Which type of bacteria is responsible for converting atmospheric nitrogen into ammonia?

The type of bacteria responsible for converting atmospheric nitrogen into ammonia is known as nitrogen-fixing bacteria. These bacteria play a crucial role in the nitrogen cycle, which is essential for life on Earth. They have the unique capability to convert nitrogen gas (N₂) from the atmosphere into ammonia (NH₃) through a process known as nitrogen fixation.

This process is vital because most living organisms cannot utilize atmospheric nitrogen directly, but they can use ammonia as a source of nitrogen for the synthesis of amino acids and nucleic acids. Nitrogen-fixing bacteria can often be found in the root nodules of leguminous plants, forming a symbiotic relationship that benefits both the bacteria and the plants.

In contrast, nitrifying bacteria convert ammonia into nitrites and then nitrates, contributing to soil fertility. Denitrifying bacteria convert nitrates back into nitrogen gas, completing the nitrogen cycle by releasing nitrogen back into the atmosphere. Pathogenic bacteria, on the other hand, are involved in causing diseases and do not play a role in the nitrogen cycle.

Therefore, the answer correctly identifies nitrogen-fixing bacteria as the key organisms involved in the conversion of atmospheric nitrogen into ammonia, emphasizing their importance in ecological processes.