Which type of bacteria converts nitrates into free atmospheric nitrogen?

Denitrifying bacteria play a crucial role in the nitrogen cycle by converting nitrates (NO3-) into free atmospheric nitrogen (N2). This process, known as denitrification, typically occurs in anaerobic conditions, such as waterlogged soils or deep sediments, where oxygen is limited. During this process, denitrifying bacteria utilize nitrates as an alternative electron acceptor in their metabolic processes, ultimately resulting in the release of nitrogen gas into the atmosphere.

The action of denitrifying bacteria is essential for maintaining the balance of nitrogen in ecosystems, helping to prevent the accumulation of nitrates in the soil or water, which can lead to environmental issues such as eutrophication. Consequently, the correct answer highlights the role of denitrifying bacteria in transforming nitrates into gaseous nitrogen, completing the nitrogen cycle by returning nitrogen back to the atmosphere where it can be utilized by various forms of life.