The Biochemistry of Silica Formation in Diatoms

Manfred Sumper

Naturwissenschaftliche Fakultät, University of Regensburg, Universitätsstraße 31, D-93053 Regensburg, Germany

e-mail: Manfred.Sumper@vkl.uni-regensburg.de
 

Diatoms are eucaryotic, unicellular algae that are ubiquitously present in almost any water habitat on earth. In the oceans diatoms dominate phytoplankton blooms and thus are among the most important primary producers on our planet. Apart from their ecological significance, diatoms are well known for the intricate geometries and patterns of their silica-based cell walls. The structures of diatom cell walls are species specific and become precisely reproduced during each cell division cycle, indicating the genetic control of this biomineralization. Therefore, the formation of the diatom cell wall has been regarded as a paradigm for controlled production of nanostructured silica. However, the mechanisms allowing biosilicification to proceed at ambient temperature at high rates have remained enigmatic.

Recently, we have shown that a set of highly cationic peptides (called silaffins) isolated from diatom shells are able to generate networks of silica nanospheres within seconds when added to a solution of silicic acid. Different silaffin species produce different morphologies of the precipitated silica. Silaffins contain covalently modified Lys-Lys elements. One of these lysine residues bears a novel type of protein modification, a polyamine consisting of 6-11 repeats of the N-methyl-propylamine unit. In addition to the silaffins, additional polyamine-containing substances have been identified that appear to be involved in the control of biosilica morphology.

Scanning electron microscopic analysis of diatom shells isolated in statu nascendi provide insights into the processes of pattern formation in biosilica. A model will be discussed that explains production of nanostructured biosilica in diatoms on the basis of these experimental results.