Diversity of photosynthetic picoeukaryotes from eutrophic shallow lakes

METZ, S.; LOPES DOS SANTOS, A.; CASTRO, M.; BIGEARD, E.; ZAGARESE, H.; NOT, F.; LARA, E.; UNREIN, F.

Workshop; 18th Workshop of the International Association of Phytoplankton Taxonomy and Ecology (IAP); 2017

The diversity of photosynthetic picoeukaryotes (PPEs) from marine ecosystems has been intensively studied during last decades, whereas the composition of freshwater PPE remains largely ignored. Here, we combined flow cytometry, microscopy and high throughput sequencing (Illumina Miseq) to study the PPE diversity in six eutrophic and turbid shallow lakes across South America. Molecular diversity data were obtained from total plankton community on filter (FTP) samples (1% in each sample. As expected, most reads from the sorted population belonged to photosynthetic organisms (avg. 82% of the total sequences). Treubouxiophyceae dominated PPE communities in 4 lakes (50 - 90% of the sequences), while Chlorophyceae and diatoms dominated in the two other lakes. Potential parasites (mostly Chytridiomycetes and Ichthyosporea) were relatively abundant (range 10 - 45% of the sequences) in the lake dominated by diatoms. Dominant Treubouxiophyceae OTUs belonged to Choricystis, Chlorella (sensu stricto) and Nannochloris clades; Chlorophyceae to genera Mychonastes and Diatoms to the pico-sized Cyclotella and Chaetoceros genera. Dominant groups among PPEs (e.g. Treubouxiophyceae) were poorly represented in FTP samples. Richness of Treubouxiophyceae was on average 2 orders of magnitude higher in the sorted samples. Moreover, a significant number of OTUs were exclusively found in the sorted, PPE enriched, samples, emphasizing that sequences from FTP sample underestimates the diversity of these small organisms. Besides, 30% of the OTUs had a low similarity (