Hydroxylamine as an Intermediate in Nitrification

Abstract

AMMONIA is oxidized to nitrite by micro-organisms of the Nitrosomonas group. Many attempts have been made to identify the intermediate compounds in this oxidation; but none has so far been successful. It has been suggested¹ that one intermediate might be hydroxylamine, and there is indirect evidence² that hydroxylamine is formed during nitrification in soil. On the other hand, it is not nitrified in soil³, even in concentrations as low as 7 µgm. N/ml., nor is it nitrified at a concentration of 28 µgm. N/ml. in culture⁴. Experiments carried out on washed suspensions of Nitrosomonas in this laboratory have now shown that while hydroxylamine is toxic to the nitrification of ammonia, and is not itself nitrified at concentrations in excess of a few micrograms nitrogen per millilitre, yet at concentrations below about 1.5 µgm. N/ml. it is nitrified as rapidly as ammonia and is thus a possible intermediate in the nitrification process.