Diatom

A diatom is a unicellular eukaryotic alga characterized by a silica-containing cell wall called a frustule. The wall typically has two overlapping portions, making the organism a striking example of biologically constructed mineral architecture. Diatoms contribute to photosynthetic production and to movement of silicon through aquatic ecosystems.

Experiments on marine bacterial assemblages connected decay of diatom organic material to accelerated dissolution of the silica wall. ^[ref] The biological and mineral parts of a dead cell therefore do not have independent fates. Removing or altering the surrounding organic material can change how rapidly the mineral component is returned to the dissolved pool.

A frustule is the intricately patterned, silica-containing cell wall of a diatom. Its two principal overlapping halves fit rather like a lid and a box, with connecting bands. Pores and ridges differ among diatom groups, making the mineral structure useful in microscopic identification.

How can a biological cell make a patterned mineral structure under mild conditions? Isolated diatom peptides called silaffins caused silica nanospheres to form rapidly when added to a solution of silicic acid. This demonstrated that cellular organic components can directly promote mineral formation.^[ref] The experiment accounts for one chemical capacity; a complete frustule also requires control over where that capacity acts and how the resulting material is organized.