Reduction to essentials: Ostreococcus, the smallest free-living eukaryote
Abstract How can a complex eukaryotic cell reduce its cell size to bacterial dimensions? The microalga Ostreococcus (ca. 0.8–1.3 µm diameter) holds the record in miniaturization among free-living eukaryotes. In this article Ostreococcus is viewed in the evolutionary context of reductive evolution, with special reference to related microalgae in the class Mamiellophyceae, some of which are also extremely small-sized (Micromonas, Bathycoccus). Several aspects of cell compaction are discussed, e.g. mitosis, sexual reproduction, genome reduction, and simplification of cell processes. By studying biological processes in Ostreococcus we can learn, what is really essential for a system’s function. Thus, Ostreococcus has a great potential as highly simplified model organism for plant cell biology, supplementing the already established model organisms.