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. 2004 Jul;70(7):4064-72.
doi: 10.1128/AEM.70.7.4064-4072.2004.

A single species, Micromonas pusilla (Prasinophyceae), dominates the eukaryotic picoplankton in the Western English Channel

Fabrice Not  1 , Mikel Latasa, Dominique Marie, Thierry Cariou, Daniel Vaulot, Nathalie Simon
Affiliations

A single species, Micromonas pusilla (Prasinophyceae), dominates the eukaryotic picoplankton in the Western English Channel

Fabrice Not et al. Appl Environ Microbiol. 2004 Jul.

Abstract

The class Prasinophyceae (Chlorophyta) contains several photosynthetic picoeukaryotic species described from cultured isolates. The ecology of these organisms and their contributions to the picoeukaryotic community in aquatic ecosystems have received little consideration. We have designed and tested eight new 18S ribosomal DNA oligonucleotide probes specific for different Prasinophyceae clades, genera, and species. Using fluorescent in situ hybridization associated with tyramide signal amplification, these probes, along with more general probes, have been applied to samples from a marine coastal site off Roscoff (France) collected every 2 weeks between July 2000 and September 2001. The abundance of eukaryotic picoplankton remained high (>10(3) cells ml(-1)) during the sampling period, with maxima in summer (up to 2 x 10(4) cells ml(-1)), and a single green algal species, Micromonas pusilla (Prasinophyceae), dominated the community all year round. Members of the order Prasinococcales and the species Bathycoccus prasinos (Mamiellales) displayed sporadic occurrences, while the abundances of all other Prasinophyceae groups targeted remained negligible.

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Figures

FIG. 1.
FIG. 1.
Phylogenetic tree of the Prasinophyceae obtained by the neighbor-joining method and based on analyses of complete 18S rRNA gene sequences. The specificities of the different probes designed in this study are presented. The clades were named according to the system of Guillou et al. (8). The numbers on the branches correspond to bootstrap values (done on 1,000 replicates).
FIG. 2.
FIG. 2.
Variations in temperature and phosphate and nitrate concentrations at the ASTAN station between July 2000 and September 2001.
FIG. 3.
FIG. 3.
(A) Variations in Chl a biomass as measured by HPLC (total <200-μm and fraction <3-μm) at the ASTAN station. (B) Contributions of the division Chlorophyta and of the orders Mamiellales, Prasinococcales, and Pseudoscourfieldiales to the picoplankton fraction (<3-μm diameter) according to the CHEMTAX algorithm applied to HPLC data.
FIG. 4.
FIG. 4.
Abundances (number of cells ml−1) of photosynthetic picoplankton off Roscoff (western English Channel) between July 2000 and September 2001. The average percentages over the time series of the different groups are represented in pie charts. (A) Picoeukaryotic photosynthetic cells detected by flow cytometry counts (Flow Cytometry); picoeukaryotic cells targeted by the mix of the general probes EUK1209R, CHLO01, and NCHLO01 (EUK1209R+CHLO01+NCHLO01); and cells belonging to the division Chlorophyta detected by the probe CHLO02 (CHLO02). (B) Cells targeted by the probe CHLO02 and cells detected by the probes specific for the clades PRAS01, PRAS03, PRAS04, PRAS05, and PRAS06. (C) Cells targeted by the probe specific for Mamiellales (PRAS04) and cells detected by the probes (MICRO01, BATHY01, and OSTREO01) specific for the species and genera.
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References

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