Diatom Frustules Nanostructure in Pelagic and Benthic Environments

Abstract

Diatoms 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.