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Résumé de la communication de Pascal Jean LOPEZ (CNRS, Museum National d’Histoire Naturelle, Paris, France) donnée à l’occasion du séminaire Les constructions en milieu marin / Constructions in marine environment du 14 au 19 mars 2016Silicon is the second most abundant element on earth, with about 80% of the earth crust and mantle made of silicates. Silicon is also involved in the biogeochemical cycles of several important compounds, including atmospheric carbon dioxide (CO2) and nitrogen (N2). It is therefore rather surprising that most solid biomaterials such as shells, bones or teeth are made of calcium carbonate or phosphates rather than silica. Actually, silica glasses are very common materials. They are widely used for making bottles, windows or fibers.A few centuries ago, Charles Darwin was writin: 'few objects are more beautiful than the minute siliceous cases of diatom'. It is the molecular research in diatoms over the last two decades that had helped us to start to understand how a living cell can make a silica skeleton. First silicic acidhas to be transported inside the cells where condensation can occur. The first demonstration of the transport of silicic acid (named SITs) inside a living cell was obtained from a gene isolated from a marine diatom in the early 90's. It's now well known that fresh or marine water diatoms regulate the expression of SITs as a function of the availability and concentration of silicic acid in the medium and the period during their cell cycle. Genes showing high homology to diatoms SITs have recently been identified in siliceous Synurophyceae algae and in siliceous loricate Choanoflagellates, suggesting both horizontal and vertical gene transfer.The formation of silica structures was shown in diatoms to involve organic molecules, even if information on their diversity, the ratio of organic molecules to Si, and their precise roles in the polycondensation process are still missing. However a number of proteins (silaffins, silcidins, cingulins...) were shown to be embedded within the silica matrix or directly attached to it, as well as other organic molecules like long chain polyamines (LCPA), polysaccharides (i.e., chitin) and probably lipids. The morphologically aestetic but complex biosilica structures formed by diatoms are assembled inside a specific silica deposition vesicle, named SDV. The confinement of amorphous precursors inside a specialized membrane-bound compartment allow to control the conditions of the polycondensation process (i.e., regulation of the pH), the dynamic of the incorporation of the organic and mineral fractions, and to regulate the three-dimensional assembly through a phase separation process that might explain the hierarchical porous nano-patterning of biosilica. Alternative a combination of alternative models like diffusion limited aggregation, are likely to be important to be able to explain the regular and complex pattern of diatom frustules. The role of the cytoskeleton was also proposed to guide the assembly or the deposition of biomolecules.Many developments have been proposed that are derived from the knowledge learn on diatom biomolecular process of biomineralization or based on the thecae themselves. For example, chemically modified replicates of diatom frutules, or organic compounds extracted from diatoms biosilica have been used to develop strategies for protein encapsulation or biosensors. Recently porous diatoms frustules have also been considered for the production of nanostructured materials that could be used in photonic industry.Summary