Ostreococcus tauri

The marine green alga Ostreococcus tauri was isolated only recently (in 1994); with a diameter of about 1 ^m it is the smallest free-living eukaryote known (Courties et al. 1994). It is a member of an ancient group of green algae, Prasinophyceae, that dominated the Paleozoic oceans but are now only minor contributors to marine productivity. Phylogenetically, the Prasinophyceae are positioned at the base of the primary green algal clade. O. tauri cells lack cell walls, are nonflagellated, and contain only a single mitochondrion and chloroplast (Chretiennot-Dinet et al. 1995). These properties together with its evolutionary position attracted an interest which yielded the completion of sequencing of O. taurfs strikingly small (approx. 13 Mb) genome (Derelle et al. 2006).

Since O. tauri is a promising new algal model, efforts have been made to establish/improve both the cultivation conditions and conditions for synchronizing the cultures (Courties et al. 1998; Farinas et al. 2006). O. tauri divides by binary fission (in contrast to the multiple fission of C. reinhardtii and S. quadricauda) with chloroplast dividing first during S phase, followed by division of the mitochondrion and nucleus (Farinas et al. 2006). Like C. reinhardtii and S. quadricauda, O. tauri can be synchronized by alternating light/dark regimes. Due to its binary fission cell cycle, synchronization is far more difficult (maximum of 35% of cells in S phase). However, an increase in the cell synchrony can be achieved by application of hydroxyurea, aphidicolin, or propyzamide (Farinas et al. 2006).

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