Question

a bacterium that convert atmospheric nitrogen into label form

Answer 1

Rizobium bacterium here is your answer

Answer 2

The process of converting nitrogen inthe atmosphere to usable forms is a complex process called nitrogenfixation. Certain prokaryotes convert atmospheric nitrogen to ammonia, NH3. The bacteria use some ammonia for their own metabolism, and release the excess.
Nitrogen fixation is the process in which diatomic nitrogen is converted into ammonia by bacteria like Rhizobium, Azotobacter, etc.