The molecular life of diatoms

Diatoms are unicellular photosynthetic eukaryotes that are arguably the most species-rich group of algae, having conquered most aquatic habitats since their major diversification around 65 million years ago (Bowler et al., 2010). They play a major role in the functioning of the global ecosystem, e.g., in silica and carbon biogeochemical cycles (Tréguer and De La Rocha, 2013 and Field et al., 1998). They have a complex evolutionary history, and like other chromalveolates are believed to be derived from a serial secondary endosymbiosis involving both green and red algae combining with a eukaryotic heterotrophic host cell (Moustafa et al., 2009). Their rigid cell wall has constrained them to acquire an unusual mode of cell division, with mitotically-derived daughter cells becoming progressively smaller until they reach a critical size threshold, following which they must undergo sexual reproduction for size restoration (Lewis, 1984 and Chepurnov et al., 2004). While many species are planktonic, the majority are benthic and can stick to virtually any surface. Many of these can move by gliding, a process mediated by the extrusion of polysaccharides from a slit in the cell wall known as the raphe (Edgar and Pickett-Heaps, 1984).