Significance of metabolic interactions of diatom-diazotrophic associations (DDAs) for ocean ecosystems

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Diatoms (i.e., Hemiaulus) with symbiotic heterocystous cyanobacteria (i.e., Richelia) are considered responsible for a significant proportion of di-nitrogen (N2) and carbon (C) fixation in the World's oceans. Although these associations often form large and expansive blooms, measures of their N2 and C fixation are few, and current nitrogen (N) and C budget models do not include their contributions to new and primary production. This is largely due to the difficulty in collection and identification of these unique consortia. The investigators will use newly developed genetic and stable isotope techniques and high resolution nanometer-scale secondary ion mass spectrometry (nanoSIMS) approaches to directly resolve the N2 (and C) fixation contributions of these symbiotic diatoms on a relevant spatial scale.The project will enable investigators to explore the metabolic interactions of diatom-diazatoph symbioses and identify environmental conditions that promote the activity of one symbiosis over the other. The three general questions driving the research are: 1) How do the individual diatom-cyanobacteria symbioses differ with respect to their cell specific N2 and C fixation rates; 2) What is the time scale at which N is transferred from symbiont to host; 3) What are the physical and chemical conditions that promote the activity of the different symbioses. The broader impacts of the research involve advancing our knowledge of metabolic interactions between marine microorganisms, and providing a better understanding of marine planktonic symbioses. In addition, the project will contribute to an on-line web library of photographs for educational outreach. Furthermore, it will support training and education to an undergraduate senior thesis project, and will advance our knowledge of the activity of marine microorganisms.