The nitrogen cycle is one of the most important nutrient cycles on the planet. Nitrification, the biological conversion of ammonium to nitrate, occurs in almost all environments, including soils, sediments, fresh and marine waters and wastewater, and can cause serious environmental problems such as promotion of algal blooms and subsequent creation of dead zones in aquatic systems. This research project concerns the first and rate limiting step of nitrification, the oxidation of ammonia to nitrite. Ammonia-oxidizing bacteria have been studied for over 100 years, and until recently scientists assumed that they were the sole microbes responsible for ammonia oxidation in the environment. However, a new player in the oxidation of ammonia to nitrite was discovered very recently, the ammonia-oxidizing Archaea. Both groups use the same resources due to the similarity in their basic energy generating metabolism, and are found in a wide variety of environments together. This project will address the question of which group of ammonia-oxidizing microbes is responsible for ammonia oxidation in different habitats. The project focuses on open water and bottom sediment habitats in Lake Acton, a freshwater lake in Ohio, and will test the hypothesis that these two groups of ammonium oxidizing microbes display niche differentiation. The experimental efforts will focus on cultivation dependent approaches to investigate the response of ammonia-oxidizing microbes to environmental factors under controlled conditions in the laboratory. In addition, a novel culture transplant experiment will be used to link the response of the Archaea and bacteria to natural conditions in the lake.
This project will contribute more broadly to strengthen interdisciplinary research in microbial ecology through the collaboration of two early career scientists. Graduate and undergraduate students will be engaged in active research on the project and participate in a genome annotation project. In addition, a one-week class will be developed and offered at Miami University to educate K-12 teachers about water quality with a focus on wastewater treatment and water purification.
The global nitrogen cycle is one of the most important nutrient cycles in the environment. Nitrification - the biological conversion of ammonium to nitrate - is widely distributed in almost all environments, including soils, sediments, fresh and marine waters and wastewater. The end product - nitrate - can cause serious environmental problems such as promotion of algal blooms and subsequent creation of dead zones in aquatic systems. Ammonia oxidation to nitrite is the first and rate-limiting step of nitrification. Ammonia-oxidizing bacteria (AOB) have been studied for over 100 years, and until relatively recently scientists assumed that they were the sole microbes responsible for aerobic ammonia oxidation in the environment. However, 10 years ago a new player in the oxidation of ammonia to nitrite was discovered, the ammonia-oxidizing Archaea (AOA). Both groups use the same resources due to the similarity in their basic energy-generating metabolism, and are found in a wide variety of environments together. We investigated the distribution of AOA and AOB in different freshwater environments and the response of these microbes to environmental factors important in freshwater environments. The results showed that under laboratory conditions AOA had an advantage under ammonium/nutrient-limited conditions, while AOB grew better when ammonium was present in surplus. Starvation affected the two groups different, AOB recovered faster than AOA. Together these results indicated that the AOB can react faster to changing conditions while AOA are able to grow better under low ammonium supply. In the water column of a variety of lakes (from oligotrophic to eutrophic) AOB were dominant over AOA and growth experiments in lake water showed that AOB grew in water from all lakes while the growth of the AOA was inhibited. Therefore we assume that additional factors besides the nutrient concentration and trophic state control the abundance and community composition of ammonia oxidizers in the water column of freshwater environments. This project connected microbiology with ecology by using general ecological concepts to investigate the interactions of two metabolically similar but phylogenetically distinct organisms – Bacteria and Archaea. Two graduate (1 PhD and 1 master student) and 3 undergraduate students were involved in active research directly connected to the project. Four undergraduate students were participating in genome annotation projects.