Carbon and Nitrogen acquisition and cycling in heterotrophic and mixotrophic ciliates

University Of Connecticut, Storrs CT

Investigators

Abstract

Much progress has been made in the last quarter century in understanding the roles of both eukaryotic and prokaryotic microbes in the ecology of the ocean. A good deal of this progress has been made by the application of experimental techniques to natural microbial communities in situ. However, as we learn more about the unique physiological and behavioral features of different individual species, especially of eukaryotic microbes in the ciliate and dinoflagellate clades, there is a need for traditional isolation, cultivation, and experimentation to clarify metabolic potential and ecological roles of different species. Given the widespread occurrence of mixotrophy among microbial eukaryotes, the investigators believe it is important to examine the connections between feeding, photosynthesis, and C and N cycling in particular species that are known to be quantitatively important and widely distributed globally. As a result, the investigators have developed experimental tests of hypotheses related to the use of nitrogen and carbon by planktonic ciliates to evaluate the use of dissolved inorganic (DIN) and organic nitrogen sources in four species (Strombidinopsis sp., Laboea strobila, Strombidium stylifer, and Mesodinium rubrum) whose carbon metabolisms range from strict heterotrophy to near-strict autotrophy. The investigators will also measure assimilation and growth efficiencies of these ciliates (for both C and N) and quantify the role of food and light in nitrogen excretion and internal cycling. For the three mixotrophic forms, the investigators will measure the extent of dissolved inorganic carbon (DIC) cycling between photosynthesis and respiration and evaluate what factors control recycling vs excretion of DIN and DIC. The experimental approach will be to use 15N and 14C isotopes as tracers and to employ a pulse/chase design to measure separately the uptake and excretion of N and C in laboratory isolates. The broader impacts of this proposal include training of graduate students and one post-doc as well as outreach to K-12 educators. In addition, data resulting from this project will be made available through the internet as well as in publications.