Physiological interrogation of ammonia oxidation by metal limitation, through the lens of stable isotope dynamics

Nitrogen is an important nutrient for all living things on Earth. Across all ecosystems, nitrogen may exist in several different forms, which greatly affects how easily it can be used. Microbial processes are the primary drivers for transforming these different forms. One of these especially widespread processes is called nitrification, which is the oxidation of ammonia into nitrite. The bacteria and archaea that perform this reaction are also known to produce the greenhouse gas, nitrous oxide (or laughing gas), which, because it survives for a very long time in Earth’s atmosphere, is important for being able to predict future changes to Earth’s climate. It is not well-understood how different environmental conditions may affect how well these microbes perform nitrification, and how this influences how much nitrous oxide they produce. This project will work towards understanding how the micronutrients iron and copper impact their activity, with the hope of better understanding what controls this processes in the environment. Results of this project should offer an improved understanding of this critical cycling process with implications for water quality, ecosystem health, wastewater management, agriculture, and climate change. In this project the researchers plan to use stable isotopes of nitrogen and oxygen as tools for investigating how the availability of key metals, iron and copper, may influence the physiology of these ammonia oxidizing organisms. Both ammonia oxidizing bacteria (AOB) and archaea (AOA) require iron and copper for core metabolic machinery, so the researchers hypothesize that limitation of these micronutrients will give rise to changes in their growth and metabolism, and possibly even in their production of nitrous oxide. Production of nitrous oxide by these organisms appears to arise from multiple pathways, the regulation of which remains poorly understood. Through a series of batch and continuous culturing approaches and application of stable isotope tools, the researchers aim to help disentangle underlying controls on nitrous oxide production during nitrification and improve our understanding of this process overall. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.