Project description:Intense bottom-ice algal blooms, often dominated by diatoms, are an important source of food for grazers, organic matter for export during sea ice melt, and dissolved organic carbon. Sea-ice diatoms have a number of adaptations, including accumulation of compatible solutes, that allow them to inhabit this highly variable environment characterized by extremes in temperature, salinity, and light. In addition to protecting them from extreme conditions, these compounds present a labile, nutrient-rich source of organic matter and include precursors to climate active compounds (e.g. DMS), which are likely regulated with environmental change. Here, intracellular concentrations of 45 metabolites were quantified in three sea-ice diatom species and were compared to two temperate diatom species, with a focus on compatible solutes and free amino acid pools. There was a large diversity of metabolite concentrations between diatoms with no clear pattern identifiable for sea-ice species. Concentrations of some compatible solutes (isethionic acid, homarine) approached 1 M in the sea-ice diatoms, Fragilariopsis cylindrus and Navicula cf. perminuta, but not in the larger sea-ice diatom, Nitzschia lecointei or in the temperate diatom species. The differential use of compatible solutes in sea-ice diatoms suggest different adaptive strategies and highlights which small organic compounds may be important in polar biogeochemical cycles.
Project description:The diatoms Thalassiosira hyalina and Nitzschia frigida are important members of Arctic pelagic (open-water) and sympagic (ice-associated) microalgal communities. We investigated here the molecular mechanisms these algae apply to cope with abrupt high light exposure (Shift from 20 to 380 µmol photons m-2 s-1, resembling upwelling or ice break-up). Experiments were done under contemporary as well as future pCO2 (400 vs. 1000 µatm) to investigate whether [CO2] or pH modulate the reactions to high light intensities. After proper acclimation to the low-light regime, cells were sampled (= 0 hours), then exposed to the high-light treatment expression patterns were followed over 120h. Transcriptomic data were discussed also in the light of an accompanying physiological dataset from the same experiment (Ane Kvernvik et al. in prep).
Project description:Sea-ice algae provide an important source of primary production in polar regions, yet we have limited understanding of their responses to the seasonal cycling of temperature and salinity. Using a targeted liquid chromatography-mass spectrometry-based metabolomics approach, we found that axenic cultures of the Antarctic sea-ice diatom, Nitzschia lecointei, displayed large differences in their metabolomes when grown in a matrix of conditions that included temperatures of –1 and 4°C, and salinities of 32 and 41, despite relatively small changes in growth rate. Temperature exerted a greater effect than salinity on cellular metabolite pool sizes, though the N- or S-containing compatible solutes, 2,3-dihydroxypropane-1-sulfonate (DHPS), glycine betaine (GBT), dimethylsulfoniopropionate (DMSP), and proline responded strongly to both temperature and salinity, suggesting complexity in their control. We saw the largest (> 4 fold) response to salinity for proline. DHPS, a rarely studied but potential compatible solute, reached the highest intracellular compatible solute concentrations of ~ 85 mM. When comparing the culture findings to natural Arctic sea-ice diatom communities, we found extensive overlap in metabolite profiles, highlighting the relevance of culture-based studies to probe environmental questions. Large changes in sea-ice diatom metabolomes and compatible solutes over a seasonal cycle could be significant components of biogeochemical cycling within sea ice.