Comparison of the metabolism of ammonia and molecular nitrogen in Azotobacter.

An earlier report (1) dealing with the distribution of isotopic nitrogen in cells of Axotobacter vinelandii fixing molecular nitrogen provided evidence that ammonia might be the initial stable form of nitrogen in the fixation process. This conclusion was based on the observation that the N’s supplied this organism accumulated in the glutamic acid fraction, as had been already observed in higher plants (2) and animals (3) supplied ammonium labeled with the heavy nitrogen isotope. Comparable studies in which ammonium containing N15 was given to Azotobacter vinelandii are reported here.