Significant Effects of Associated Microorganisms on the Community of Photosynthetic Picoeukaryotes.

Photosynthetic picoeukaryotes (PPEs) form associations with other microorganisms. However, whether and how the associated microbes affect PPE communities remain unknown. We used flow cytometric cell sorting combined with parallel high-throughput sequencing of the 18S and 16S rRNA genes to simultaneously investigate PPEs and their associated microbial communities in the Yangtze-connected Lake Dongting. The lake harbors a great diversity of PPEs. PPE communities exhibited significant temporal rather than spatial variations. Two distinct PPE taxa affiliated with Discostella nipponica and Poterioochromonas malhamensis were dominant during winter/spring and summer, respectively. Parallel high-throughput sequencing revealed a great diversity of associated bacteria and non-pigmented eukaryotes (NPEs) in PPEs sorts. Proteobacteria, Actinobacteria, Bacteroidetes, and Cyanobacteria among the associated bacteria and fungi among the associated NPEs were dominant. PPEs were more apparently associated with bacteria than with NPEs. The co-occurrence network of PPEs and associated microbes formed five major modules, which exhibited distinct temporal patterns, being specific to a certain period. Variations in PPEs communities were significantly correlated with both environmental factors and associated microbial communities. In variation partitioning analysis, the associated bacteria explained the greatest variations in PPE communities, and associated bacteria and NPEs co-explained a large portion of environmental effects on PPE communities. Our results highlight the significance of associated microbes in shaping PPE communities.