Allison Lee, 2018, Ecology and Evolutionary Biology

Allison Lee ’18

Durring my internship, I studied biological nitrogen fixation. Specifically, I focused on how this process affects the nitrogen stable isotope composition (15N/14N) of biomass. Previous research showed that molybdenum, vanadium, and iron-only variants of the iron-rich metalloenzyme nitrogenase, which is responsible for all biological nitrogen fixation, produce biomass with characteristically different 15N content. To explore the mechanisms underlying 15N changes during nitrogen fixation, I grew mutant strains of the model nitrogen fixer, Azotobacter vinelandii, using Mo- or V-nitrogenase under iron replete to limiting conditions. I found that N2 fixation based on Mo-nitrogenase yielded heavier 15N biomass compared to that based on V-nitrogenase, irrespective of the iron treatment. For growth using each metalloenzyme, I uncovered a correlation between iron availability and 15N content. The results of my work suggest that iron availability, in addition to the type of nitrogenase metalloenzyme, controls the 15N content of nitrogen fixer biomass. This work sparked a growing interest in research, and I am looking forward to continuing my work in the Zhang and Morel labs during my time at Princeton.