolecta, the haptophyte Emiliania huxleyi, and the diatoms Chaetoceros sp. and cf. Navicula), as well as phytoplankton and zooplankton from net hauls collected at the same sampling site. After six weeks all foraminiferal assemblages showed an increase in abundance, even those which were not fed. This suggests that most species (e.g., Textularia earlandi, Bathysiphon flexilis) were feeding on microbes or detritus already in the sediment. However, the addition of certain phytodetritus increased the abundance, suggesting that some species (e.g., Epistominella vitrea) are dependent on the input of this particular fresh phytodetritus. Conversely, certain types of detritus (E. huxleyi and zooplankton) appear detrimental to most species, except Elphidium excavatum which appeared resistant to the treatments inimicable to other species. Leptohalysis catella was the only species observed to respond positively to net hauls dominated by dinoflagellates. For some species (e.g., Stainforthia fusiformis, Nonionella iridea) the availability of a greater sediment depth stimulates growth more than the input of organic matter. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Genotyping an <i>Emiliania huxleyi</i> (prymnesiophyceae) bloom event in the North Sea reveals evidence of asexual reproduction

Abstract. Due to the unprecedented rate at which our climate is changing, the ultimate consequence for many species is likely to be either extinction or migration to an alternate habitat. Certain species might, however, evolve at a rate that could make them resilient to the effects of a rapidly changing environment. This scenario is most likely to apply to species that have large population sizes and rapid generation times, such that the genetic variation required for adaptive evolution can be readily supplied. Emiliania huxleyi (Lohm.) Hay and Mohler (Prymnesiophyceae) is likely to be such a species, as it is the most conspicuous extant calcareous phytoplankton species in our oceans with growth rates of 1 day−1. Here we report on a validated set of microsatellites, in conjunction with the coccolithophore morphology motif genetic marker, to genotype 93 clonal isolates collected from across the world. Of these, 52 came from a single bloom event in the North Sea collected on the D366 United Kingdom Ocean Acidification cruise in June–July 2011. There were 26 multilocus genotypes (MLGs) encountered only once in the North Sea bloom and 8 MLGs encountered twice or up to six times. Each of these repeated MLGs exhibited Psex values of less than 0.05, indicating each repeated MLG was the product of asexual reproduction and not separate meiotic events. In addition, we show that the two most polymorphic microsatellite loci, EHMS37 and P01E05, are reporting on regions likely undergoing rapid genetic drift during asexual reproduction. Despite the small sample size, there were many more repeated genotypes than previously reported for other bloom-forming phytoplankton species, including a previously genotyped E. huxleyi bloom event. This study challenges the current assumption that sexual reproduction predominates during bloom events. Whilst genetic diversity is high amongst extant populations of E. huxleyi, the root cause for this diversity and ultimate fate of these populations still requires further examination. Nonetheless, we show that certain CMM genotypes are found everywhere, while others appear to have a regional bias.

Biomineralization: Long-Term Effectiveness of Polysaccharides on the Growth and Dissolution of Calcite

Our results demonstrate that in addition to being used for controlling morphology during calcite growth, polysaccharide (PS) that has been designed for biomineralization is also extremely robust, influencing calcite reactions even after millions of years. We investigated calcite (CaCO3) behavior in solutions with very small concentrations of PS that was produced ∼70 Ma ago by coccolithophorids. We used atomic force microscopy (AFM) and the constant composition method to monitor calcite growth in the presence of this ancient PS. The ancient PS is still very active and has a high affinity for calcite step edges. Adsorption, even at extremely low concentrations (0.5 μg/mL), results in decreased growth rate and dramatic morphology changes during growth and dissolution. The experimental results are complemented with surface complexation modeling for adsorption of components of polysaccharide from a modern coccolithophorid, Emiliania huxleyi. We generated surface complexation constants for the branch components: malonate: 14.25 ± 0.17, succinate: 11.91 ± 0.06, tricarballylate: 14.86 ± 0.04, and citrate: 15.25 ± 0.04. The implication is that complex PS could hold promise for smart material engineering and for preventing scaling.

Phenotypic diversity of diploid and haploid Emiliania huxleyi cells and of cells in different growth phases revealed by comparative metabolomics

In phytoplankton a high species diversity of microalgae co-exists at a given time. But diversity is not only reflected by the species composition. Within these species different life phases as well as different metabolic states can cause additional diversity. One important example is the coccolithophore Emiliania huxleyi. Diploid cells play an important role in marine ecosystems since they can form massively abundant algal blooms but in addition the less abundant haploid life phase of E. huxleyi occurs in lower quantities. Both life phases may fulfill different functions in the plankton. We hypothesize that in addition to the functional diversity caused by this life phase transition the growth stage of cells can also influence the metabolic composition and thus the ecological impact of E. huxleyi. Here we introduce a metabolomic survey in dependence of life phases as well as different growth phases to reveal such changes. The comparative metabolomic approach is based on the extraction of intracellular metabolites from intact microalgae, derivatization and analysis by gas chromatography coupled to mass spectrometry (GC-MS). Automated data processing and statistical analysis using canonical analysis of principal coordinates (CAP) revealed unique metabolic profiles for each life phase. Concerning the correlations of metabolites to growth phases, complex patterns were observed. As for example the saccharide mannitol showed its highest concentration in the exponential phase, whereas fatty acids were correlated to stationary and sterols to declining phase. These results are indicative for specific ecological roles of these stages of E. huxleyi and are discussed in the context of previous physiological and ecological studies.

Numerical cell model investigating cellular carbon fluxes in Emiliania huxleyi

Coccolithophores play a crucial role in the marine carbon cycle and thus it is interesting to know how they will respond to climate change. After several decades of research the interplay between intracellular processes and the marine carbonate system is still not well understood. On the basis of experimental findings given in literature, a numerical cell model is developed that describes inorganic carbon fluxes between seawater and the intracellular sites of calcite precipitation and photosynthetic carbon fixation. The implemented cell model consists of four compartments, for each of which the carbonate system is resolved individually. The four compartments are connected to each other via H+, CO2, and HCO3− fluxes across the compartment-confining membranes. For CO2 accumulation around RubisCO, an energy-efficient carbon concentrating mechanism is proposed that relies on diffusive CO2 uptake. At low external CO2 concentrations and high light intensities, CO2 diffusion does not suffice to cover the carbon demand of photosynthesis and an additional uptake of external HCO3− becomes essential. The model is constrained by data of Emiliania huxleyi, the numerically most abundant coccolithophore species in the present-day ocean.

Environmental control on phytoplankton community structure in the NE Black Sea

Long-term field observation carried out in northeastern (NE) part of the Black Sea in 2005–2010, revealed strong environmental control over phytoplankton community structure, in particular the relationship between the diatoms and coccolithophores. We followed the changes of phytoplankton community structure in marine water every year from May to June. An intense bloom of coccolithophores Emiliania huxleyi was observed in 2005–2006 when the nitrogen in marine water declined and the N/P ratio dropped below the Redfield proportion. In the 2007–2008, N/P ratio increased above the Redfield stoichiometry leading to the domination of the diatoms in phytoplankton community. The predominance of E. huxleyi was observed again in 2009–2010 and again it was associated with the decrease of the N/P ratio. To confirm the observation correlation between community composition and the mineral nutrient concentrations we undertook laboratory microcosm studies with addition of various amounts of a nitrogen and phosphorus sources to marine water. It was found that decreased nitrogen level and respective lower N/P stoichiometric ratio were essential precondition for coccolithophores domination. Under increased concentration of nitrogen and phosphorus near and above the Redfield stoichiometry, always encouraged the development of diatoms. We conclude that at least in the NE-part of the Black Sea, the composition of spring and summer phytoplankton is under strict environmental control by availability of mineral nutrients.

Morphology of <i>Emiliania huxleyi</i> coccoliths on the northwestern European shelf – is there an influence of carbonate chemistry?

Abstract. Within the context of the UK Ocean Acidification project, Emiliania huxleyi (type A) coccolith morphology was examined from samples collected during cruise D366. In particular, a morphometric study of coccolith size and degree of calcification was made on scanning electron microscope images of samples from shipboard CO2 perturbation experiments and from a set of environmental samples with significant variation in calcite saturation state (Ωcalcite). One bioassay in particular (E4 from the southern North Sea) yielded unambiguous results – in this bioassay exponential growth from a low initial cell density occurred with no nutrient enrichment and coccosphere numbers increased tenfold during the experiment. The samples with elevated CO2 saw significantly reduced coccolithophore growth. However, coccolithophore morphology was not significantly affected by the changing CO2 conditions even under the highest levels of perturbation (1000 μatm CO2). Environmental samples similarly showed no correlation of coccolithophore morphology with calcite saturation state. Some variation in coccolith size and degree of calcification does occur but this seems to be predominantly due to genotypic differentiation between populations on the shelf and in the open ocean.

Hijacking of an autophagy-like process is critical for the life cycle of a DNA virus infecting oceanic algal blooms.

Marine photosynthetic microorganisms are the basis of marine food webs and are responsible for nearly 50% of the global primary production. Emiliania huxleyi forms massive oceanic blooms that are routinely terminated by large double-stranded DNA coccolithoviruses. The cellular mechanisms that govern the replication cycle of these giant viruses are largely unknown.We used diverse techniques, including fluorescence microscopy, transmission electron microscopy, cryoelectron tomography, immunolabeling and biochemical methodologies to investigate the role of autophagy in host–virus interactions.Hallmarks of autophagy are induced during the lytic phase of E. huxleyi viral infection, concomitant with up-regulation of autophagy-related genes (ATG genes). Pretreatment of the infected cells with an autophagy inhibitor causes a major reduction in the production of extracellular viral particles, without reducing viral DNA replication within the cell. The host-encoded Atg8 protein was detected within purified virions, demonstrating the pivotal role of the autophagy-like process in viral assembly and egress.We show that autophagy, which is classically considered as a defense mechanism, is essential for viral propagation and for facilitating a high burst size. This cellular mechanism may have a major impact on the fate of the viral-infected blooms, and therefore on the cycling of nutrients within the marine ecosystem.

Surface biological, chemical, and optical properties of the Patagonian Shelf coccolithophore bloom, the brightest waters of the Great Calcite Belt

We report surface observations of a mesoscale coccolithophore bloom at the shelf break of the Patagonian Shelf during December 2008, representing the densest coccolithophore population in the Southern Ocean. The bloom was most intense within the Falklands Current, northeast of the Falkland Islands. Emiliania huxleyi dominated bloom waters, with a mixed E. huxleyi and Prorocentrum sp. dinoflagellate bloom to the west and mixed assemblage of diatoms, dinoflagellates, and flagellates to the east. Optical measurements of coccolith light scattering, analytical measurements of their calcite, and microscopic counts all showed this to be an intense coccolithophore bloom. Average particulate inorganic carbon per coccolith in the bloom was low, typical of the B coccolith morphotype and in agreement with independent measurements made by scanning electron microscopy. Highest particulate inorganic carbon (measured optically and chemically) was observed when residual nitrate (defined as the difference, [NO3−1] − [Si(OH)4]) was 10–17 µmol L−1 and nitrate to phosphate ratios were close to Redfield values. Elevated particle backscattering was observed in the E. huxleyi bloom, whereas the highest particle scattering occurred in the adjoining Prorocentrum sp. bloom. Backscattering from coccolithophores represented up to 50% of the total backscattering (from organic and inorganic particles) along the main axis of the E. huxleyi bloom. Chlorophyll‐specific absorption in the coccolithophore bloom was typical of marine phytoplankton. Residual nitrate plotted vs. temperature showed that the E. huxleyi bloom was associated with waters between 5°C and 15°C, with depleted silicate. Results suggest that previous drawdown of silicate by diatoms occurred prior to the densest E. huxleyi blooms over the Patagonian Shelf. We speculate that such conditions might also be important for annual development of the broader Great Calcite Belt and other coccolithophore blooms..

Alternatives to vitamin B1 uptake revealed with discovery of riboswitches in multiple marine eukaryotic lineages.

Vitamin B1 (thiamine pyrophosphate, TPP) is essential to all life but scarce in ocean surface waters. In many bacteria and a few eukaryotic groups thiamine biosynthesis genes are controlled by metabolite-sensing mRNA-based gene regulators known as riboswitches. Using available genome sequences and transcriptomes generated from ecologically important marine phytoplankton, we identified 31 new eukaryotic riboswitches. These were found in alveolate, cryptophyte, haptophyte and rhizarian phytoplankton as well as taxa from two lineages previously known to have riboswitches (green algae and stramenopiles). The predicted secondary structures bear hallmarks of TPP-sensing riboswitches. Surprisingly, most of the identified riboswitches are affiliated with genes of unknown function, rather than characterized thiamine biosynthesis genes. Using qPCR and growth experiments involving two prasinophyte algae, we show that expression of these genes increases significantly under vitamin B1-deplete conditions relative to controls. Pathway analyses show that several algae harboring the uncharacterized genes lack one or more enzymes in the known TPP biosynthesis pathway. We demonstrate that one such alga, the major primary producer Emiliania huxleyi, grows on 4-amino-5-hydroxymethyl-2-methylpyrimidine (a thiamine precursor moiety) alone, although long thought dependent on exogenous sources of thiamine. Thus, overall, we have identified riboswitches in major eukaryotic lineages not known to undergo this form of gene regulation. In these phytoplankton groups, riboswitches are often affiliated with widespread thiamine-responsive genes with as yet uncertain roles in TPP pathways. Further, taxa with ‘incomplete' TPP biosynthesis pathways do not necessarily require exogenous vitamin B1, making vitamin control of phytoplankton blooms more complex than the current paradigm suggests.

Effects of growth stages, respiration, and microbial degradation of phytoplankton on cellular lipids and their compound-specific stable carbon isotopic compositions

A series of laboratory experiments were conducted to examine effects of biochemical processes on phytoplankton lipids and their stable carbon isotopic compositions. Thalassiosira weissflogii and Emiliania huxleyi were axenically cultivated in batch cultures through exponential growth (phase I) and stationary period (phase II), followed by dark respiration (phase III) and subsequent microbial degradation (phase IV). The results indicated that the bulk parameters, lipid contents and associated isotopic compositions of two phytoplankton species varied differently during different cell growth stages, cell respiration and microbial degradation processes. T. weissflogii continuously produced neutral lipids and fatty acids at similar rates between phase I and phase II. By contrast, E. huxleyi produced neutral lipids at faster rates in phase II than in phase I although the production rates of fatty acids were still similar between the two phases. The lipid isotopic compositions of these two phytoplankton species varied in a similar pattern through cell growth: remarkably positive shift in phase I but relatively small negative shift or little change in phase II. During cell respiration (phase III), two phytoplanktons lost their lipids by varying percentages but the isotopic compositions of all compounds remained relatively constant. With degradation of lipids in phase IV, their isotopic compositions varied in three different ways: positive shift for most fatty acids; little change for sterols and alkenones; and a negative shift for 20:5 fatty acid of T. weissflogii. This experimental study implies: (1) isotopic compositions of phytoplankton lipids are heterogeneously generated through different cell growth phases, likely dependent on cell physiological states, medium conditions, and relative proportions of intracellular components; and (2) microbial degradation plays a more important role in altering isotopic compositions of lipid compounds than cell respiration, probably related to different labilities of lipids between different cellular components.

Isotopic fractionation of carbon in the coccolithophorid Emiliania huxleyi

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 508:53-66 (2014) - DOI: https://doi.org/10.3354/meps10840 Isotopic fractionation of carbon in the coccolithophorid Emiliania huxleyi Dan Tchernov1,*, David F. Gruber2, Andrew Irwin3 1Marine Biology Department, The Leon H. Charney School of Marine Sciences, University of Haifa, Mount Carmel, Haifa 31905, Israel 2Department of Natural Sciences, Baruch College, City University of New York and Sackler Institute for Comparative Genomics, American Museum of Natural History, New York, NY, USA3Department of Mathematics and Computer Science, Mount Allison University, Sackville, New Brunswick, Canada *Corresponding author: dtchernov@univ.haifa.ac.il ABSTRACT: Relating atmospheric CO2 to β13C of calcifying phytoplankton is often used as a proxy to reconstruct paleo-CO2. Therefore, a firm undertanding of how living cells fractionate carbon under different environmental conditions (known as vital effects) is necessary when interpreting δ13C values. In this study, we measured the isotopic fractionation of carbon in organic matter (ε p) in the globally distributed, bloom-forming coccolithophorid Emiliania huxleyi grown in continuous culture under nutrient-replete conditions with growth rate limited by light or temperature. At a constant temperature of 18°C, growth followed a hyperbolic function of irradiance. At low irradiance levels, changes in ε p were highly correlated with growth rate. However, as growth became light-saturated, ε p declined with increasing light intensities. When temperature was increased from 7 to 18°C at a constant photon flux density, equilibrium partial pressure CO2 concentrations ([pCO2]) decreased from 17 to 13 µM, and ε p values declined from 25 to 19‰. As temperature was increased further to 26°C, [pCO2] declined to 10 µM and ε p increased to 25‰. This non-linear pattern in isotopic fractionation is consistent with the induction of a carbon-concentrating mechanism at low [pCO2] that replenishes the internal inorganic carbon pool with isotopically lighter carbon. In this study, we present an empirical model that predicts this non-linear behavior, and we validate this model with experimental data. These results suggest extreme variability in the isotopic fractionation of carbon in the bulk organic pool in E. huxleyi that precludes the reconstruction of pCO2 from isotopic measurements without a priori knowledge of temperature. KEY WORDS: Emiliania huxleyi · Calcifying phytoplankton · Isotopic fractionation of carbon · Vital effects · Paleo-CO2 reconstruction · Temperature · Carbon-concentrating mechanism Full text in pdf format PreviousNextCite this article as: Tchernov D, Gruber DF, Irwin A (2014) Isotopic fractionation of carbon in the coccolithophorid Emiliania huxleyi . Mar Ecol Prog Ser 508:53-66. https://doi.org/10.3354/meps10840 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 508. Online publication date: August 04, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Between‐ and within‐population variations in thermal reaction norms of the coccolithophore Emiliania huxleyi

Thermal reaction norms for growth rates of six Emiliania huxleyi isolates originating from the central Atlantic (Azores, Portugal) and five isolates from the coastal North Atlantic (Bergen, Norway) were assessed. We used the template mode of variation model to decompose variations in growth rates into modes of biological interest: vertical shift, horizontal shift, and generalist—specialist variation. In line with the actual habitat conditions, isolates from Bergen (Bergen population) grew well at lower temperatures, and isolates from the Azores (Azores population) performed better at higher temperatures. The optimum growth temperature of the Azores population was significantly higher than that of the Bergen population. Neutral genetic differentiation was found between populations by microsatellite analysis. These findings indicate that E. huxleyi populations are adapted to local temperature regimes. Next to between‐population variation, we also found variation within populations. Genotype‐by‐environment interactions resulted in the most pronounced phenotypic differences when isolates were exposed to temperatures outside the range they naturally encounter. Variation in thermal reaction norms between and within populations emphasizes the importance of using more than one isolate when studying the consequences of global change on marine phytoplankton. Phenotypic plasticity and standing genetic variation will be important in determining the potential of natural E. huxleyi populations to cope with global climate change.

How many Coccolithovirus genotypes does it take to terminate an Emiliania huxleyi bloom?

Giant viruses are known to be significant mortality agents of phytoplankton, often being implicated in the terminations of large Emiliania huxleyi blooms. We have previously shown the high temporal variability of E. huxleyi-infecting coccolithoviruses (EhVs) within a Norwegian fjord mesocosm. In the current study we investigated EhV dynamics within a naturally-occurring E. huxleyi bloom in the Western English Channel. Using denaturing gradient gel electrophoresis and marker gene sequencing, we uncovered a spatially highly dynamic Coccolithovirus population that was associated with a genetically stable E. huxleyi population as revealed by the major capsid protein gene (mcp) and coccolith morphology motif (CMM), respectively. Coccolithoviruses within the bloom were found to be variable with depth and unique virus populations were detected at different stations sampled indicating a complex network of EhV-host infections. This ultimately will have significant implications to the internal structure and longevity of ecologically important E. huxleyi blooms.