Nitrogen Cycle: Mechanisms and Microbial Processes

This lecture covers the nitrogen cycle, focusing on nitrogen fixation, nitrification, and denitrification processes. It begins with an overview of nitrogen fixation, detailing the role of nitrogenase and the strategies organisms use to protect this enzyme from oxygen. The instructor explains how certain bacteria, like Azotobacter and cyanobacteria, utilize various mechanisms to facilitate nitrogen fixation in aerobic conditions. The lecture then transitions to nitrification, describing the oxidation of ammonia to nitrite and subsequently to nitrate, highlighting the key enzymes involved, such as ammonia monooxygenase and nitrite oxidoreductase. The discussion includes the importance of these processes in soil and aquatic ecosystems. Finally, the lecture addresses denitrification, explaining how nitrate is reduced to nitrogen gas under anoxic conditions, emphasizing the environmental implications of these microbial processes. The instructor also discusses the production of nitrous oxide as a byproduct and its significance as a greenhouse gas, concluding with the role of anaerobic ammonium oxidation in the nitrogen cycle.