What role do soil bacteria play in denitrification?

Soil bacteria play a crucial role in the nitrogen cycle, particularly during the denitrification process. Denitrification is the conversion of nitrates (NO3-) back into nitrogen gas (N2), which is then released into the atmosphere. This process is essential for returning nitrogen to the atmosphere and maintaining the balance of nitrogen in the environment.

The correct choice highlights how certain types of bacteria, such as Pseudomonas and Paracoccus, utilize nitrates as an alternative electron acceptor during respiration. In doing so, they effectively reduce nitrates to nitrogen gas, which helps in preventing the accumulation of nitrates in the soil and contributes to the overall cycling of nitrogen in ecosystems.

Other choices, while related to nitrogen, do not pertain to the denitrification process. Certain soil bacteria do indeed fix nitrogen from the atmosphere (which is the job of nitrogen-fixing bacteria) and convert nitrogen gas into ammonia (involves different processes and bacteria). Photosynthesis is a process carried out by plants and some bacteria, but it is unrelated to denitrification and involves capturing sunlight to produce energy rather than processing nitrogen in the soil.