Nitrifying Bacteria

DURING the course of investigations on nitrification in soil and in a sugar beet effluent filter bed, several different bacterial strains have been isolated capable of oxidising various ammonium salts to nitrite, as shown by the Griess-Ilosva method. This is interesting because it has usually been assumed that nitrite formation was brought about by the varieties of bacteria known as Nitrosomonas and Nitrosococcus first isolated by Winogradsky in 1891. There are, however, scattered references in the literature to other organisms capable of producing nitrite from ammonia, but unfortunately the diagnostic characters given are insufficient for sure identification. Among the well-known characteristics of Winogradsky's organisms are the following: inability to grow on nutrient agar or gelatine, inhibiting effect of organic compounds such as sugar, optimum growth at p H. of 7.7–7.9. In contrast to these the organisms isolated in this laboratory grow well and rapidly on both nutrient agar and gelatine (in the case of the soil forms Winogradsky's medium is unsuitable); the presence of 0.1 per cent sucrose in no way inhibits growth, and in the soil forms definitely stimulates nitrite production. Nitrite formation takes place at a wide range of p H values varying from 4.5 to 7.9.