Which type of bacteria is involved in converting nitrates into atmospheric nitrogen?

Denitrifying bacteria play a crucial role in the nitrogen cycle by converting nitrates (NO3-) in the soil into atmospheric nitrogen gas (N2). This process, known as denitrification, occurs under anaerobic conditions where oxygen is scarce. Denitrifying bacteria such as those in the genera Pseudomonas and Paracoccus utilize nitrates as an electron acceptor during their respiration process, thereby releasing nitrogen gas back into the atmosphere. This is vital for maintaining the balance of nitrogen in soil and reducing excess nitrates that can lead to environmental issues like water pollution.

In contrast, nitrifying bacteria are involved in the conversion of ammonia (NH3) to nitrites (NO2-) and then to nitrates (NO3-), playing a different role in the nitrogen cycle. Photosynthetic bacteria primarily engage in the conversion of sunlight into chemical energy, and fermenting bacteria are involved in breaking down organic materials in the absence of oxygen. Therefore, denitrifying bacteria are specifically responsible for the conversion of nitrates back to atmospheric nitrogen, making this the correct choice.