title: Unexpected importance of potential parasites in the composition of the freshwater small-eukaryote community.
abstract: The diversity of small eukaryotes (0.2 to 5 mum) in a mesotrophic lake (Lake Bourget) was investigated using 18S rRNA gene library construction and fluorescent in situ hybridization coupled with tyramide signal amplification (TSA-FISH). Samples collected from the epilimnion on two dates were used to extend a data set previously obtained using similar approaches for lakes with a range of trophic types. A high level of diversity was recorded for this system with intermediate trophic status, and the main sequences from Lake Bourget were affiliated with ciliates (maximum, 19% of the operational taxonomic units [OTUs]), cryptophytes (33%), stramenopiles (13.2%), and cercozoa (9%). Although the comparison of TSA-FISH results and clone libraries suggested that the level of Chlorophyceae may have been underestimated using PCR with 18S rRNA primers, heterotrophic organisms dominated the small-eukaryote assemblage. We found that a large fraction of the sequences belonged to potential parasites of freshwater phytoplankton, including sequences affiliated with fungi and Perkinsozoa. On average, these sequences represented 30% of the OTUs (40% of the clones) obtained for each of two dates for Lake Bourget. Our results provide information on lacustrine small-eukaryote diversity and structure, adding to the phylogenetic data available for lakes with various trophic types.
authors: Université Blaise Pascal, Laboratoire de Biologie des Protistes, UMR CNRS 6023, 63117 Aubière, France.
authors: Cécile
authors: C
authors: Lepère
authors: Isabelle
authors: I
authors: Domaizon
authors: Didier
authors: D
authors: Debroas
mesh_terms: D044822:Biodiversity; D048028:DNA, Algal / Q000737:chemistry / Q000235:genetics*; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics*; D016054:DNA, Protozoan / Q000737:chemistry / Q000235:genetics*; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D005618:Fresh Water / Q000469:parasitology*; D017404:In Situ Hybridization, Fluorescence / Q000379:methods; D008969:Molecular Sequence Data; D010802:Phylogeny; D010839:Phytoplankton / Q000469:parasitology; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid
chemical_list: D048028:DNA, Algal; D004271:DNA, Fungal; D016054:DNA, Protozoan; D004275:DNA, Ribosomal; D012337:RNA, Ribosomal, 18S