PHYLOGENETIC ANALYSIS AND GENOME SIZE OF OSTREOCOCCUS-TAURI (CHLOROPHYTA, PRASINOPHYCEAE)

Ostreococcus tauri Courties et Chretiennot-Dinet is the smallest descr ibed autotrophic eukaryote dominating the phytoplanktonic assemblage o f the marine Mediterranean Thau lagoon (France). Its taxonomic positio n was partly elucidated from ultrastructure and high-pressure liquid c hromatography (HLPC) pigment analysis. The sequence analysis of the 18 S rDNA gene of O. tauri measured here is available in EMBL Nucleotide Sequence Database (accession number: Y15814) and allowed to clarify it s phylogenetic position. O. tauri belongs to the Prasinophyceae and ap pears very close to Mantoniella, a typical scaly Prasinophyceae, morph ologically very different from the naked and coccoid Ostreococcus. An electrophoretic analysis of O. tauri shows that the nucleus contains 1 0.20 mbp. This small genome fragmented into 14 chromosomes ranging in size from 300 to 1500 kbp, confirms the minimalist characteristics of Ostreococcus tauri.