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  • 1
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    Pan genome of the phytoplankton Emiliania underpins its global distribution (2013)
    Nature Publishing Group
    In:  EPIC3Nature, Nature Publishing Group, ISSN: 0028-0836
    Details
    Publication Date: 2019-03-08
    Description: Coccolithophores have influenced the global climate for over 200 million years1. These marine phytoplankton can account for 20 per cent of total carbon fixation in some systems2. They form blooms that can occupy hundreds of thousands of square kilometres and are distinguished by their elegantly sculpted calcium carbonate exoskeletons (coccoliths), rendering themvisible fromspace3.Although coccolithophores export carbon in the form of organic matter and calcite to the sea floor, they also release CO2 in the calcification process. Hence, they have a complex influence on the carbon cycle, driving either CO2 production or uptake, sequestration and export to the deep ocean4. Here we report the first haptophyte reference genome, from the coccolithophore Emiliania huxleyi strain CCMP1516, and sequences from 13 additional isolates. Our analyses reveal a pan genome (core genes plus genes distributed variably between strains) probably supported by an atypical complement of repetitive sequence in the genome. Comparisons across strains demonstrate thatE. huxleyi, which has long been considered a single species, harbours extensive genome variability reflected in different metabolic repertoires. Genome variability within this species complex seems to underpin its capacity both to thrive in habitats ranging from the equator to the subarctic and to form large-scale episodic blooms under a wide variety of environmental conditions.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
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    An aerobic eukaryotic parasite with functional mitochondria that likely lacks a mitochondrial genome (2019)
    American Association for the Advancement of Science
    In:  EPIC3Science Advances, American Association for the Advancement of Science, 5(4), ISSN: 2375-2548
    Details
    Publication Date: 2020-02-12
    Description: Dinoflagellates are microbial eukaryotes that have exceptionally large nuclear genomes; however, their organelle genomes are small and fragmented and contain fewer genes than those of other eukaryotes. The genus Amoebophrya (Syndiniales) comprises endoparasites with high genetic diversity that can infect other dinoflagellates, such as those forming harmful algal blooms (e.g., Alexandrium). We sequenced the genome (~100 Mb) of Amoebophrya ceratii to investigate the early evolution of genomic characters in dinoflagellates. The A. ceratii genome encodes almost all essential biosynthetic pathways for self-sustaining cellular metabolism, suggesting a limited dependency on its host. Although dinoflagellates are thought to have descended from a photosynthetic ancestor, A. ceratii appears to have completely lost its plastid and nearly all genes of plastid origin. Functional mitochondria persist in all life stages of A. ceratii, but we found no evidence for the presence of a mitochondrial genome. Instead, all mitochondrial proteins appear to be lost or encoded in the A. ceratii nucleus.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 3
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    Adaptive divergence across Southern Ocean gradients in the pelagic diatomFragilariopsis kerguelensis. (2020)
    WILEY-BLACKWELL PUBLISHING
    In:  EPIC3Molecular Ecology, WILEY-BLACKWELL PUBLISHING, 24, pp. 4754-4756, ISSN: 0962-1083
    Details
    Publication Date: 2021-02-16
    Description: The Southern Ocean is characterized by longitudinal water circulations crossed by strong latitudinal gradients. How this oceanographic background shapes planktonic populations is largely unknown, despite the significance of this region for global biogeochemical cycles. Here, we show, based on genomic, morphometric, ecophysiological and mating compatibility data, an example of ecotypic differentiation and speciation within an endemic pelagic inhabitant, the diatom Fragilariopsis kerguelensis. We discovered three genotypic variants, one present throughout the latitudinal transect sampled, the others restricted to the north and south, respectively. The latter two showed reciprocal monophyly across all three genomes and significant ecophysiological differences consistent with local adaptation, but produced viable offspring in laboratory crosses. The third group was also reproductively isolated from the latter two. We hypothesize that this pattern originated by an adaptive expansion accompanied by ecotypic divergence, followed by sympatric speciation.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    Biodiversity assessment and transcriptomic analyzes of eukaryotic sea ice diatoms of the central Arctic Ocean (2015)
    In:  EPIC36th European Phycological Congress
    Details
    Publication Date: 2017-02-16
    Description: Sea ice is a large environment controlled by a number of abiotic factors (i.e. low temperatures and high salinities). Despite these harsh conditions, it is inhabited by a diverse community and significantly contributing to primary production in ice-covered regions. While this biodiversity has been investigated in the past by classical methods, little is known about its functional biodiversity, i.e. which species are actively contributing with which functions to the community. By sequencing 18S rRNA and rDNA amplicons, we were able to compare the “total” biodiversity (rDNA-based) with the “active” biodiversity (rRNA-based) and found an over-representation of certain groups (i.e. Bacillariophyceae and Ciliophora) in the active part of the community. Furthermore, we were able to isolate an abundant naviculoid sea ice diatom member (CCMP2297) of the Arctic sea ice community and conducted temperature stress experiments (10 °C, 5 °C, -2 °C, -5 °C) and analyzed not only physiological responses to high and cold temperature stress, but also the molecular responses to thermal stress by sequencing the transcriptome. We found that based on physiological parameters this diatom has a broad thermal range (5 °C to -5 °C) but significantly changes its gene expression pattern at higher temperatures.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 5
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    Transcriptomic profiling of Alexandrium fundyense during physical interaction with or exposure to chemical signals from the parasite Amoebophrya (2016)
    In:  EPIC3Molecular Ecology, 25(6), pp. 1294-1307
    Details
    Publication Date: 2019-03-08
    Description: Toxic microalgae have their own pathogens, and understanding the way in which these microalgae respond to antagonistic attacks may provide information about their capacity to persist during harmful algal bloom events. Here, we compared the effects of the physical presence of the parasite Amoebophrya sp. and exposure to waterborne cues from cultures infected with this parasite, on gene expression by the toxic dinoflagellates, Alexandrium fundyense. Compared with control samples, a total of 14 882 Alexandrium genes were differentially expressed over the whole-parasite infection cycle at three different time points (0, 6 and 96 h). RNA sequencing analyses indicated that exposure to the parasite and parasitic waterborne cues produced significant changes in the expression levels of Alexandrium genes associated with specific metabolic pathways. The observed upregulation of genes associated with glycolysis, the tricarboxylic acid cycle, fatty acid β-oxidation, oxidative phosphorylation and photosynthesis suggests that parasite infection increases the energy demand of the host. The observed upregulation of genes correlated with signal transduction indicates that Alexandrium could be sensitized by parasite attacks. This response might prime the defence of the host, as indicated by the increased expression of several genes associated with defence and stress. Our findings provide a molecular overview of the response of a dinoflagellate to parasite infection.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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  • 6
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    Polyketide synthesis genes associated with toxin production in two species of Gambierdiscus (Dinophyceae) (2015)
    BIOMED CENTRAL LTD
    In:  EPIC3BMC Genomics, BIOMED CENTRAL LTD, 16, pp. 410, ISSN: 1471-2164
    Details
    Publication Date: 2015-07-06
    Description: Background: Marine microbial protists, in particular, dinoflagellates, produce polyketide toxins with ecosystem-wide and human health impacts. Species of Gambierdiscus produce the polyether ladder compounds ciguatoxins and maitotoxins, which can lead to ciguatera fish poisoning, a serious human illness associated with reef fish consumption. Genes associated with the biosynthesis of polyether ladder compounds are yet to be elucidated, however, stable isotope feeding studies of such compounds consistently support their polyketide origin indicating that polyketide synthases are involved in their biosynthesis. Results: Here, we report the toxicity, genome size, gene content and transcriptome of Gambierdiscus australes and G. belizeanus. G. australes produced maitotoxin-1 and maitotoxin-3, while G. belizeanus produced maitotoxin-3, for which cell extracts were toxic to mice by IP injection (LD50 = 3.8 mg kg(-1)). The gene catalogues comprised 83,353 and 84,870 unique contigs, with genome sizes of 32.5 +/- 3.7 Gbp and 35 +/- 0.88 Gbp, respectively, and are amongst the most comprehensive yet reported from a dinoflagellate. We found three hundred and six genes involved in polyketide biosynthesis, including one hundred and ninty-two ketoacyl synthase transcripts, which formed five unique phylogenetic clusters. Conclusions: Two clusters were unique to these maitotoxin-producing dinoflagellate species, suggesting that they may be associated with maitotoxin biosynthesis. This work represents a significant step forward in our understanding of the genetic basis of polyketide production in dinoflagellates, in particular, species responsible for ciguatera fish poisoning.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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