Final answer:
Nitrogen fixation through bacteria typically requires an environment with limited or no oxygen because the enzyme nitrogenase is inactivated by oxygen. Bacteria like rhizobia create these conditions in legume root nodules, facilitating nitrogen fixation.
Step-by-step explanation:
Biological nitrogen fixation (BNF) is a crucial process in the nitrogen cycle, performed by certain prokaryotes like soil bacteria, cyanobacteria, and Frankia spp. These organisms help convert atmospheric nitrogen into forms that plants can use, primarily ammonia. Nitrogenase, an enzyme involved in this process, is sensitive to oxygen and is thus inactivated in its presence. Consequently, nitrogen fixation through bacteria generally requires conditions where oxygen is either absent or very limited. For example, symbiotic bacteria such as rhizobia interact with legume plants to form nodules where an oxygen-free environment allows nitrogenase to function and fix nitrogen. Additionally, anaerobic conditions are present in marine and freshwater sediments where other bacterial species can oxidize ammonia in a process called anammox (anaerobic ammonia oxidation).