Dinitrogen Fixation by Cultures of Frankia sp CpIl Demonstrated by N(2) Incorporation.

The filamentous bacterium Frankia of the Actinomycetales, isolated from the nitrogen-fixing root nodules of certain woody plants, has shown nitrogenase activity in culture, using the acetylene reduction method. In the present work, nitrogenase activity in pure cultures of Frankia sp. CpIl is confirmed using mass spectrometric measurements of (15)N(2) incorporation. After addition of carrier NH(4) (+) to digested cultures, those exposed to (15)N(2) (25 atom%) had a (15)N content of 3.16 atom% compared to 0.354 atom% (15)N in the controls.