Molecular characterization of acquired phototrophs and their plastids in marine communities

Acquired phototrophy is a form of mixotrophy that involves host associations with prey chloroplasts or intact algal cells as symbionts. In marine ecosystems, acquired phototrophy is widespread and alters community interactions by increasing the size class of primary production. The impact of this shift varies from enhancing growth efficiency of host cells (e.g. plastidic oligotrichs) to fueling highly productive bloom events (e.g. Mesodinium rubrum). Here we test the hypothesis that certain acquired phototrophs (e.g. M. rubrum) have species-specific prey and plastid associations, while others (e.g. plastidic oligotrichs) are generalists. Using single cell PCR and taxon-specific primers, we characterized the diversity of acquired phototrophs and their plastids in a variety of coastal marine ecosystems. In certain cases we also compare these data to community plankton diversity, using next-generation sequencing approaches. We demonstrate that Mesodinium blooms may be attributed to several clades from the M. rubrum complex, as well as M. major, and that all of these bloom events are dominated by T. amphioxeia plastids. In contrast, analysis of single M. rubrum cells from non-bloom situations can yield a more complex picture of cryptophyte associations. We also present results on host and plastid diversity of Dinophysis sp., Perispira sp., and Tontonia sp. Our results reveal that while certain species of acquired phototrophs are plastid specialists, cryptic diversity of plastid genes revealed by single cell PCR also implies some level of flexibility in prey uptake.