Silica pattern formation in diatoms: species-specific polyamine biosynthesis.

Diatoms are eukaryotic, unicellular algae that are well known for the intricate architecture of their silica-based cell walls. Species identification is mainly based on variations of their hierarchically organized silica structures. Particularly striking silica frameworks are found among diatoms that belong to the genus Coscinodiscus. Recent work indicates an important role for long-chain polyamines in guiding silica precipitation as well as in silica-pattern formation. Here we demonstrate that polyamines, even if isolated from closely related diatom species, exhibit substantial structural differences. Structural variations include the overall chain length, the degree of methylation, positions of secondary amino functionalities, and, unexpectedly, site-specific incorporation of a quaternary ammonium functionality. These findings support a specific role for polyamines in creating silica nanostructures.