Andrew Babbin, Assistant Professor of Earth, Atmospheric & Planetary Sciences
Bioavailable inorganic nitrogen limits the fertility of many environmental systems, from local lakes and rivers to coastal bays to much of the global ocean. Denitrification is a multi-step microbial pathway by which environmental bacteria naturally consume inorganic nitrogen. Denitrification has generally been considered an anaerobic process, requiring the complete absence of molecular oxygen to commence, but mounting evidence has shown that denitrifying bacteria are tolerant of low oxygen concentrations. The exact tolerances of these organisms to denitrify in the presence of oxygen are as yet unknown. Moreover, as denitrification can generate a variable amount of nitrous oxide byproduct under different oxygen conditions, the implications for the production of this greenhouse and ozone-depleting gas remain unexplored. The proposed work aims to resolve how oxygen concentrations shape the activity, community development, and efficiency of denitrifying bacteria. By investigating the response of a laboratory model organism, Pseudomonas aeruginosa, to finely controlled concentrations in oxygen, broad inferences can be made about the tolerance of these facultative anaerobes to aerobic conditions. Furthermore, by using modern genetic engineering techniques, the community responses can be generalized for many systems in terms of how denitrification steps are divided among individual bacteria and the net effect on biogeochemistry.