Evaluation of sequential filtration and centrifugation to capture environmental DNA and survey microbial eukaryotic communities in aquatic environments.

Sequential membrane filtration of water samples is commonly used to monitor the diversity of aquatic microbial eukaryotes. This capture method is efficient to focus on specific taxonomic groups within a size fraction, but it is time-consuming. Centrifugation, often used to collect microorganisms from pure culture, could be seen as an alternative to capture microbial eukaryotic communities from environmental samples. Here, we compared the two capture methods to assess diversity and ecological patterns of eukaryotic communities in the Thau lagoon, France. Water samples were taken twice a month over a full year and sequential filtration targeting the picoplankton (0.2-3 μm) and larger organisms (>3 μm) was used in parallel to centrifugation. The microbial eukaryotic community in the samples was described using an environmental DNA approach targeting the V4 region of the 18S rRNA gene. The most abundant divisions in the filtration fractions and the centrifugation pellet were Dinoflagellata, Metazoa, Ochrophyta, Cryptophyta. Chlorophyta were dominant in the centrifugation pellet and the picoplankton fraction but not in the larger fraction. Diversity indices and structuring patterns of the community in the two size fractions and the centrifugation pellet were comparable. Twenty amplicon sequence variants were significantly differentially abundant between the two size fractions and the centrifugation pellet, and their temporal patterns of abundance in the two fractions combined were similar to those obtained with centrifugation. Overall, centrifugation led to similar ecological conclusions as the two filtrated fractions combined, thus making it an attractive time-efficient alternative to sequential filtration.