THE MECHANISM OF NITROGEN UTILIZATION BY AZOTOBACTER

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Abstract
The decrease of NH3-N, NO2-N, and NO3-N, added separately or in combination to solution cultures of Azotobacter chroococcum, A. beijerinckii and A. vinelandii, was detd. Ashby''s soln. was employed, without specific additions of Fe or Mo, and no expts. are reported in which fixation of N occurred in such culture solns. containing fixed N. The velocity of consumption of NO2-N was the greatest; that of NO3-N, the least. In culture solns. containing nitrite, NO2-N disappeared very rapidly, and NH3-N accumulated, but this also disappeared rapidly after the complete disappearance of the nitrite. When nitrate was added to culture soln., a trace of nitrite and an accumulation of ammonia were found in the soln. In culture solns. containing ammonium nitrite, the nitrite was for the most part first reduced to ammonia, even in the presence of added NH3-N, and then absorbed by the bacteria. Azotobacter spp. evidently absorb nitrite, and possibly nitrate, mainly after reduction to ammonia. Hydroxylamine is formed during reduction of nitrite to ammonia.

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