Diversity and abundance of bolidophyceae (Heterokonta) in two oceanic regions

The diversity and abundance of the Bolidophyceae (Heterokonta), a newly des cribed picoplanktonic algal class which is a sister group to the diatoms, w as assessed in the equatorial Pacific Ocean and in the Mediterranean Sea by culture isolation, molecular biology techniques, and pigment analyses. Eig ht strains of Bolidophyceae were isolated in culture from different mesotro phic and oligotrophic areas. The corresponding small subunit (SSU) rRNA gen e sequences allowed us to design two probes specific for the Bolidophyceae. These probes have been used in natural samples (i) to selectively amplify and detect Bolidophyceae sequences and (ii) to quantify the relative abunda nce of Bolidophyceae within the picoeukaryote community. Sequences availabl e to date indicate that the class Bolidophyceae comprises at least three di fferent clades, two corresponding to the previously described species Bolid omonas pacifica and Bolidomonas mediterranea and the third one correspondin g to a subspecies of B. pacifica. Amplification of the SSU rRNA gene from n atural samples with universal primers and hybridization using a Bolidomonas -specific probe followed by a eukaryote-specific probe allowed us to estima te the contribution of the Bolidophyceae to the eukaryotic DNA in both Paci fic and Mediterranean waters to be lower than 1%. Similarly, high-performan ce liquid chromatography analyses of fucoxanthin, the major carotenoid pres ent in Bolidophyceae, indicated that less than 4% of the total chlorophyll a in the picoplanktonic fraction in the equatorial Pacific was due to Bolid ophyceae. Consequently, although strains of Bolidophyceae have been isolate d from samples collected at several stations, this new class seems to have been a minor component of the natural picoeukaryotic populations in the eco systems investigated, at least during the periods sampled.