Growth of two serotypes of Nitrobacter in mixotrophic and chemoorganotrophic conditions

The influence of organic compounds (pyruvate, yeast extract, and peptone) was tested on two Nitrobacter serotypes. In mixotrophic conditions, these compounds caused swelling of the cells. As shown by immunofluorescence, multiplication of the nitrifying bacteria still occurred in the absence of nitrite. Although growth was slower under such conditions, the organic substrates were used as energy sources. However, the response of the different serotypes studied varied and this could explain the fluctuations of the two nitrifying populations in the soil.