Applied and Environmental Microbiology, October 1999, p. 4528-4536, Vol. 65, No. 10
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Station Biologique de Roscoff,
Received 10 May 1999/Accepted 5 August 1999
The diversity and abundance of the Bolidophyceae (Heterokonta), a
newly described picoplanktonic algal class which is a sister group to
the diatoms, was assessed in the equatorial Pacific Ocean and in the
Mediterranean Sea by culture isolation, molecular biology techniques,
and pigment analyses. Eight strains of Bolidophyceae were isolated in
culture from different mesotrophic and oligotrophic areas. The
corresponding small subunit (SSU) rRNA gene 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 abundance of
Bolidophyceae within the picoeukaryote community. Sequences available
to date indicate that the class Bolidophyceae comprises at least three
different clades, two corresponding to the previously described species
Bolidomonas pacifica and Bolidomonas mediterranea and the third one corresponding to a subspecies of B. pacifica. Amplification of the SSU rRNA gene from
natural samples with universal primers and hybridization using a
Bolidomonas-specific probe followed by a eukaryote-specific
probe allowed us to estimate the contribution of the Bolidophyceae to
the eukaryotic DNA in both Pacific and Mediterranean waters to be lower
than 1%. Similarly, high-performance liquid chromatography analyses of
fucoxanthin, the major carotenoid present in Bolidophyceae, indicated
that less than 4% of the total chlorophyll a in the
picoplanktonic fraction in the equatorial Pacific was due to
Bolidophyceae. Consequently, although strains of Bolidophyceae have
been isolated from samples collected at several stations, this new
class seems to have been a minor component of the natural
picoeukaryotic populations in the ecosystems investigated, at least
during the periods sampled.
*
Corresponding author. Mailing address: Station
Biologique, BP 74, F-29682 Roscoff Cedex, France. Phone: (33) 2 98 29 23 14. Fax: (33) 2 98 29 23 24. E-mail:
lguillou{at}sb-roscoff.fr.
Present address: Universität zu Köln, Botanisches
Institut, Lehrstuhl I, 50931 Köln, Germany.
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