Diatom Frustules Nanostructure in Pelagic and Benthic Environments

International audienceDiatoms are an important group of eukaryotic microalgae with a siliceous cell wall, the frustule. Diatoms are traditionally subdivided into two sub-classes, namely centric diatoms with a radial symmetry and pennate diatoms with a bilateral symmetry. These two groups of diatoms have usually biotope preferences, with centric diatoms dominating the pelagic environments, whereas the benthic habitats are mostly inhabited by pennate diatoms. The question of how the morphology of diatoms (centric versus pennate) or the ultrastructure of the frustule could be driven by ecological constrains remains unclear. For example, some studies have suggested that the structure of the diatom frustule could play a role in the light harvesting performances. In this work, we studied the variations of the diatom frustules nanostructure in several benthic and pelagic species inhabiting the same coastal ecosystem, particularly the ultrastructure that includes the distribution and size of the frustule pores. Although the species studied here experience different ecological constrains in term of light, we found no significant differences between benthic and pelagic species, in either the size of the pores (average =285 (+/- 108) nm) or the distance between them (average =234 (+/- 87) nm). Moreover, the intra-species variability was sometimes larger than the variability observed between cells from different genera. We concluded that the pore morphometry is controlled by a combination of genetically-driven processes of bio-mineralization, and episodic variations in environmental growth conditions which influence the chemical precipitation of silica within the cells

Are upwelling systems an underestimated source of omega-3 in the ocean? The case of the southern Benguela upwelling system

The Benguela Upwelling System (BUS) is one of the world’s most productive ecosystems, supporting globally relevant pelagic fisheries. BUS marine community can change as a function of nutrients and omega-3 long chain polyunsaturated fatty acids (hereafter, omega-3) availability. Phytoplankton growth is supported by upwelled nitrate, a new source of nitrogen (N), or by recycled N forms such as ammonium. Preferential assimilation of one N form over another may lead to differences in omega-3 production between high and low food-quality species. This study evaluates how upwelling and the N source(s) used by phytoplankton influence omega-3 production. Sampling was conducted in the BUS at an anchor station sampled daily for 10 consecutive days. An upwelling event on days 5-6-7 supplied high concentrations of nutrients to surface waters, while pre- and post- upwelling the water column was well-stratified with low nutrient concentrations. Omega-3 and phytoplankton concentrations declined to ⁓zero during the upwelling event. Nanoplankton (2.7-10µm) were responsible for most of the productivity (30-95%) and relied on nitrate for their growth. Omega-3 concentrations at the surface reached peaks of 215.5 and 175.3µgL-1 pre- and post-upwelling, which were up to 10-times higher than previous measurements from the BUS. Pre-upwelling, non-diatom trophic markers were dominant, with a rapid switch (over just two days) to diatom trophic markers post-upwelling. This study defines the key role of upwelling in promoting phytoplankton omega-3 production, which is tightly coupled to the introduction of new-N during upwelling. The high concentrations of omega-3 reported suggest that global omega-3 production is largely underestimated

Low-temperature amino-based catalyst activation for on-demand polyurethane synthesis

A new latent catalyst, based on 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), has been specifically designed to be thermally deprotected at low temperature. More generally, specific isocyanurates based on the reaction of two substituted isocyanates and DBN are used as pre-catalyst for polyurethane synthesis. The activation temperature of the pre-catalysts is determined by DSC and resulting free catalysts activity is demonstrated through a catalysis cycle on a PU model reaction