Bacteria that convert nitrates into free nitrogen are:

Explanation

Denitrifying bacteria are responsible for converting nitrates (NO3-) into free nitrogen gas (N2) through a process known as denitrification. This process helps to return nitrogen in the environment back to its atmospheric form, completing the nitrogen cycle. Denitrification occurs in anaerobic conditions (environments with little to no oxygen), where these bacteria use nitrates as an alternative source of oxygen, leading to the production of nitrogen gas.