Marine Microscale Interactions: Exploring the Ecological Relationships Between a Cosmopolitan Eukaryotic Diatom Thalassiosira rotula and its Associated Heterotrophic Bacterial Assemblage

Interspecies microscale interactions between eukaryotic marine diatoms and heterotrophic bacteria play a role in global oceanic biogeochemical cycling by influencing nutrient and carbon cycling, rates of primary production, and phytoplankton community structure. Studies have shown that marine diatoms carry a specific bacterial assemblage in their phycosphere, but little research has been done to identify these bacterial species and to characterize their ecological relationships despite their strong potential to regulate diatom growth and production. In order to further explore ecological interactions between bacteria and diatoms, we are characterizing the taxonomic composition of phycosphere communities from isolates of the cosmopolitan marine diatom Thalassiosira rotula collected from around the globe and identifying whether environmental factors, different host T. rotula strains, space or season correlate with different phycosphere communities. For our initial analyses, we amplified and sequenced the 16S rDNA v34 region of the phycosphere assemblage of 53 T. rotula isolates from eight locations around the globe and obtained > 420,000 paired-end sequences. We identified > 250 different bacterial operational taxonomic units (OTUs). Although many OTUs were shared across populations which identified to members of Alphaproteobacteria and Gammaproteobacteria, we identified distinct bacterial assemblages associated with different locations. The presence of distinct phycosphere bacterial communities may regulate diatom growth which potentially affects rates of primary production, nutrient bioavailablity, and, ultimately, energy transfer to higher trophic levels.