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Keynote presentations

  1. Chris Bowler
  2. Daniel Conley
  3. Indrani Karunasagar
  4. Nina Lundholm
  5. Tatiana Rynearson
  6. Wim Vyverman

Chris Bowler,
École Normale Supérieure, France

Ancient DNA

Daniel Conley,
Dept Geology, Lund Universit, Sweden

Perspectives on the evolution of diatoms

Although molecular clocks suggest that diatoms evolved over 200 Ma ago, this result has been largely ignored because of the lack of diatoms in the geologic fossil record with most studies therefore focused on diversification during the mid-Cenozoic period 30 Ma ago where abundant diatom fossils are found. Much of the older fossil evidence has likely been destroyed by dissolution during diagenesis, subducted or is concealed deep within the Earth. My new ERC project, DEVOCEAN, will provide evidence on diatom evolution and speciation in the geological record by examining formations representing locations in which diatoms are likely to have accumulated in ocean sediments. We will generate robust estimates of the timing and magnitude of dissolved Si drawdown following the origin of diatoms using the isotopic silicon composition of fossil sponge spicules and radiolarians. The project will also provide fundamental new insights into the timing of dissolved Si drawdown and other key events, which reorganized the distribution of carbon and nutrients in seawater, changing energy flows and productivity in the biological communities of the ancient oceans.

Indrani Karunasagar,
Nitte University Centre for Science Education and Research, India

Climate change, oceans, blooms, toxins, and outbreaks : Impact on aquaculture and human health

Nina Lundholm,
Natural History Museum of Denmark, University of Copenhagen, Denmark

Induction of domoic acid production - grazers and diatom species

In costal ecosystems copepods co-exist with toxin-producing phytoplankton. Grazers can induce toxin (domoic acid) production in diatoms, but this has only been studied in two species of Pseudo-nitzschia and induced by Calanus copepods. We explored induction by different grazers and found that all herbivorous copepods induced toxin production, whereas carnivorous copepods did not. The induced response is thus only elicited by copepods that pose a real threat to the responding cells, which supports that the induced toxin production in diatoms evolved as an inducible defense. Our results suggest that copepodamides, polar lipids, are the chemical cues responsible for triggering the DA production. Long-term grazing experiments showed higher mortality rates of grazers fed toxic diatoms, supporting the idea that DA production is an induced defense mechanism.
Among the diatoms exposed to copepods, only two of six species of Pseudo-nitzschia responded by producing DA, indicating that different diatom species have different strategies for coping with grazing pressure. Ten days after removal of the copepods, the cellular DA was reduced to 22-35% and further extrapolation suggests that it take the diatom cells up to 6 weeks to reach initial DA levels.

Tatiana Rynearson,
University of Rhode Island, USA

Not all Skeletonema are created equal. Thermal traits, genetic diversity, and bloom dynamics in Narragansett Bay, RI.

Tatiana Rynearson and Stephanie Anderson, University of Rhode Island

The ecologically important diatom genus, Skeletonema, can form large blooms and is distributed globally. Because most species in the genus are morphologically cryptic, there is limited understanding of their spatial and temporal distribution as well as the physiological underpinnings responsible for their ecological success. To examine how diversity and physiology shape Skeletonema ecology, we are employing high-throughput sequencing and physiological trait assays of single cell isolates, in combination with long-term time series data. Our work has focused on Narragansett Bay, RI, USA, where Skeletonema spp. comprise 49% of the >10 micron phytoplankton and up to 99% during blooms. Our results suggest a diverse community of Skeletonema inhabits the bay. A modeling effort to combine physiological trait assays with high throughput sequencing revealed seasonal patterns of abundance are driven primarily by thermal traits. With projected increases in sea surface temperature, we predict a shift in Skeletonema bloom dynamics, which may impact energy flux through coastal food webs.

Wim Vyverman,
Ghent University, Laboratory of Protistology and Aquatic Ecology, Belgium

Sexual reproduction and speciation in diatoms 


  1. Akira Kuwata
  2. Andrew Alverson
  3. Angela Wulff
  4. Anushree Sanyal
  5. Bengt Karlson
  6. Carl-Joar Karlsson
  7. Conny Sjöqvist
  8. Cornelia Spetea Wiklund
  9. Elinor Andrén
  10. Emma Johansson
  11. Erik Selander
  12. Giannina Hattich
  13. Ingrid Sassenhagen
  14. Jonathan Havenhand
  15. Josefin Sefbom
  16. Luca Zoccarato
  17. Maria Kahlert
  18. Marianne Ellegaard
  19. Mariella Ferrante
  20. Marina Montresor
  21. Mats Töpel
  22. Olga Kourtchenko
  23. Pierre De Wit
  24. Sandra Lage
  25. Valeria Villanova

Akira Kuwata,
Tohoku National Fisheries Research Institute, FRA, Japan

Biology of a picoeukaryotic phytoplankton, Parmales(Bolidophyceae), a sister group of diatoms.

Parmales (Bolidophyceae) is a group of pico-eukaryotic marine phytoplankton with both silicified and naked flagellated types, which distribute widely in the world’s oceans, from polar to subtropical regions. Recent success of isolation of the silicified types of Parmales from the Oyashio water in the Western Subarctic Pacific and characterizing of these isolated strains revealed that Parmales belong to Heterokonta and share a common ancestor with diatoms. I would like to present current information of this group obtained by our phyogenetical, physiological, ecological and genomic studies, and to discuss similarities and differences between Parmales and diatoms from ecological, and evolutionary view.

Andrew Alverson,
University of Arkansas, USA

Population genomics of Skeletonema marinoi across the Baltic Sea salinity gradient.

Salinity is a principal barrier to the distribution of microbes, including diatoms, where adaptation to low-salinity habitats has occurred repeatedly and is associated with increased rates of both speciation and extinction. Skeletonema marinoi is distributed in coastal marine habitats worldwide, and it also occurs across the length of the Baltic Sea, which is famous for its steep salinity cline. Using a novel sequence capture system, we sequenced 400 individuals of S. marinoi from 10 populations across the Baltic Sea. We are using these data to characterize population structure, patterns of gene flow, and the genomic basis of adaptation to low salinity.

Angela Wulff
Dept Biological and Environmental Sciences, University of Gothenburg, Sweden

Diatom frustules - Useful miracles designed by evolution.

The diatom frustule is incorporated by silica and ornamented with pores down to nano-size - each species with a unique pattern. Protection from ultraviolet radiation (UVR) may be one reason for the evolution of frustules. Experimental evidence for harmful UVR effects is found for many species, but it is also clear that diatoms can cope with high UVR intensities. We observed high UVR tolerance in pennate diatoms despite that they, in contrast to centrics, contain no or only very small amounts of UVR-absorbing compounds. We suggest that the redistribution of UVR, is an important evolutionary cause of the presence and evolution of frustules, by decreasing the UVR-induced degradation of DNA inside the cells.

The ability of the frustules to protect from UVR can be utilized also to protect humans and sensitive materials from harmful wavelengths. Furthermore, the intrinsic structure of the frustules can enhance the efficiency of solar panels by improved light absorptions and redistribution of UVR. In addition, the precise nano-sized structure of the frustules is designed for uptake and release of e.g. gases and chemicals. This feature is being explored in several applications including skin care products, batteries, sensors and drug delivery.

Anushree Sanyal
Swedish University of Agricultural Sciences, Sweden

Not dead yet: Diatom resting spores can survive in nature for several millennia.

We show for the first time the revival, viability and germination rate of sediment deposited resting spores of the diatom Chaetoceros from three ages (recent: 0-80 years; ancient: 1000~1300 (Medieval Climate Anomaly (MCA)) and ~6000-7200 (Holocene Thermal Maximum (HTM)) calendar year before present (BP). We show that ~7200 calendar year BP old Chaetoceros resting spores are still viable. The time taken to germinate is three hours to 2-3 days in both recent and ancient spores but the germination rate (%) of the spores decreased with increasing age. The germination rate of the recent spores were ~50% while that of the MCA and HTM ages were ~40% and ~19%, respectively. The species was identified as Chaetoceros muelleri based on the morphology of the germinated cell. Sanger sequences of nuclear and chloroplast markers were generated.

Studies of revived resting spores of marine diatoms will serve as excellent proxies of environmental change in marine environments and enable us to reconstruct diatom evolutionary history in relation to environmental changes. Comparison of resurrected populations obtained from these natural archives of diatoms can provide predictive models to forecast evolutionary responses of populations to environmental perturbations from natural and anthropogenic stressors, including climate change over longer timescales.

Bengt Karlson,
SMHI, Oceanographic Research, Sweden

Authors: Bengt Karlson, Lars Arneborg, Michael Brosnahan, Allan Cembella, Wenche Eikrem, Sten-Åke Wängberg and Anna Godhe

Algal blooms dynamics and phytoplankton diversity investigated using novel methods.

Algal blooms often have a time scale from days to weeks. To investigate the bloom dynamics high frequency sampling is needed. An automated in situ imaging flow cytometer, the Imaging FlowCytobot, was used to investigate phytoplankton composition and abundance near a mussel farm in Tångesund, on the Swedish Skagerrak coast. This was combined with metabarcoding of 18S rDNA and traditional water sampling and microscopy. Also, the physical oceanography was investigated. Short term dynamics of selected harmful algae will be presented.

Carl-Joar Karlsson,
Department of Mathematical Sciences, GU/Chalmers, Sweden

This presentation gives an overview of a project in mathematical ecology called "Game theoretic explanation of intra-specific diversity among replicating microbes". We will study the evolution of behavior in our model, and therefore, I am seeking collaborators that can provide expertise knowledge and experimental tests of our predictions.

Conny Sjöqvist,
Åbo Akademi University, Finland

In the face of ongoing anthropogenic Global Change, the key planktonic realm is subjected to new environmental conditions, inevitably forcing species to adaptive evolution or local extinction. Given a likely scenario, can we predict the performance and eco-evolutionary responses of diverse autotrophic organisms responsible of fundamental processes in the marine ecosystem? A potentially advisable approach to the question is to capitalize on the implicit ecological knowledge-potential of different types of existing data, or data we are technically capable of producing today. The aim of this research project is to combine metagenome, experimental and historic monitoring data to predict the effects of global climate change on primary producers in the ocean. The project combines 1) metagenome population genomics, 2) transcriptome profiling of pre-Anthropocene resurrected resting cells and 3) species distribution modelling of a key phytoplankton species, Skeletonema marinoi, across natural environmental gradients in a “Darwinian laboratory”, the Baltic Sea-North Sea transition. The project aims to advance methodological norms within the field of molecular ecology focused on unicellular eukaryotes. Altogether, this will bolster our ability to understand anthropogenically induced impacts on marine ecosystems, and diversify the toolbox used in studies focused on phytoplankton ecology.

Cornelia Spetea Wiklund,
Dept. Biological Environmental Sciences, University of Gothenburg, Sweden

Renewable biomass from marine microalgae

Cornelia Spetea Wiklund, Otilia Cheregi and Valeria Villanova

Society faces major challenges in the production of sufficient amounts of biomass for energy and material production. Biomass from microalgae that are rich in oil has great potential as a complement to biomass from forests and agriculture. The success of microalgae as feedstock depends on achieving high yield with minimum energy input. In collaboration with Anna Godhe, we have initiated a few years ago a new project aimed to identify marine microalgal strains (mainly Skeletonema marinoi), that are productive and can cope with the dynamic climate of the Swedish west coast. In a rotation model, different strains would be cultivated during three growth seasons. Together with researchers at RISE, we want to further develop a system shown to be energy-efficient, for outdoor cultivation of marine microalgae. This project is funded by the Swedish Energy Agency and Carl Tryggers Foundation. A related Marie Curie project in collaboration with Anna Godhe aims to develop mixotrophic cultivation to further increase productivity for selected strains of Skeletonema marinoi from the Swedish west coast. We will present the ideas behind these projects, current status and future plans.

Elinor Andrén,
Natural Sciences, Technology and Environmental Studies, Södertörn University, Sweden

Paleoecological trends and synchronicity between the open and coastal Baltic Proper

Paleoecological investigations using sediment records are needed to provide data on the range of natural variation before ecosystems were impacted by humans, as well as information on the speed and direction of change. It has been suggested that changes in agricultural practice in the Baltic Sea drainage basin as early as medieval times, some 1000 years ago, caused hypoxia in the bottom waters of the open Baltic Sea. In this study we investigate millennial paleoecological trends in an off-shore sediment stratigraphy from the western Gotland Basin and compare recorded changes with several sites in the North-western Baltic Proper coastal zone (Stockholm archipelago and Bråviken). The aim is to use diatom analysis on sediment stratigraphies to trace and date environmental change and test if changes in the open Baltic Sea occur synchronous with changes in the coastal zone.
Our result show that there are significant differences between the recorded diatom composition in the two setting. No medieval impact can be recorded in the coastal zone and the changes recorded in the open Baltic Proper must be attributed to climate. The onset of eutrophication dates to about 1800-1900 CE in the coastal zone and 1950 in the open Baltic Proper.

Emma Johansson,
Dept Biology, Lund University, Sweden

High diversity of microcystin chemotypes within a natural community of the fresh-water cyanobacteria Microcystis botrys.

The fresh-water cyanobacteria Microcystis botrys is known to produce microcystins, which are non-ribosomal peptides with toxic effects on e.g. vertebrates. More than 240 structural microcystin variants have been described, but their function remain largely unknown, and not all strains within a population produce microcystins. We monitored the seasonal variation in microcystin production in a natural Microcystis botrys population, sampled in Lake Vomb (Scania) during the summer of 2014. Our aim was to identify the specific microcystin congeners present in the population, and explore the chemotype diversity among the M. botrys strains within the particular ecosystem. The results showed that there were considerable variation in microcystin chemotypes within the sampled population, both in terms of what microcystin variants were produced, as well as in what combinations. Furthermore, toxigenic and non-toxigenic M. botrys co-existed in Lake Vomb throughout the summer season, and microcystin producing strains were more prevalent towards the end of the sampling period. M. botrys strains demonstrated substantial chemotype diversity throughout the sampling period, and to our knowledge, no previous studies has studied the great variation in MC production in Microcystis botrys in such detail.

Erik Selander
Dept. Marine Sciences, University of Gothenburg, Sweden

Sensing and signaling in marine diatoms

Diatoms constantly optimize resource allocation to variations in their biotic and abiotic environment. The expression of plastic traits is controlled by external cues such as nutrient concentration and specific cues from zooplankton grazers. The first predator cues have been identified as a group of polar lipids, copepodamides, from marine copepods. Copepodamides induce defensive traits in a diverse phytoplankton groups. Chain-forming diatoms split up into smaller units. Toxin producers increase toxin production. We use the copepodamide signaling systems to decode sensing and signaling in diatoms. The results suggest the involvement of a G protein coupled receptor proteins with cAMP second messenger driven cascades. The transcriptome shows a massive response to direct grazing but a much more subtle response to copepodamide signaling alone. Finally the we show that the defended phenotypes are significantly less grazed. Addition of naturally occurring concentrations of copeopdamides structure species composition in both pro-, and eukaryote plankton. We conclude that the structuring effect of zooplankton grazers in plankton communities is partly driven by indirect effects of chemical alarm signals rather than direct grazing.

Giannina Hattich,
GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany

It takes two to tango - How ecological and evolutionary changes shape future phytoplankton communities

Giannina SI Hattich1, Jorin Hamer1, Sivia Pulina1,2, Birte Matthiessen1
1 GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany
2 University of Sassari, Italy

Community property changes in response to changing nutrient scenarios in the world’s oceans are a combination of ecological species compositional changes and evolutionary genotype shifts. Our model system consists of nine genotypes, each of two functionally different and stably coexisting marine phytoplankton species, the diatom Chaetoceros affinis and the coccolithophore Emiliania huxleyi. Using this system, we assessed both, the ecological and evolutionary responses to different nutrient regimes (Redfield, P-limited and N-limited) and potential eco-evolutionary coupling. We present first findings from changing community properties and underlying community dynamics of a still ongoing long-term experiment. We further estimate the relative importance of species vs genotype compositional shifts, to explain differences in community properties among nutrient regimes. By linking potential eco-evolutionary dynamics, these findings will be essential to improve predictions on phytoplankton change in the light of altering ocean nutrient regimes.

Ingrid Sassenhagen,
Université du Littoral Côte d'Opale, France 

Protist interactions and community dynamics during early autumn in the Kerguelen region (Southern Ocean)

This study investigated in depth protist community composition and biotic interactions focusing on microplankton at four distinct sites around the Kerguelen Islands (Southern Ocean) after the summer phytoplankton bloom. Protist diversity in different size fractions, sampled with Niskin bottles and plankton nets, was assessed by sequencing of the V4 18S rDNA region. Combing different approaches, i.e. sequencing of different plankton size fractions, and isolation and sequencing of single cells, provided new insights into microbial interactions in protist communities. The communities displayed high variability, including short-term fluctuations in relative abundance of large protists (>35 μm) highlighted by the plankton net samples. Size fractionation of protist communities showed high concentrations of free Syndiniales spores but relatively few Syndiniales associated with microplankton, suggesting low parasitic infection in early autumn. Co-variance network analyses and sequencing of individually isolated single cells highlighted the important role of Rhizaria as consumers of a wide range of different diatom taxa. The data also supported the association of dominant diatom genera with several different Syndiniales clades suggesting a wider host range of these parasites than previously reported. These associations and the potential impact on carbon fluxes are discussed.

Jon Havenhand,
Department of Marine Sciences, University of Gothenburg, Sweden

Toxic Algae Silence Physiological Responses to Multiple Climate Drivers in a Tropical Marine Food Chain

Josefin Sefbom,
Department of Marine Sciences, University of Gothenburg, Sweden

Dispersal of antibiotic resistance mediated by the phycosphere, as a result of aquaculture activities in Southern India

Coastal regions in south India, especially in the east, are highly productive areas for aquaculture activities. Here we have investigated whether the use of antibiotics is still common practice to mitigate disease outbreaks, and whether antibiotic-resistant bacteria associated with planktonic organisms disperse to adjacent areas. During the winter of 2017/18 and 2019 we sampled the microbial communities of shrimp ponds and the adjacent water-ways. Using metagenomics we have characterized the bacterial communities, and looked for antibiotics-resistance genes (ARGs), within ponds stocked with the commercially important shrimp Penneaus vannamei. Based on the occurrence of specific ARGs found within ponds, using quantitative PCR we will then test whether these genes can be found in the samples collected from the adjacent estuaries and further down-stream. Due to that the coastal areas of these regions are highly oligotrophic, we believe that the phycosphere may provide as a carbon source and hence dispersal vector for heterotrophic bacteria carrying ARGs. There are studies that show that pathogenic marine bacteria can reach global spread this way and there is reason to assume that resistance may travel in the same way.

Luca Zoccarato,
IGB Berlin, Germany

Comparative whole-genome analysis of marine bacteria deciphers genomic signatures of functional traits promoting interactions with phytoplankton

Bacteria are responsible for half of the turnover of net global primary production in aquatic systems, enabled by the close coupling with autotrophic producers (e.g. diatoms and cyanobacteria). However, mechanistic studies investigating such direct interactions are restricted to a handful of representative model systems. Aiming to predict the ability of heterotrophic bacteria to interact with phytoplankton based on the sequences of their genomes, we functionally characterized the metabolic capacity (KEGG modules) as well as additional “interaction traits” (e.g. the production of secondary metabolites, secretion systems, siderophores and phytohormones) in the complete genomes of 473 marine bacteria. Genomes sharing common functional patterns were termed genome functional clusters (GFCs). Some interaction traits, such as the production of putative antimicrobial compounds, were widely distributed among all GFCs, whereas others (e.g. quorum sensing and the production of phytohormones) were more limited in their distribution. GFCs grouping α-proteobacteria and γ-proteobacteria genomes possessed the largest arsenals of putative interaction traits. These findings, which are broadly consistent with known interactions, suggest the existence of a much wider plethora of bacteria with an active role in phytoplankton-bacteria interactions than currently known. In addition, our genomic approach allows formulating predictions on interaction processes taking place in microbial communities which include members of the GFCs. As a case study, we tried to apply such analysis to the microbial communities associated with Skeletonema marinoi in the Baltic Sea.

Maria Kahlert,
Swedish University of Agricultural Sciences, Department of Aquatic Sciences and Assessment, Sweden

Exploring Patterns of Diatom Assemblages from Circumpolar Arctic Lakes & Streams.

The assessment of spatial and temporal trends in Arctic freshwater biota and their physical and biogeochemical habitat in response to a warming climate requires a large-scale harmonized monitoring program. The presented work, performed by the freshwater group of the Circumpolar Biodiversity Monitoring Plan (Arctic Council: Conservation of Arctic Flora and Fauna), is one of the first steps towards such a harmonized monitoring program. Using circum-Arctic diatom assemblage data, specific goals of this study include:

  1. establishing current and pre-industrial environmental conditions as reference points to guide future environmental monitoring programs, and
  2. understanding the historical context of diatom distributions.

Large-scale assessments of diatom distributions in Arctic regions are currently scarce, and detailed taxonomic studies tracking species compositional changes in both lakes and streams have yet to be undertaken. We used contemporary stream and lake data from ongoing monitoring programs, spot data from research projects, as well as surface sediment (modern) diatoms from paleolimnological studies to provide a spatial assessment of species distributions of the circum-Arctic region. Additionally, we analysed a large set of dated and “top-bottom” paleolimnological records to better describe historical background conditions on a circum-Arctic scale.

Marianne Ellegaard,
University College Copenhagen, Denmark

Diversity and survival of diatoms and other protist resting stages in an over 100-year old sediment archive from an Arctic fjord

Mariella Ferrante,
Stazione Zoologica Anton Dohrn, Italy

The fundamental role of sexual reproduction in diatom life cycles

Sexual reproduction plays a fundamental role in diatom life cycles. It contributes to increasing genetic diversity through meiotic recombination and represents the phase where large-sized cells are produced to counteract the cell size reduction process that characterizes these microalgae. With the aim to identify genes linked to the sexual phase of Skeletonema marinoi, we compared the expression level of transcripts in sexualized cells with that of large cells not competent for sex using RNA-seq. A set of genes involved in meiosis were found upregulated. Despite the fact that flagellate gametes were observed in the sample, we unexpectedly did not detect the expression of genes involved in the synthesis of flagella that were upregulated during sexual reproduction in another centric diatom, suggesting variations in the way flagella are built. We also carried out a comparison with the set of genes changing during the first phases of sexual reproduction of the pennate diatom Pseudo-nitzschia multistriata, revealing the existence of commonalities, including the strong upregulation of genes with an unknown function that we named Sex Induced Genes (SIG). Our results allow to define a panel of genes that can be used for the detection of diatom sexual reproduction in metatranscriptomic datasets. 

Marina Montresor,
Stazione Zoologica Anton Dohrn, Italy

High cell density and viral infection trigger formation of resting stages in the marine diatom Chaetoceros socialis

Angela Pelusi, Anna Godhe, Maria Immacolata Ferrante, Maurizio Ribera d’Alcalà, Kimberlee Thamatrakoln, Kay Bidle, Marina Montresor

Many diatoms have heteromorphic life cycles that include the formation of resting stages. These stages can increase the range of conditions in which species can survive, thus ensuring their persistence in time with important ecological implications for population dynamics. Although common to many species, cues and modality of resting stage formation remain unclear. Nitrogen starvation is reported as the most effective one in the laboratory; however, the link between spore formation and nitrogen depletion in the natural environment remains elusive.
Using the widespread marine diatom Chaetoceros socialis as model species, we tested additional factors that may play a role in inducing spore formation. Even though nitrogen depletion was confirmed to be the most effective trigger in laboratory conditions, resting stages were formed also when cell density was high but nutrients were not limiting and when cultures were grown in culture medium conditioned by high cell density. Chaetoceros socialis can be infected by a small RNA virus and we also tested if viral attack can induce a life cycle shift from vegetative cells to resting spores. Indeed significantly higher numbers of spores were produced in infected cultures as compared to the non-infected control. Our results suggest the presence of chemical cues that induce the formation of spores and also suggest that biological interactions, both between cells of the same species and between diatom cells and the virus, can play an important role in this process.

Mats Töpel
Department of Marine Sciences, University of Gothenburg, Sweden

The Skeletonema marinoi genome project

We have generated a reference genome sequence from Skeletonema marinoi strain R05AC as part of our work to establish this species as a new genetic model organism for marine diatoms. The genomic data has revealed peculiar genomic features of this strain, such as indications of partial genome duplication, and we are currently analyzing what implication these could have. Analysis of the sequence has resulted in the identification of approximately 22’000 unique genes of which 80% still have an unknown function. To functionally characterize these genes, and to shed light on the genetic mechanisms responsible for the global success of marine diatoms, a forward genetic approach has been developed which has resulted in a mutant library of ~600 lines currently being screened for divergent phenotypes.
A diatom genome project can generate a massive amount of bacterial sequence data which increases sequencing costs and complicates assembly and analysis. In this project we have managed to mediate this problem by also isolating individual bacteria associated with S. marinoi and analyzing their sensitivities to different antibiotics, thereby identifying an effective treatment less harmful to S. marinoi.

Olga Kourtchenko,
Department of Marine Sciences, University of Gothenburg, Sweden

Survivors of the sea: how diatom resting stages remain alive a 100 years embedded in sediment

Olga Kourtchenko (1), Elizabeth K. Robertson (1), Rickard Stenow (1), Björn Andersson (1), Matthew Pinder (1), Volker Bruchert (2), Helle Ploug (1), Mats Töpel (1), Anna Godhe (1†)

(1) Department of Marine Sciences, Gothenburg University, Göteborg, Sweden;
(2) Stockholm University, Stockholm, Sweden
† deceased

A common planktonic diatom Skeletonema marinoi can form resting stages, which remain viable in dark anoxic sediments for centuries. The cellular mechanisms facilitating such extended survivability are currently poorly understood. Our preliminary data suggests that S. marinoi cells maintain a certain level of metabolic activity during dormancy, as they were able to assimilate nitrate and ammonium under dark anoxic conditions (see Rickard Stenow’s poster). In the framework of the project “Survivors of the sea: how diatom resting stages remain alive a 100 years embedded in sediment”, we attempt to further investigate the diatom dark survival strategies and the cellular processes necessary for the durable exchange with the environment. We will use stable isotope incubations of relevant nutrients in combination with modern spectrometry techniques (SIMS, GC-IRMS/EA-IRMS) to reveal diatom-specific dark-active metabolic routes. These will be coupled to the transcriptional profiling studies using RNAseq analyses (see Matthew Pinder’s poster). Taken together, the results would help us better understand the functional pathways of the diatom resting stages survival in the context of their microhabitat.

Pierre De Wit
Department of Marine Sciences, University of Gothenburg, Sweden

Adaptation of a key phytoplankton species to anthropogenic stress over the last century

Old resting stages of phytoplankton stored in sediment can be germinated and used to assess temporal changes in both phenotype and genotype following adaptation to anthropogenic stress. We recovered 163 cells of the phytoplankton Skeletonema marinoi, originating from the 1930th to 2010, from an isotope-dated sediment core collected from a eutrophicated fjord. Each cell was revived and cultured to characterize its phenotype under different combinations of light and nutrient conditions, and genotyped for 52 genes involved in nutrient assimilation and light harvesting pathways. Recent strains had higher fitness in high- compared to low nutrient water, and were less sensitive to shifts in light intensity. Overall low genetic differentiation (FST ≈0.01) was accompanied by pronounced differences in 13% of the investigated genes (FST >0.2), with changes in 24 of the genes also correlating with phenotypic changes. This suggests that S. marinoi has evolved adaptations to increased eutrophication during the past century.

Sandra Lage
Stockholm University, Sweden

Allelopathic effects of Nodularia spumigena on Phaeodactylum tricornutum

Allelopathy, the release of extracellular compounds that inhibit the growth of other microorganisms, may be one factor contributing to the formation and/or maintenance of cyanobacterial blooms. We investigated the allelopathic effects of the cyanobacteria Nodularia spumigena, that frequently form mass-occurrences in the Baltic Sea, on the growth and photosynthetic activity of the diatom Phaeodactylum tricornutum. The two different species were grown under mono- and co-culture conditions; using an innovative co-culturing chamber, in which the species are physically separated but share a common culture medium allowing the diffusion of signal molecules. Additionally, we investigated the changes in N. spumigena cyanopeptides (namely spumigins, anabaenopeptins, aeruginosins and nodularin) profiles in response to interspecific interactions.

Valeria Villanova,
Department of Biological and Environmental Sciences, University of Gothenburg, Sweden

Mixotrophic metabolism in Skeletonema

Diatoms are unicellular eukaryotic microalgae and one of the most common and diverse type of marine phytoplankton. Thanks to a flexible cell metabolism, they dominate in environmental conditions normally unfavorable for photosynthesis, i.e. freezing seawater, low light intensity and short photoperiod. Moreover, diatoms are able to synthesize storage lipids (20-50% of cell dry weight) that can be used for production of renewable biomass and high-value fatty acids. However, the success of these microalgae as feedstock depends on lowering the production cost.
This project aims to develop mixotrophic cultivation (i.e. the simultaneous use of light, carbon dioxide and organic carbon for growth) to maximize outdoor productivity for selected strains from the Swedish west coast. The focus will be on the bloom-forming coastal diatom Skeletonema marinoi whose sequence annotation is ongoing, and the recent knowledge on mixotrophic growth of the model diatom Phaeodactylum tricornutum will be employed. The main objectives will be: i) using the bloom-forming S. marinoi to better understand diatoms’ mixotrophic metabolism; ii) exploring the optimal mixotrophic conditions for enhanced S. marinoi’s productivity; iii) investigating the S. marinoi’s industrial applications cultivated under mixotrophy. To achieve these objectives, an interdisciplinary approach including computational, biophysical, analytical and biotechnological methods will be employed.


  1. Adil Y.ousif Al-Handal
  2. Anders Alfjorden
  3. Björn Andersson
  4. Carl-Joar Karlsson
  5. Helle Ploug
  6. Kat Hodgkinson
  7. Klara Wolf
  8. Kristie Rigby
  9. Matt Pinder
  10. Rickard Stenow


Adil Yousif Al-Handal,
Department of Biological and Environmental Sciences, University of Gothenburg, Sweden.

Entomomanis annagodhei sp. nov., a new marine diatom (Bacillariophyceae)from the west coast of Sweden

A new species of the diatom genus Entomoneis was encountered in the coastal region of Kungälv. This species is named Entomoneis annagodhei sp. nov. after our friend and colleague Late Professor Anna Godhe as appreciation for her contribution to diatom research. The species is differentiated from all other members of Entomoneis by having a central area that extends bilaterally to form fascia reaching valve margins, a feature that has not been reported in the genus. It was common in the plankton and the benthos. A full description based on LM and SEM examination is given as well as comparison with other related taxa.

Anders Alfjorden,
Uppsala University, Sweden

What can cell cultures of oyster biopsies learn us of diatom lifecycles.

In a pilot project, during winter 2016/17, samples from young and adult flat oysters (Ostrea edulis) where collected in purpose to investigate presence of parasitic unicellular organisms within host tissues. Biopsies where collected from mantel, adductor muscle, heart, digestive gland and intestinal tract. Samples were inoculated in a thermoconstant room at Tjärnö Marine Laboratory at 10degrees with 16 hour light period/day. During a period for 2-4 week (November-December -16) inoculated biopsies were investigated by inverted microscope every second day for cell development and presence of new emerging organisms. During these investigations’ microscopical findings of Thalassiosira sp. cells developing from single cells to triple cell chains within a period of 1,5 hours was detected. These findings where seen within wells of inoculates of muscle biopsies. In intestinal samples a variety of Diatoms were detected. The viability of these cells where tested by chloroplasts light emission after blue light exposure. These findings indicate strategies of diatom survival and resuspension of viable diatom cells from feeding oyster after digestion.

This work have been presented as a bachelor thesis winter 2016/17 under the supervision of Anna Godhe and Kristina Sundell / GU.

Björn Andersson,
Department of Marine Sciences, University of Gothenburg, Sweden

Evolutionary and ecological implications of strain variability in heavy metal tolerance amongst Baltic Sea diatoms

Björn Andersson1, Olof Berglund2, Helena L. Filipsson3, Karin Rengefors2
Anna Godhe1

(1University of Gothenburg, Department of Marine Sciences, 2Lund University, Department of Biology, 3Lund University, Department of Geology)

Microalgae have short generation times, flexibility in reproductive strategies, and large standing genetic diversity. These traits facilitate rapid changes in community structure and evolution. Here we compare intra and inter-specific toxic tolerance to against 7 heavy metals amongst diatom strains of Skeletonema marinoi and Thalassiosira baltica. The stains were revived from sediment resting stages at two Baltic sea location; one affected by mining pollution and one reference site. We found that T. baltica was more tolerant to Ag and Cu, whereas S. marinoi was more tolerant to Cd and Pb. This suggests that mining discharge can have different effects on the structure of phytoplankton assemblages, depending on the composition of metals. At the mining affected site S. marinoi strains were on average more tolerant to all 7 metals (p <0.05 for Cu and Co only, N=5), suggesting that this species has evolved metal tolerance at this location. We further investigated Cu tolerance using long-term (42 days) artificial selection experiments on assembled S. marinoi populations (N=30). Both plasticity and inherent strain variability in tolerance affected the development of Cu tolerance. In the future we aim to identify genetic regions associated with Cu tolerance using a Genome Wide Association Study.

Carl-Joar Karlsson,
Department of Mathematical Sciences, GU/Chalmers, Sweden

Game theoretic explanation of intra-specific diversity among replicating microbes

This poster presents an overview of a project in mathematical ecology called "Game theoretic explanation of intra-specific diversity among replicating microbes". We will study the evolution of behavior in our model, and therefore, I am seeking collaborators that can provide expertise knowledge and experimental tests of our predictions.

Helle Ploug,
Department of Marine Sciences, University of Gothenburg, Sweden

High diversity in carbon to nitrogen ratios at clone and single cell level in the chain-forming diatom Skeletonema across a century

Malin Olofsson, Olga Kourtchenko, Eva-Maria Zetsche, Hannah K. Marchant, Martin J. Whitehouse, Anna Godhe, and Helle Ploug

Almost a century ago Redfield discovered a relatively constant ratio between carbon, nitrogen, and phosphorus in particulate organic matter, and nitrogen and phosphorus of dissolved nutrients in seawater. Since then, the riverine export of nitrogen to the ocean has increased 20-fold. The common planktonic diatom Skeletonema marinoi forms resting stages in sediments for future blooms. We germinated unique genotypes from resting stages originating from isotope-dated sediment layers (15 and 80 y old) in a eutrophied fjord, and determined their cellular carbon, nitrogen, and phosphorus ratio on a clone specific level depending on nutrient availability in the water. Using secondary ion mass spectrometry (SIMS) combined with stable isotopic tracers, we show that the cell-specific carbon and nitrogen assimilation rates varies one order of magnitude on a single cell level, but are significantly correlated during the exponential growth phase resulting in a constant assimilation quota in cells with identical genotypes. The assimilation quota varies largely between different clones independent of age. We argue that the success of S. marinoi in coastal water may be explained by its high diversity of nutrient demand not only among clones, but also on the single cell level, whereby the population can sustain and adapt to eutrophication.

Kat Hodgkinson,
University of East Anglia, UK

Many diatoms rapidly adapt to changing environmental conditions.

Their adaptive evolutionary potential may in part be due to their intra-specific variety in genomic size and structure. In Skeletonema marinoi, the recycling of genetic diversity from benthic resting stages is also thought to contribute to their success in colonising a range of coastal habitats. This mechanism makes S. marinoi ideal for population and evolutionary genomics, as  as their adaptive evolutionary change can be studied by reviving dormant cell lines. We have successfully revived lines from different spatial and temporal scales, including lines from power plant waters that experienced rapid temperature change. We will construct full genome assemblies of these lines and use their transcriptomes to understand how S. marinoi adapted and evolved to benthic survival in a changing climate. Preliminary k-mer analysis suggests potential variety in genome size and ploidy. Genetic diversity varies spatially and temporally between lines and divergent content is found in both heterozygous and homozygous regions. Additionally, triple-represented content from a geographically isolated line is conserved across all other diploid lines. These early results provide a hopeful basis to expand our evolutionary analysis into.

Klara Wolf,
Alfred-Wegener Institute, Bremerhaven, Germany

Revealing population and selection dynamics in an Arctic diatom to assess adaptive potential to climate change

Arctic phytoplankton, being the base of the foodweb in one of the most rapidly changing regions on the planet, is especially faced with the large transformations caused by climate change, but has been found to be largely resilient towards them. We tried to tackle the question how this resilience may be explained with specific focus on the role and functioning of intraspecific selection and population dynamics of the diatom Thalassiosira hyalina. Selective processes driving intraspecific population dynamics in phytoplankton are methodologically still difficult to resolve. We therefore established new avenues for the use of microsatellites as an efficient population genetic tool, allowing the analysis of bulk community samples in experimental and natural contexts at close temporal resolution. In this study, we were able to resolve detailed selection dynamics in simplified diatom populations and found that their composition was reproducibly altered by the applied environmental conditions. Furthermore, in experiments with natural populations as well as in field samples from two spring blooms, our new method, microsatellite poolSeq barcoding (MPB), revealed a surprising allelic stability in diverse populations over time, but also sudden shifts of their allelic composition under specific environmental treatments.

Kristie Rigby,
Department of Marine Sciences, University of Gothenburg, Sweden

Unicellular marine phytoplankton have to rely on chemical signals to evade predation.

Several taxa respond to copepodamides, a group of polar lipids released from copepod grazers. Responding algae launch a range of defensive traits to avoid predation. These include toxin production, colony size shrinkage and increased bioluminescence. As a consequence the presence of copepod grazers have been suggested to produce large scale trait mediated cascades in the ocean. However, it is not known if copepodamides affects phytoplankton in general or only the few published examples. Here I specificially test the effect of copepodamides on chain formation in marine diatoms. I exposed Thalassiosira rotula, Chaetoceros affinis and Chaetoceros curvisetus chain forming diatoms to copepodamides and monitored their chain length. The results coupled with a grazing experiment clearly show that chain length is regulated as a form of inducible defence mechanism against predation. Thereby suggesting that copepodamides could function as a general alarm signal across multiple taxa.

Matt Pinder,
Department of Marine Sciences, University of Gothenburg, Sweden

Survivors of the Sea: Using Transcriptomics to Elucidate the Survival Strategies of Century-Old Diatoms in Sediment

Diatom resting stages are produced in response to unfavourable conditions, allowing the diatoms to remain dormant in the sediment and germinate when more favourable conditions present themselves, a strategy which also helps to anchor the population in the area. Resting stages of the chain-forming diatom Skeletonema marinoi can be revived and cultured after up to a century in this dark, anoxic state, however the exact mechanisms and metabolic pathways behind this long-term survival are currently unclear. One clue from preliminary results is that resting stages assimilate nitrogen, indicating that they are not as closed off to their environment as previously believed. Using RNA sequencing of both vegetative and resting stage cells, we intend to perform differential expression analysis to identify the genes being expressed during dormancy to help elucidate S. marinoi’s methods of survival. As a large proportion of the gene models identified in the S. marinoi genome are of unknown function, we hope that this project will work synergistically with the other projects surrounding this diatom in order to improve our understanding of the species.

Rickard Stenow,
Department of Marine Sciences, University of Gothenburg, Sweden

Resting stages of Skeletonema marinoi can assimilate inorganic nitrogen

The planktonic marine diatom Skeletonema marinoi forms resting stages, which can survive for decades buried in aphotic, anoxic sediments and resume growth when re-exposed to light and nutrients. The mechanisms by which they maintain cell viability during dormancy are currently poorly known. Here, we investigated cell specific nitrogen (N) and carbon (C) assimilation and survival rate in resting stages of three S. marinoi strains. Resting stages were incubated with stable isotopes of N, in the form of 15N-ammonium (NH4+) or -nitrate (NO3-) and C as 13C-bicarbonate (HCO3-) under dark and anoxic conditions for two months. Survival varied between <0.1% and 47.6% among the three different S. marinoi strains. Using Secondary Ion Mass Spectrometry (SIMS) we quantified assimilation of labelled C and N from the ambient environment within the resting stages. Dark fixation of C was insignificant across all strains. Significant assimilation of 15N-NO3- and 15N-NH4+, occurred in all three S. marinoi strains with average N- turnover times ranging between 77 and 380 years. This activity may explain their well-documented long survival and swift resumption of vegetative growth after dormancy in dark and anoxic sediments.

Page Manager: Eva Marie Rödström|Last update: 11/4/2019

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